First draft prepared by Gladwin Roberts¹ & Carl Cerniglia^2
1Chemical Products Assessment Section, Therapeutic Goods Administration, Department of Health and Aged Care, Canberra, Australia; and
²National Center for Toxicological Research, Food and Drug Administration, Arkansas, USA

Cefuroxime is a cephalosporin antibacterial agent with activity against a range of gram-positive and gram-negative bacteria. The chemical name of cefuroxime sodium is sodium (Z)-(6R,7R)-3-(carbamoyloxymethyl)-7-[2-(2-furyl)-2-(methoxy-imino)acetamide]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate. Its structure is shown in Figure 1. The sodium salt is used in veterinary medicine for the treatment of mastitis and is available in two formulations, both applied by intramammary infusion: one for the treatment of clinical mastititis in lactating cattle and the second for the treatment of sub-clinical mastitis in dry cows and to prevent new infections during the dry period. Cefuroxime is also used in human medicine, as either the sodium salt or as the 1-acetoxyethyl ester (known as cefuroxime axetil).

Cefuroxime has not previously been evaluated by the Committee.

2.1.1 Absorption, distribution and excretion

Rats

Groups of three Wistar rats were given [¹⁴C]cefuroxime sodium as a single intravenous or intramuscular injection of 25 mg/kg bw or as an intravenous infusion of 50 mg/kg bw over 40 min. The blood concentrations of radiolabel were highest within 30 min of the end of administration and then rapidly declined, with initial half-times of 0.5–1 h. By 24 h, the blood concentrations were < 10% of the respective peak. It was distributed widely, kidney and liver having higher concentrations of radiolabel than blood; particularly low concentrations were detected in the central nervous system, muscle and fat. Dosing of female rats on day 18 of gestation resulted in very low concentrations of radiolabel in fetal tissue and amniotic fluid. Relatively high concentrations were detected in the milk of lactating rats, and the peak represented 18% of blood concentrations after 1 h. About 80% of a parenteral dose was excreted in urine, and the remainder was excreted in bile, predominantly during the first 24 h. A portion of the radiolabel in bile was subject to enterohepatic recirculation. Daily intramuscular injections for up to 14 days did not affect the kinetics in blood or excretion in urine (Nanbo et al., 1979; Okumura et al., 1979).

In anaesthetized rats given a single intravenous injection of 20 mg/kg bw of cefuroxime, the bioavailability in brain was 4.2% that in plasma, thus confirming the low penetration of the blood–brain barrier (Tsai et al., 1999).

The absorption of cefuroxime axetil in the small intestine of anaesthetized rats was investigated in situ by perfusion at a concentration of 12, 59, 120 or 200 µmol/l. Absorption across the intestinal mucosa appeared to occur as a result of an active transport mechanism. Some drug was hydrolysed in the lumen of the intestine, the proportion increasing from 16 to 25% with increasing concentration (Ruiz-Balaguer, et al., 1997).

In seven rats given a single dose of 2 mg of cefuroxime axetil by gavage, the peak plasma concentration of cefuroxime was found at about 30 min. About 25–30% of the dose was bioavailable, and a similar amount was considered to have been immediately excreted in the bile. The relatively low bioavailability appears to be due to hydrolysis in the intestine, which reduces the amount of the ester available for absorption, and hydrolysis in blood, which facilitates rapid excretion of cefuroxime in the urine (Ruiz-Carretero et al., 2000).

Rabbits

Groups of four rabbits were given single intravenous or intramuscular injections or twice daily intramuscular injections of cefuroxime at a dose of 25 mg/kg bw for 15 days. The peak blood concentrations were reached within 15 min after each administration and then rapidly declined. About 75–80% of the drug was recovered in urine within 24 h. No cefuroxime was detected in organs 24 h after the final dose (Okumura et al., 1979).

Dogs

Three male beagle dogs were given a single intravenous injection of 25 mg/kg bw [¹⁴C]cefuroxime sodium. The concentration of radiolabel in blood peaked immediately after dosing and then decreased, with an initial half-time of 0.7 h. About 90% of the dose was excreted in urine; recovery of about 8% in faeces suggested limited excretion in bile (Nanbo et al., 1979). In beagle dogs given an intramuscular dose of 25 mg/kg bw cefuroxime, 4% of the dose was detected in bile; the concentrations were maximal 1–2 h after administration and gradually decreased thereafter up to 24 h (Okumura et al., 1979).

Plasma was taken from one male and one female beagle dog given cefuroxime axetil by gavage at a dose of 100, 400 or 1600 mg/kg bw per day. Samples were withdrawn after treatment for 1, 36, 169 and 188 days. Peak concentrations of cefuroxime in plasma were found within 2 h of administration, and the bioavailability was claimed to be proportional to the dose. Unchanged cefuroxime axetil was also detected in the plasma of the female given 400 mg/kg bw per day and in both animals at 1600 mg/kg bw per day, attaining a highest concentration representing about 10% of the peak. De-esterification led to formation of acetaldehyde and acetic acid (Spurling et al., 1986).

Humans

Cefuroxime sodium was poorly absorbed through the gastrointestinal tract. After oral administration of 1000 mg to two volunteers, only 1% of the administered dose was recovered in urine, and the plasma concentrations were stated to be only just measurable. When cefuroxime sodium was injected, at least 95% of the dose was recovered in the urine, mainly in unchanged form (Foord, 1976).

Cefuroxime is widely distributed in the body, entering body fluids and tissues when given at therapeutic concentrations. It crossed the placenta and has been detected in breast milk (Parfitt, 1999). The concentrations of cefuroxime in cerebrospinal fluid were about 10% of those in plasma (Mandell & Petri, 1996). Injection of 750 mg of cefuroxime to women during pregnancy, labour or caesarean section resulted in significant concentrations in the amniotic fluid and umbilical blood vessels and in plasma from the neonates (Craft et al., 1981; Phillipson & Stiernstedt, 1982).

Moderate amounts of cefuroxime axetil were absorbed after five oral doses of 125, 250, 500 × 2 and 1000 mg to 12 male volunteers. The bioavailability was about 36% in fasted individuals and 50% after food intake. A linear relationship was found between the dose in fed subjects and both the area under the plasma concentration–time curve and the peak plasma concentration. The peak plasma concentration was 43% greater in fed subjects than in fasted subjects (Finn et al., 1987). Cefuroxime axetil was hydrolysed in the intestinal mucosa and blood to yield cefuroxime; the resulting concentrations in plasma were variable (Parfitt, 1999). The plasma half-time was 1–2 h, the maximum plasma concentration after oral administration was 6.3 mg/l, and the degree of protein binding was 33–50% (Kalman & Barriere, 1990). Cefuroxime was excreted primarily in urine (Williams & Harding, 1984), and secretion by the renal tubules was responsible for 43–54% of the renal elimination (Foord, 1976). The kinetics was unaffected by repeated oral dosing for 7 days (Sommers et al., 1984).

2.1.2 Biotransformