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    STREPTOMYCIN

    1.  EXPLANATION

         Streptomycin is a natural aminoglycoside antibiotic produced by
    the soil Actinomycete  Streptomyces griseus. Streptomycin is used
    in combination with penicillins for the treatment of bacterial
    infections in cattle, sheep and pigs.  It is also used in agriculture
    to control bacterial and fungal diseases of selected fruit,
    vegetables, seed, specialized field crops, ornamental crops, and in
    ornamental ponds and aquaria to control algae.

         Both dihydrostreptomycin and streptomycin were evaluated at the 
    twelfth meeting of the Committee (Annex 1, Reference 17).  An ADI was 
    not established for either compound at that time.

         The two compounds are aminoglycoside antibiotics, and are closely
    related in structure as shown in Figures 1 and 2 below.

    FIGURE 2

         Both dihydrostreptomycin and streptomycin are used for treatment 
    of bacterial infections in food-producing animals.

    2.  BIOLOGICAL DATA

    2.1  Biochemical aspects

    2.1.1  Absorption, distribution and excretion

    2.1.1.1  Mice

         After subcutaneous injection of 5000 to 50 000 units
    streptomycin/kg bw in mice peak blood concentrations of 6.5 units/ml
    were reached in approximately 15 minutes. After oral administration of
    high doses (200 000 units/kg bw) peak blood levels of 2 units/ml were
    reached at 45 to 60 minutes (Stebbins  et al., 1945).

    2.1.1.2  Rats

         See section 2.1.1.1 of the monograph on dihydrostreptomycin for
    the results of studies on streptomycin.

    2.1.1.3  Rabbits

         After administration of a single i.v. dose of 5000 units
    streptomycin/kg bw to rabbits, 5-10% of the dose was recovered in bile
    over 8 hours after injection.  Following intraduodenal administration
    of 8000 units/kg bw, no drug was detected in bile after the same time
    period (Stebbins  et al., 1945).

    2.1.1.4  Dogs

         After oral administration of 420 000 units streptomycin to dogs,
    no drug was detected in plasma, but up to 3.9% of the dose was
    recovered from urine (Graham  et al., 1946).

         After oral administration to dogs of 100 000 to 200 000 units/kg
    bw streptomycin, no drug was detected in bile and 5-10% was recovered
    in urine. In dogs killed 24 hours after drug administration, 60-80% of
    the drug was recovered unabsorbed from the gastrointestinal tract
    (Stebbins  et al., 1945).

         After repeated i.m. administration of 3685-3740 units
    streptomycin/kg bw to dogs every 3 hours, therapeutic blood
    concentrations of 3-18 units/ml were maintained (Stebbins  et al.,
    1945).

         The volume of distribution in dogs after injection of 20 mg/kg bw
    streptomycin was 23% to 36% of body weight, corresponding to
    extracellular fluid volume. Renal clearance appeared to be by
    glomerular filtration alone, and was 34-59 ml plasma/minute (Marshall,
    1948).

    2.1.1.5  Monkeys

         After i.m. administration of 10 000 or 50 000 units
    streptomycin/kg bw to groups of 2 monkeys, 61-69% and 38-42% of the
    dose was excreted in urine, respectively, after 1 day. After repeated
    daily injections for 5 days, the amount recovered in urine per day did
    not differ significantly over the course of treatment (Stebbins
     et al., 1945).

    2.1.1.6  Cattle

         Streptomycin was eliminated in the milk of cattle from 6 to 18
    hours after a single i.m. dose of 5 mg/lb bw (11 mg/kg bw). Absorption
    of streptomycin after intramammary infusion was poor; it was
    undetectable in blood, but significant amounts were detected in urine
    up to 27 hours after intramammary infusion (Huber, 1966).

    2.1.1.7  Humans

         Aminoglycoside antibiotics cross membranes very poorly and Pratt
    & Fekaty (1986) have reported that only about 1% of an oral dose is
    absorbed, even when there is intestinal inflammation or ulceration. 

         Anderson and Jewell (1945) reported that after oral
    administration of 600 000 units of streptomycin to a fasted patient,
    no drug was detected in serum for the following 12 hours when assayed
    micro-biologically using  Staph. aureus. Failure to detect serum
    levels of the drug could not be attributed to inactivation of the drug
    by gastric juices, since incubation in gastric juice  in vitro at 37
    C for 3 hours did not produce any loss of activity.

         Elias and Durso (1945) also reported no demonstrable streptomycin
    in blood after oral administration of 4 000 000 units streptomycin.
    Only 1% of the dose was recovered in urine and >64% was eliminated in
    faeces.

         Dollery (1991) reported that after oral administration of
    streptomycin, 60%-100% of the drug was recovered unchanged from the
    faeces. 

         Streptomycin is poorly absorbed by inhalation, therefore high
    levels may be produced in respiratory secretions, causing a marked
    decrease in bacterial flora in the upper respiratory tract (Huber,
    1966).

         Pharmacokinetic parameters in humans following i.m.
    administration are summarized in Table 1.

         The volume of distribution of streptomycin ranged from 30-35%
    body weight, corresponding to the extracellular fluid volume.
    (Marshall, 1948).

         Approximately 0.5% of the maternal dose of streptomycin was
    excreted in breast milk in 24 hours; thus, a nursing infant could
    ingest approximately 5 mg in 24 hours.  The recommended therapeutic
    dose for infants is 10-20 mg/kg bw/day (Dollery, 1991).

         After parenteral administration of streptomycin, approximately
    50% to 60% of the dose was excreted unchanged in the urine within 24
    hours (Anderson & Jewell, 1945).

    Table 1.  Pharmacokinetic parameters for streptomycin in humans

                                                                        

    Adult daily therapeutic dose            15-25 mg/kg bw/day
    Route of administration                 Intramuscular
    Normal dosage interval                  12 hours
    Peak serum level                        25-30 ug/ml

    Half-Life:
    Normal                                  2.5 hours
    Anuric                                  50-110 hours
    elderly*                                9 hours
    premature/newborn infants*              7 hours

    Volume of distribution
    well-nourished patients*                95.9  19.5 litres
    malnourished patients*                  66.3  7.4  litres

    Plasma protein binding                  35%
                                                                        

    (Pratt & Fekaty, 1986  / * = Dollery, 1991)

         Renal clearance values for streptomycin ranged from 30-80 ml
    plasma/minute in humans after i.v. infusion of 10-20 mg/kg bw in 100
    ml saline over 10 minutes (Marshall 1948).  A small amount of
    reabsorption occurs at the proximal tubules (Pratt & Fekaty, 1986).

         Approximately 20% of a parenteral dose of streptomycin could not
    be accounted for in urine, but no metabolites have yet been
    identified. Approximately 1% was excreted in bile (Dollery, 1991).

         The excretion rate for aminoglycosides after parenteral
    administration is dependent on renal function and is linearly related

    to the creatinine clearance rate. The elimination half-life in adults
    is 2 hours, but 5-6 hours in neonates due to their lower glomerular
    filtration rate (Pratt & Fekaty, 1986).

    2.1.2  Biotransformation

         The aminoglycosides are reported not to be metabolized in humans
    and are excreted in their active forms by glomerular filtration (Pratt
    & Fekaty, 1986).

    2.1.3  Effects on enzymes and other biochemical parameters

         No information available

    2.2  Toxicological studies

    2.2.1  Acute toxicity studies

    2.2.1.1  Mice

         The acute toxicity of various batches of streptomycin of
    different purities, was studied in groups of 5 or 10 mice per dose, by
    various routes of administration.  The oral  LD50 ranged from 15
    000-30 000 mg/kg bw, the s.c. LD50 was 500-550 mg/kg bw, the i.v.
    LD50 was 85-111 mg/kg bw, and the i.p. LD50 was 610-575 mg/kg bw (see
    Table 2). Clinical signs of toxicity prior to death included
    restlessness, respiratory depression, loss of balance,
    unconsciousness, motor paralysis and coma following all routes of
    administration. Coma was more often associated with s.c. dosing. After
    oral dosing, restlessness and excessive thirst were observed, possibly
    due to an osmotic effect. At autopsy, the only gross anatomical or
    histological lesions observed were haemorrhagic lesions in the
    gastrointestinal tract of animals dosed orally. Oral administration of
    sodium chloride of the same tonicity as the streptomycin produced
    similar lesions (Bacharach  et al., 1959).

         In another study, the oral LD50 of various streptomycin salts was
    compared in male Carworth CF1 mice. Streptomycin calcium chloride
    complex gave an LD50 of 8750 mg/kg bw, whereas streptomycin sulfate
    gave an LD50 of 25 000 mg/kg bw (Edison  et al., 1951).

        Table 2.  Acute toxicity of streptomycin in mice
                                                                                  

    Route of administration    LD50 (mg/kg bw)               Reference

                                                                                  
    Intravenous                       85 - 111        Bacharach  et al., 1959

    Intraperitoneal                  610 - 575        Bacharach  et al., 1959

    Subcutaneous                     500 - 550        Bacharach  et al., 1959
                                           600        Molitor  et al., 1946

    Oral

       Base                    15 500 - 30 000        Bacharach  et al., 1959

       Calcium chloride                   8750        Edison  et al., 1951

       Sulfate                          25 000        Edison  et al., 1951

                                                                                  
    
    2.2.1.2  Rats

         Rats were anaesthesized with 30 mg/kg bw nembutal and given
    intravenous infusions of streptomycin at rates of 40, 180, or 600 mg/
    kg/bw/hour. At the high and intermediate infusion rates respiration
    ceased within 6 and 20 minutes, respectively. The heart continued
    beating for 4 to 6 minutes after cessation of respiration. The
    low-dose rats showed no adverse effects when infusion was stopped
    after 1.5 hours, when approximately 60 mg streptomycin had been
    infused. However, doses of 40 to 50 mg had proved fatal when injected
    more rapidly (Molitor  et al., 1946).

    2.2.1.3  Hamsters

         The oral LD50 of streptomycin sulfate in groups of 10 golden
    hamsters was 400 mg/kg bw. The LD50 after s.c. administration was
    >500 mg/kg bw. Some animals died up to 2 weeks after dosing. Clinical
    signs of toxicity included listlessness, ruffled fur, decreased food
    intake, and diarrhoea (DeSalva  et al., 1967).

    2.2.1.4  Guinea-pigs

         The s.c. LD50 for streptomycin was 400 mg/kg bw. The same batch
    of streptomycin produced an s.c. LD50 of 600 mg/kg bw in mice (Molitor
     et al., 1946).

    2.2.1.5  Frogs

         Groups of 5 frogs  (Rana pipiens) were injected with 25 to 
    100 mg of streptomycin in the abdominal lymph sac. Within 15 to 20
    minutes complete motor paralysis had occurred and no respiratory
    movements were observable. The authors reported that, unlike
    warm-blooded animals which would have died of respiratory failure at
    this stage, the frogs completely recovered within 2 to 3 days when
    kept partially submerged in water (Molitor  et al., 1946).

    2.2.1.6  Cats

         Intravenous administration of 10 mg/kg bw "pure" streptomycin to
    cats had no effect on blood pressure; 20 mg/kg bw gradually depressed
    blood pressure, which subsequently returned to normal; very high
    doses, 120 to 375 mg/kg bw, caused vasomotor and respiratory paralysis
    for several hours if artificial respiration was maintained. During
    this period the heart continued to beat regularly. Injection of less
    pure streptomycin concentrates caused a pronounced drop in blood
    pressure with peripheral vasodilation, which the authors concluded was
    due to the presence of a histamine-like impurity (Molitor  et al.,
    1946). 

         The clinical signs of acute toxicity were similar in all species
    after i.v. or s.c. injection of streptomycin (see above), but cats and
    dogs additionally showed signs of nausea, vomiting and ataxia (Huber,
    1966).

         Four out of 12 cats receiving a parenteral dose of 250-350 mg/kg
    bw streptomycin developed respiratory failure.  One animal was
    resuscitated and 3 died (Clark, 1977).

    2.2.1.7  Dogs

         Intravenous injection of streptomycin at doses of 100 to 200
    mg/lb bw (220-440 mg/kg bw) in dogs caused an irreversible depression
    of blood pressure. Respiration was stimulated by low but paralyzed by
    high (165 mg/kg bw) intravenous doses (Huber, 1966).

    2.2.1.8  Monkeys

         Intravenous and s.c. administration of 30 to 70 mg/kg bw
    streptomycin to monkeys caused marked respiratory depression which
    sometimes necessitated artificial respiration (Molitor  et al.,
    1946). 

         Two monkeys each weighing approximately 4 kg, were lightly
    anaesthesized with nembutal. Streptomycin was administered by i.v.
    infusion. The first monkey suffered respiratory depression and died
    after a total dose of 440 mg.  The second monkey tolerated a total

    dose of 1920 mg over 42 hours without any significant change in heart
    rate, respiratory rate or body temperature (Molitor  et al., 1946). 

    2.2.2  Short-term toxicity studies

    2.2.2.1  Mice

         Forty mice were injected s.c. with streptomycin at 150 mg/kg
    bw/day in three equally divided doses for 6 days. Another group of 20
    mice received 1000 mg/kg bw/day in five divided doses subcutaneously
    for 6 days. In a third experiment, groups of mice received 150, 300,
    600 or 1500 mg/kg bw/day orally in the diet. All the mice remained
    clinically normal during treatment and for the following 10-day
    observation period. No gross pathological findings were observed in
    any of the three experiments (Molitor  et al., 1946).

    2.2.2.2  Rats

         Two groups of 60 weanling rats received streptomycin in the diet
    at 300 or 900 mg/kg bw/day. Both groups experienced slightly reduced
    body-weight gain compared to controls. In the 900 mg/kg bw/day group
    nervous hyperexcitability was observed within 24 hours of treatment. 
    In the 300 mg/kg bw/day group this developed after about 6 weeks.
    Animals were otherwise normal and no abnormalities were found at
    necropsy. The duration of the treatment period was not stated in this
    study (Molitor  et al., 1946). 

         A group of 30 rats with an average weight of 215 g were injected
    s.c. with 100 mg/kg bw/day streptomycin in 3 divided doses for 72
    days. No clinical signs of toxicity were observed and no
    treatment-related effects were noted on gross anatomical or
    histological examination (Molitor  et al., 1946). 

         Two groups of 20 rats received 400 mg streptomycin/kg bw/day for
    8 days by s.c. and i.v. injections, respectively. No adverse effects
    were observed in either group (Molitor  et al., 1946).

    2.2.2.3  Hamsters

         Forty hamsters (20 of each sex) were divided into 3 groups and
    fed 2, 10, or 40 mg/kg bw/day streptomycin in the diet. After 6 days,
    all animals in the high-dose group and 90% in the mid-dose group were
    dead.  All animals in the low-dose group survived.

         An escalating dose study was then conducted in which animals were
    initally fed 2 mg/kg bw/day streptomycin in the diet. The dose was
    then doubled every 2 weeks until the dose reached 64 mg/kg bw/day at
    3 months. The streptomycin concentration in the diet was adjusted
    weekly to compensate for body-weight gain. All the animals survived

    the study. Histological examination revealed damage of the intestine,
    caecum and liver in some but not all survivors (DeSalva  et al.,
    (1969).

    2.2.2.4  Guinea-pigs

         Groups of 15 guinea-pigs weighing on average 375 g were treated
    with 20, 30, 40, or 60 mg/kg bw/day streptomycin s.c. in 3 divided
    doses for 6 to 8 weeks. Five animals served as controls. Two animals
    in the 40 mg/kg bw/day group died of unknown causes on day 15 of
    treatment. All other animals remained clinically normal and no
    abnormal findings were noted on gross post-mortem examination (Molitor
     et al., 1946).

    2.2.2.5  Cats

         A daily dose of streptomycin of 25-75 mg/lb bw/day (55-165 mg/kg
    bw/day) to cats (route not stated) caused progressive changes in
    posture and gait over about 20 days, including ataxia (of the hind
    legs first then fore-legs), and a progressive rotational nystagmus.
    Withdrawal of the drug resulted in a slow but complete recovery of
    vestibular function (Huber, 1966).

         Eight cats were administered streptomycin calcium chloride
    complex.  Four cats received  1 g base/kg bw/day orally, two received
    2 g base/kg bw/day orally, and two received 0.1 g base/kg bw/day, s.c.
    The oral doses produced vomiting within 30-45 minutes after dosing.
    Two cats receiving 1 g base/kg bw/day developed ataxia on days 9 and
    12 of dosing; the other 2 cats receiving this dose died on days 8 and
    11 with no signs of neurotoxicity. The 2 cats receiving 2 g base/kg
    bw/day had more persistent vomiting and developed ataxia later (days
    12 and 19). The cats treated s.c. developed ataxia on days 11 and 14
    (Edison  et al., 1951).

         Vestibular function was assessed in 10 cats (5/sex) treated daily
    with oral doses of 40 mg dihydrostreptomycin/kg bw/day for 90 days.
    Streptomycin sulfate was used in this study as a positive control (200
    mg/kg bw/day, s.c.), and water as negative (vehicle) control, by
    gavage. 

         Three cats died, one from each of the negative control, positive
    control, and dihydrostreptomycin groups, due to urinary obstruction,
    which was considered unrelated to treatment.  The results with
    dihydrostroptomycin are described in section 2.2.2.2 of the monograph
    on dihydrostreptomycin.  

         All the streptomycin-treated cats showed clinical signs of
    toxicity after 2 weeks of treatment (disturbed vestibular function
    manifested by ataxia, loss of righting reflex and head oscillations,

    salivation, decreased food and water intake, and decreased body
    weight); therefore, the streptomycin dose was then decreased to the
    maximum tolerated dose based on food and water intake (between 25 and
    100 mg/kg bw/day).  The vestibular dysfunction persisted throughout
    the study even at this lower dose. There were no treatment-related
    effects on ophthalmoscopic examination. Lesions of the respiratory
    system noted during necropsy were considered by the authors as
    secondary to inhalation of fluid from excessive salivation in these
    animals, and not directly resulting from treatment (Tisdel  et al.,
    1976).

    2.2.2.6  Dogs

         Five dogs were injected s.c. or i.m. with streptomycin at 50 or
    100 mg/kg bw/day in three divided doses for 20 days. All animals
    developed proteinuria at 1 to 2 weeks.  Two animals also had decreased
    serum protein. Casts, epithelial cells and leucocytes were observed in
    urine. At necropsy, 1 dog in the high-dose group had liver changes
    suggestive of necrosis, and pale streaks were observed in the kidney
    cortex. Considerable fatty deposits were observed on staining with
    Sudan IV in the central portion of the nephron, and a small amount in
    the liver. Slight tubular necrosis was observed in another dog with
    severe proteinuria. Three dogs developed a change in gait and posture
    suggesting a labyrinthine or cerebellar disturbance. Auditory
    impairment was noted based on failure of these dogs to respond
    normally to sudden noises (Molitor  et al., 1946).

         Dogs treated for cystitis with a daily i.m. injection of 20 mg/lb
    bw/day (44 mg/kg bw/day) streptomycin for 14 days developed vestibular
    dysfunction. Dogs treated with 85 mg/lb bw/day (187 mg/kg bw/day) for
    28 days developed bilateral liquefaction necrosis of the ventral
    cochlear nuclei and a clumping of Nissl-like particles in most of the
    neurons of these nuclei (Huber, 1966).

    2.2.2.7  Monkeys

         A group of 4 monkeys were given daily s.c. injections of
    streptomycin at 25 mg/kg bw/day for 66 days. The material used was
    from 7 different lots, containing between 50 and 170 g streptomycin
    base per mg. All monkeys remained clinically normal, apart from a
    slight anaemia and skin irritation at the injection site. No effects
    were observed on the kidneys as assessed by blood urea, chemical and
    microscopic examination of urine, and histological examination of the
    kidneys (Molitor  et al., 1946).

         A total of 15 monkeys were given 25, 50, or 200 mg/kg bw/day
    streptomycin i.v. for 5 days. The two lower doses were given as 3
    separate injections, and the 200 mg/kg bw/day dose was given as 6
    separate injections daily, in order to minimize respiratory
    depression. Two batches of material were used, pure streptomycin (800 

    g streptomycin base per mg) and streptomycin concentrate (400 g
    streptomycin base per mg). The only adverse effect observed in the 2
    lower dose groups during treatment or the following 10-day observation
    period was an occasional transient impairment of hepatic function as
    judged by the bromosulfophthalein retention test. In the 200 mg/kg
    bw/day group, 1 monkey died on the second day from respiratory
    paralysis following injection. The others survived the 15-day period
    but had transient proteinuria (Molitor  et al., 1946).

         Sixteen monkeys were administered streptomycin by the s.c. or
    i.m. routes at doses of 10, 50, 100 or 200 mg/kg bw/day for 5 days
    followed by a 10-day observation period.  In those receiving 10 or 50
    mg/kg bw/day only injection site reactions were observed. In the 2
    higher dose groups during the 10-day observation period, 3/12 animals
    had transient proteinuria and 2/12 animals had bromosulfophthalein
    retention (Molitor  et al., 1946). 

         All monkeys from the above studies were necropsied 12-20 days
    after the last dose. Injection site damage was observed, especially in
    the monkeys dosed i.m.  Fatty metamorphosis was observed in the liver
    and less often in the kidney in monkeys dosed at 25 mg/kg bw/day or
    greater. There was no decrease in liver glycogen. (Molitor  et al.,
    1946).

         The reversibility of the fatty change observed in the liver and
    kidneys in the above studies was examined in 8 monkeys administered 25
    mg streptomycin/kg bw/day, i.v. for 5 days. Pairs of animals were
    sacrificed on the day after the treatment period, and 10 days, 1 month
    and 2 months later. All animals remained clinically normal. At
    necropsy on the day after the last injection, a moderate amount of fat
    was observed in the liver and none was found in the kidney.  At 10
    days, a large amount of fat was present in liver and a slight amount
    in kidney. At 30 days, there was no fat in the kidney and a slight
    amount in liver. At 66 days no pathological changes were observed
    (Molitor  et al., 1946).

    2.2.3  Long-term toxicity/carcinogenicity studies

         No information available

    2.2.4  Reproductive toxicity studies

         No information available

    2.2.5  Special studies on embryotoxicity/teratogenicity

    2.2.5.1  Mice

         Groups of 6-7 pregnant Swiss mice were given single s.c.
    injections of streptomycin at doses of 0.025 or 0.25 g/kg bw on day
    14 of gestation. There was no effect on litter size and no

    malformations were observed in any of the fetuses. In the low-dose
    group, F1 females had reduced body-weight gain compared to controls
    up to day 24, followed by accelerated body-weight gain, such that at
    35 days, weight was comparable to controls. The same effect was seen
    in males but to a lesser degree. In the high-dose group, the females
    had reduced body-weight gain up to 35 days. Again the same effect was
    observed in males, but only up to day 17. Organ weights were reduced
    for seminal vesicles and adrenal glands (in both sexes) at the low
    dose. At the high dose, all organ weights were reduced except the
    liver. Kidney weight (in both sexes) and adrenal and spleen weight in
    females were most notably reduced (Boucher & Delost, 1964).

         Pregnant C57BL mice were given twice-daily i.m. injections of
    streptomycin at 250 mg/kg bw/injection. The timing of treatment in
    relation to gestation was not stated. There was no effect on litter
    size, no external malformations, and no gross malformations of the
    brain or cranial segments of the cervical medulla. Microscopic
    findings were observed in head sections of 9/52 embryos, which
    included pycnosis, perivascular cell infiltrations, haemorrhages,
    ependymal polypus, and eye anomalies. However, these findings occurred
    with similar frequency in controls and therefore could not be
    attributed to treatment. Streptomycin crossed the placental barrier,
    and was identified by microbiological evaluation of tissue fluids of
    embryos from treated dams (Ericson-Strandvik & Gyllensten, 1963). 

         Streptomycin was administered subcutaneously to 14 pregnant mice
    at 400 g/kg bw/day on days 9, 10, and 11 of pregnancy. Twenty-eight
    mice used as controls were injected with water. The number of implants
    was reduced in treated mice (179 vs 351 in controls). Early deaths
    were higher in controls (3.9% in the streptomycin group vs 5.1% in
    controls). The percentage of fetal deaths and live fetuses were
    similar in treated and control animals. Body weights of treated males
    and females were significantly reduced compared to the controls (p
    <0.001). No malformations were observed in fetuses in the treatment
    group (Nomura  et al., 1984).

         ICR mice were treated i.p. during days 12 to 16 of gestation with
    streptomycin at 250 mg/kg bw/day. Twenty treated and twenty control
    F1 offspring were examined by behavioural tests. The morphology of
    the inner ear was examined by scanning electron microscopy.
    Body-weight increase, activity, and functional development such as
    grooming were unaffected by treatment. Vestibular function (assessed
    with narrow path and rotor rod tests) was reduced compared to
    controls. Morphological changes included degeneration and polyp-like
    cytoplasmic extrusions of the inner hair cells (Nakamoto  et al.,
    1985).

    2.2.5.2  Guinea-pigs

         See section 2.2.5.1 of the monograph on dihydrostreptomycin for
    the results of studies on streptomycin.

    2.2.5.3  Humans

         The incidence of congenital malformations in newborns was
    examined in 1619 mothers who had received treatment for tuberculosis
    with streptomycin, hydrasid and p-amino salicylic acid.  These results
    were compared to a control group of (2711) healthy pregnant women. The
    incidence of congenital malformations was 2.34% in tuberculosis
    infected subjects and 2.56 in controls. No difference was observed in
    the pattern of malformations in the 2 groups; however, the nature of
    these malformations was not specified. The dose and time of treatment
    were not stated. (Marynowski & Sianozecka, 1972).

         See section 2.2.5.3 of the monograph on dihydrostreptomycin for
    the results of other studies on streptomycin.

    2.2.6  Special studies on genotoxicity

         Streptomycin and dihydrostreptomycin bind to and alter the
    configuration of the 30S sub-unit of ribosomes, thus inhibiting
    protein synthesis and causing misreading of the genetic code. RNA and
    DNA synthesis are unaffected (Goldberg, 1965; Davies  et al., 1964).

         The results of genotoxicity assays with streptomycin are
    summarized in Table 3.

    2.2.7  Special studies on ototoxicity

    2.2.7.1  General

         A review of the literature presented by Berg (1951) on
    ototoxicity produced by streptomycin states that histological
    examination of the auditory system of numerous affected species by
    several authors gave either negative findings, or indications that the
    lesion was localized to the central nervous system, or indications
    that the peripheral sensory epithelium of the labyrinths was affected.
    Consequently, it is difficult to draw definitive conclusions on the
    site of streptomycin-induced lesions. Berg postulates that the primary
    lesion is in fact the vestibular sensory epithelium, rather than the
    Organ of Corti, and that changes in vestibular nerves and central
    vestibular nuclei are secondary to this effect, resulting from an
    ascending atrophy (Berg, 1951).


        Table 3.  Results of genotoxicity assays on streptomycin

                                                                                                      
    Test System      Test Object            Concentration      Results          Reference
                                                                                                      

     In vitro

    Cytogenetics     Human lymphocytes      4.7-13.7 mg/ml     Equivocal1       Obe, 1970

    Cytogenetics     Human lymphocytes      50-2000 ug/ml      Negative         Neu 1965

    Cytogenetics     Human lymphocytes      50-300 ug/ml       Inconclusive2    Das & Sharma, 1983

    Cytogenetics     Mammalian cells        10-20 mM           Positive         Kodama  et al., 1980

     In vivo

    Cytogenetics     Human lymphocytes3     0.75-1.0 g/day     Negative         Jaju  et al., 1983

    Cytogenetics     Human lymphocytes4     Therapeutic        Negative         Beek, 1976
                                            does (not stated)

                                                                                                      

    1    Achromatic lesions were induced. The significance of these with respect to mutagenic/carcinogenic
         potential was not established.
    2    Streptomycin was tested in combination with penicillin in this study.
    3    Human lymphocytes were isolated from tuberculosis patients on one of three different treatment
         regimes for a minimum of 3 months: streptomycin and isoniazid; streptomycin, isoniazid and p-amino
         salicylic acid; or streptomycin, isonazid and thiacetazone.  These were compared to lymphocytes
         from healthy humans and newly diagnosed tuberculosis patients prior to initiation of therapy.
    4    Human lymphocytes were obtained from 21 tuberculosis patients on one of the following 6-month
         treatment regimes: streptomycin and p-amino salicylic acid for 3 months followed by 3 months treatment
         with streptomycin, isoniazid and ethambutal; or streptomycin, isoniazid, and rifampicin. These were
         compared to lymphocytes taken from these same patients prior to initiation of treatment.
    

         Streptomycin damages the hair cells of the Organ of Corti in the
    cochlea and the hair cells of the vestibular apparatus which are found
    in the macula of the saccule, the macula of the utricule, and the
    ampullae of the three semicircular canals. It does not damage the
    eighth cranial nerve (Davies, 1991).

    2.2.7.2  Guinea-pigs

         Groups of 3 to 9 guinea-pigs were treated with streptomycin at
    doses of 100-400 mg/kg bw/day for 3 to 6 weeks (the route of
    administration was not specified). On histological examination of the
    inner ear, degeneration of the nerve cells of the central nuclei
    (primarily vestibular and cochlear nuclei), was observed in
    association with clinical signs of hearing loss and vestibular
    dysfunction in each treatment group. Myelin staining of the eighth
    cranial nerve was normal in all animals, as were the sensory cells of
    the labyrinth (Christensen  et al., 1951).

         Tsang and Chin (1963) reported changes in both the peripheral and
    central sides of the vestibular and cochlear systems occurring at the
    same time in guinea-pigs treated for 21-60 days with 200-400 mg/kg
    bw/day streptomycin parenterally. The authors noted that the
    vestibular system was more severely affected than the cochlear system.

    2.2.7.3  Cats

         See section 2.2.8.1 of the monograph on dihydrostreptomycin for
    the results of studies on streptomycin.

    2.2.7.4  Dogs/humans

         Stevenson  et al. (1947) performed neuropathological
    examinations on 5 patients who had died of tuberculosis, and who
    became partially or completely deaf while receiving large doses of
    streptomycin. The doses used were typically 3 g/day i.m. in adults.
    Doses administered to children were proportionally less. In 4/5
    patients, additional doses of streptomycin were administered by the
    intrathecal route (dose not stated).

         A similar examination was made in 3 dogs treated i.m. with 170
    mg/kg bw/day streptomycin for 9 to 28 days.  Clinical signs of
    toxicity included ataxia, head movements, tail-chasing, and weakness.
    One dog died on the 9th day with advanced bilateral necrotising renal
    arteriolitis and glomerulitis. The other two dogs were killed at 28
    days (Stevenson  et al., 1947).

         The findings were similar in dogs and humans.  Degeneration of
    the nuclei of the VIIIth cranial nerve was observed, particularly the
    ventral cochlear nuclei and possibly the inferior vestibular nuclei. 

    The VIIIth cranial nerve was found to be normal in two cases, although
    it was unclear whether this was in humans or dogs (Stevenson
     et al., 1947). 

    2.2.8  Special studies on renal toxicity

         Renal function was assessed in mice, rats, guinea-pigs, and dogs,
    by either a 5-hour observation of water diuresis after a single dose
    of streptomycin or observation of the overnight urine volume (18
    hours) during and after a prolonged course of streptomycin treatment
    in the following experiments:

    1.   Mice were administered either 400 or 800 mg/kg bw streptomycin
         s.c. in 8 divided doses over 24 hours or 150 or 300 mg/kg bw/day
         in 3 divided doses over seven days.

    2.   Groups of rats were administered streptomycin s.c. as a single 
         injection of 100 or 200 mg/kg bw, 100 mg/kg bw/day in divided
         subcutaneous doses for 5 days, or 100 mg/kg bw/day for 8 weeks. 

    3.   Guinea-pigs were administered 30 mg streptomycin/kg bw s.c. in 3
         divided doses over 24 hours.

         No adverse effects were observed on renal function in the above
    experiments (Molitor  et al., 1946).

         In rats treated with 250 or 500 mg/kg bw of "pure" streptomycin
    orally together with a water load, urine output was reduced at 2 hours
    but total output at 5 hours was similar to controls. The rate of
    output was decreased with treatment. With streptomycin concentrate,
    diuresis was decreased even further and the 5-hour urine output was
    less than half of controls. This effect on diuresis had disappeared by
    the third day after treatment (Molitor  et al., 1946).  

         Monkeys were treated with streptomycin at 25, 50, 100 or 200
    mg/kg bw/day s.c. in 3 divided doses for 5 days, 100 or 200 mg/kg
    bw/day s.c. for 10 days, or 25, 50 or 200 mg/kg bw/day i.v. in 3 or 6
    divided doses for 5 days. At the higher doses, proteinuria was
    observed and blood urea increased in most animals but remained within
    the normal range of values for this parameter. Overnight urine volumes
    were occasionally decreased. After intravenous administration of 25
    mg/kg bw/day, overnight urine volumes were reduced on the first day of
    dosing by 18, 67, 75 and 80% in 4 monkeys, but had returned to normal
    by the tenth day of the observation period. Two monkeys dosed with a
    low-potency material had a decreased serum protein level, inflammation
    at the injection site and edema of the abdominal skin and genital
    region extending to the upper leg. This reaction was attributed by the
    authors to a histamine-like impurity present in low-purity batches of
    streptomycin (Molitor  et al., 1946).

    2.2.9  Special studies on local toxicity

    2.2.9.1  Eye

         An aqueous solution of streptomycin (8 mg base/ml) and an
    ophthalmic ointment containing 1 mg/g streptomycin were applied to the
    conjunctival sac of lightly anaesthesized rabbits for 30 minutes.
    Occasional redness of the conjunctiva was observed which persisted up
    to 12 hours after application (Molitor  et al., 1946).

    2.2.9.2  Intrabuccal

         Application of streptomycin as either an aqueous solution (8
    mg/ml) or as an ointment (1 mg/g) to the buccal membrane of dogs for
    15 minutes had no adverse effects (Molitor  et al., 1946).

    2.2.9.3  Intradermal

         Intradermal injection of 0.1 to 0.4 mg streptomycin in the
    abdominal skin of guinea-pigs produced slight reddening followed
    occasionally by blister formation (Molitor  et al., 1946). 

    2.2.9.4  Intrapleural

         Groups of two rabbits were given an intrapleural injection of
    streptomycin at 1, 10, or 100 mg/kg bw. All animals were necropsied on
    the fourth day after injection. Dose-related increases in pleural
    fluid and congestion of the diaphragm were observed; at the high dose,
    small areas of haemorrhage and fibrous adhesions were observed between
    the lung, diaphragm and pleural wall (Molitor  et al., 1946). 

    2.3  Observations In humans

    2.3.1  Ototoxicity

         Patients presenting with ototoxic side effects after treatment
    with streptomycin, dihydrostreptomycin or kanamycin, for various
    clinical conditions, were studied in a retrospective study. The route
    of administration was not stated, although it was probably
    intramuscular injection. 

         Vertigo was reported by the end of the first week of treatment in
    25/26 patients treated with streptomycin alone at doses between 0.25
    and 2 g/person/day (equivalent to 3 to 36 mg/kg bw/day). Total doses
    of 4 g to 71 g were administered. In approximately 70% of cases the
    duration of treatment was short (5 to 14 days) and the total dose was
    low (4 to 10 g). In most cases (13/19 patients) treatment lasted from
    one week to four months. In 6/19 cases the symptoms were still present
    at the last examination performed at 1.5 to 6 years after their first
    appearance. In 13/18 patients functional impairment of renal clearance
    was reported.  These tended to be patients treated for longer periods

    (9 to 19 days). At lower streptomycin doses (15 mg/kg bw/day) for
    about 7 days, only one case of vestibular damage was reported when
    over 1000 patients were treated (Erlanson & Lundgren, 1964).

         See section 2.3.1 of the monograph on dihydrostreptomycin for the
    results of other studies on the aminoglycosides.

    2.3.2  Renal toxicity

         Evidence of minor renal tubular dysfunction, such as urinary
    casts and a minor degree of albuminuria, are not uncommon in humans
    treated with streptomycin. However, severe renal damaage (proximal
    tubular necrosus) is rare (Dollery, 1991).

         Renal damage is usually reversible on cessation of therapy.
    Streptomycin is the least nephrotoxic of the aminoglycosides (Pratt &
    Fekaty, 1986).

         See section 2.3.2 of the monograph on dihydrostreptomycin for the
    results of other studies on the aminoglycosides.

    2.3.3  Neuromuscular blockade

         See section 2.3.3 of the monograph on dihydrostreptomycin for the
    results of other studies on the aminoglycosides.

    2.3.4  Allergic reactions

         Cutaneous and generalized hypersensitivity reactions are common
    with streptomycin and can be severe, the most common features being
    rash and fever (Dollery, 1991).

         Hypersensitivity reactions may occur in response to streptomycin
    treatment. Skin reactions are reported to occur in 5% of patients.
    Severe exfoliative dermatitis and anaphylaxis have occurred.
    Sensitization is common among those handling streptomycin
    occupationally (Martindale, 1993; British Pharmaceutical Codex, 1968).

         Streptomycin has been reported to cause asthma, but such
    reactions are rare compared to those due to penicillin (Davies, 1991).

    2.3.5  Other Effects

         Other toxicities occur rarely and include neutropenia,
    agranulocytosis, and aplastic anaemia. Transient elevation of hepatic
    enzymes occur occasionally (Pratt & Fekaty, 1986).

         Streptomycin has been reported to cause a toxic neuritis of the
    branches of the trigeminal nerve resulting in numbness, tingling or
    burning sensations in the face or mouth. In addition, the following
    adverse reactions have been reported in connection with streptomycin:

    exfoliative dermatitis, systemic lupus erythematosus, purpura, skin
    sensitization via a cross reaction with neomycin, contact urticaria,
    post-operative respiratory depression, xanthopsia (disturbance of
    colour vision), anosmia (lack of olfactory perception), delirium,
    paranoid hallucinatory psychoses, agranulocytosis, serum sickness and
    anaphylaxis (Davies, 1991). 

    3.  COMMENTS

         The Committee considered data on pharmacokinetics, acute and
    short-term toxicity, teratogenicity, as well as special studies on
    ototoxicity and clinical studies, which were available on both
    compounds. In addition, chronic toxicity data and  in vitro
    microbiological data were available for dihydrostreptomycin. Two
    evaluation reports, as prescribed in the report of the fortieth
    meeting of the Committee (Annex 1, reference 104), on
    dihydrostreptomycin and streptomycin were also reviewed.

         Orally administered streptomycin and dihydrostreptomycin are
    poorly absorbed and most of the dose is recovered unchanged in the
    faeces in humans and domestic animals.

         After parenteral administration of either drug to laboratory or
    target animals, peak plasma levels are reached within about one hour.

         After parenteral administration of aminoglycosides to humans,
    including dihydrostreptomycin and streptomycin, antimicrobial activity
    is recovered in the urine, which accounts for approximately 80% of the
    administered dose.  However, no metabolites have been identified. The
    elimination half-life after therapeutic doses is 2 hours in adults,
    and 5-6 hours in neonates due to their lower glomerular filtration
    rate. Dihydrostreptomycin and streptomycin, in common with other
    amino-glycoside antibiotics, can be detected in the kidney after
    depletion from plasma. Detectable concentrations occur in urine for
    several weeks, suggesting accumulation of the drug in the kidney. 
    Accumulation also occurs in the perilymph of the inner ear and both
    streptomycin and dihydrostreptomycin are known to be ototoxic at
    therapeutic doses. The risk of ototoxicity is increased when renal
    function is compromised. 

         Placental transfer occurs and fetal serum concentrations range
    from 20-40% of maternal serum levels. 

         Single oral doses of dihydrostreptomycin and streptomycin salts
    were slightly toxic to experimental animals. LD50 values for
    dihydrostreptomycin in mice range from 12 500 mg/kg bw for the
    hydrochloride to > 30 000 mg/kg bw for the sulfate. For streptomycin,
    the oral LD50 in mice range from 8750 mg/kg bw for the calcium
    chloride complex to 25 000 mg/kg bw for the sulfate. 

         Parenteral administration of streptomycin at doses of 50-100
    mg/kg bw/day to dogs for 20 days resulted in renal damage within 1 to
    2 weeks, and 3 of 5 animals developed ataxia.  

         Ototoxicity was examined in a 90-day study in guinea-pigs treated
    orally with 40 mg dihydrostreptomycin/kg bw/day. Interpretation of the
    histopathological data was hampered by inadequate fixation of the

    cochlea; however, no hearing loss was reported in this study. In a
    subsequent 90-day study in cats treated orally with 40 mg
    dihydrostreptomycin/kg bw/day, no treatment-related effects were
    observed and vestibular function was normal. The NOEL was 40 mg/kg
    bw/day in this study.

         In a series of studies with streptomycin in monkeys, s.c.
    injection of 25 mg/kg bw/day for 66 days caused anaemia. After i.v.
    administration of 25-50 mg/kg bw/day in 3 divided doses for 5 days,
    transient impairment of hepatic function was observed. After
    parenteral administration (i.m., s.c., or i.v. injection) of 100-200
    mg/kg bw/day for 5 days, proteinuria was observed in addition to
    hepatic impairment. Parenteral doses of 25 mg/kg bw/day or more for 5
    days caused fatty changes in the liver and to a lesser extent in the
    kidney. There was no decrease in liver glycogen. These changes were
    reversible and had disappeared by 66 days after the last injection.

         No adverse effects were observed in target animal safety studies
    where cattle, sheep and pigs were treated i.m. with 30 mg/kg bw/day
    each of dihydrostreptomycin and penicillin G for 5 days (3 times the
    therapeutic dose) or 10 mg/kg bw/day of each drug for 15 days (3 times
    the recommended duration of treatment).

         Limited information was available on the genotoxicity of
    dihydrostreptomycin or streptomycin.  Streptomycin gave conflicting
    results in chromosomal aberration tests  in vitro. 

         In a 2-year toxicity study in rats, dihydrostreptomycin was
    administered in the diet to groups of 35 animals/sex/dose. Drug
    concentrations were adjusted weekly to give dose levels of 1, 5, or 10
    mg/kg bw/day. Interim sacrifices of 5 animals/sex/dose were made at 6
    and 12 months; the remaining 25 animals were administered
    dihydrostreptomycin for 2 years. After 6 months a slight, but not
    dose-related decrease in body-weight gain was observed in all treated
    males. At 18 months and 2 years body weights were slightly decreased
    in males of the group dosed with 10 mg/kg bw/day. At 2 years the
    incidence of tumours in treated groups was no higher than in control
    animals.  Twelve to 17 out of 25 animals in the treatment groups
    survived up to 2 years. Although this study did not meet current
    standards regarding the number of animals used, the Committee
    concluded that it represented an adequate test of the carcinogenic
    potential of the compound. The NOEL was 5 mg/kg bw/day based on
    decreased body weight in males at the high dose.

         The Committee concluded that the question of carcinogenic
    potential of streptomycin had been satisfactorily assessed in the
    2-year oral study with dihydrostreptomycin in rats, since the chemical
    structure, pharmacokinetic properties, and toxicity profile of the two
    compounds are almost identical.

         A number of studies were available in which pregnant mice were
    treated parenterally with streptomycin at doses up to 250 mg/kg bw/day
    on various days covering gestation days 9 to 16. In the F1 animals,
    body weights were reduced in both sexes at the lowest dose, and
    vestibular function was impaired at the highest dose. Streptomycin
    crossed the placental barrier and was identified in tissue fluids of
    embryos from treated dams. There was no effect on litter size, and no
    fetal malformations were observed at any dose. 

         Daily i.m. injection of either dihydrostreptomycin or
    streptomycin to pregnant guinea-pigs at doses of 25-200 mg/kg bw/day
    caused abortions or death. No abortions were produced with either drug
    at a dose of 10 mg/kg bw/day. There was evidence of placental damage
    at this dose level with both compounds, but no teratogenic effects
    were produced. Vestibular and auditory function were normal in F1
    animals.

         No teratogenic effects were observed in pregnant rabbits treated
    orally with 5 or 10 mg dihydrostreptomycin/kg bw/day on days 6-18 of
    gestation. However, no maternal toxicity was observed at these doses,
    indicating that the dose levels may not have been high enough to fully
    exclude teratogenic potential. 

         A literature review was available on pregnancy outcomes in women
    receiving streptomycin or dihydrostreptomycin parenterally for
    tuberculosis. The dose administered, where stated, was between 1-2 g
    daily or twice weekly, with total doses ranging from 2-202 g. Other
    drugs were administered concomitantly for tuberculosis in 162 cases.
    The only abnormalities observed were of the inner ear in 35/207
    infants (a rate of approximately 1 in 6). These consisted of
    vestibular dysfunction and varying degrees of hearing loss. Hearing
    loss occurred in the high-frequency range first, i.e. before the
    frequencies associated with normal speech were affected. 

         The Committee considered that the data in animals and humans
    indicated that the effects of dihydrostreptomycin and streptomycin on
    the middle ear of fetuses were a manifestation of fetotoxicity. The
    Committee concluded that these compounds were not teratogens.

         No studies were available on either compound on fertility or
    peri-/postnatal effects.  Dihydrostreptomycin has been used in
    veterinary medicine to preserve semen, for intra-uterine treatment of
    infections, and for the treatment of orchitis. In these situations, no
    adverse effects on reproduction have been reported. However, these
    data did not adequately address the potential for effects on fertility
    and reproduction.

         Minor renal tubular dysfunction, such as urinary casts and minor
    degrees of albuminuria occurs occasionally in humans treated with
    streptomycin. However, severe renal damage (proximal tubular necrosis)
    is rare and renal damage is usually reversible on cessation of
    therapy.  

         In a study in dogs, a dose equivalent to 50 g
    dihydrostreptomycin/kg bw/day caused a change in the intestinal flora
    after 15 days of treatment from susceptible lactose fermenting
    coliforms to a resistant population. The Committee considered that
    this study was not appropriate for extrapolation to effects in human.
    The dog was considered to be a more sensitive species than humans for
    these effects because of its shorter intestinal length compared to
    body mass, and reduced potential for dilution of intestinal contents
    with other food, intestinal secretions and intestinal epithelial
    cells. 

         The spectrum of antimicrobial and biological activity is similar
    for dihydrostreptomycin and streptomycin. Therefore results of
     in vitro antimicrobial activity studies on dihydrostreptomycin were
    also applied to streptomycin to calculate the upper limit of a
    potential ADI for combined residues of both compounds as follows:

    
                        Concentration without  x  Daily faecal Bolus (g)
                        effect on human gut
    Upper limit         flora (g/ml)a
    of ADI         =                                                                   

                        Fraction of oral       x  Safety factorc         x  Weight
                        dose available                                   of human
                        to gut florab                                    (60 kg)

                        32 g/ml x  150 g
                   =                         
                        1  x  1  x  60 kg

                   =    80 g/kg bw.

    a    The MIC values measured at high cell density (1 x 107 cells/spot) and under
         anaerobic conditions were considered to be more representative of conditions 
         occurring in the human gut than those measured at lower cell density 
         (1 x 105 cells/spot). Data were available on 17 species, including the 10 most 
         common genera of human intestinal microbes, with 5-11 strains tested per species. 
         The most sensitive species was  Bifidobacterium spp. An MIC50 value of 32 g/ml 
         (equivalent to 32 g/g) was selected as the concentration without effect on the 
         human gut flora.

    b    A conservative estimate of 100% was selected as the fraction of orally ingested 
         residues of dihydrostreptomycin and streptomycin available to the colonic microflora, 
         since no information was available on binding of drug residues to gut contents. 

    c    Because the colonic flora are relatively stable and variability within a particular
         individual may be as great as variability between individuals, and because it was 
         recognised that other values selected for this calculation were conservative and 
         already incorporated an adequate margin of safety, a safety factor of 1 was selected 
         to cover fully the variability between humans.
    
    4.  EVALUATION

         Dihydrostreptomycin and streptomycin are closely related in
    structure. Their pharmacokinetic properties, toxicological profiles,
    and spectrum of antimicrobial and biological activity are similar and
    therefore data on the two compounds have been considered together for
    the purpose of establishing a single ADI.

         The most sensitive effects in all of the available studies on
    dihydrostreptomycin and streptomycin were those observed with
    dihydrostreptomycin in the two-year oral toxicity study in rats, where
    the NOEL was 5 mg/kg bw/day.  Based on this NOEL and using a safety
    factor of 200, the Committee established a temporary ADI of 30 g/kg
    bw for the combined residues of both dihydrostreptomycin and
    streptomycin.

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    See Also:
       Toxicological Abbreviations
       STREPTOMYCIN (JECFA Evaluation)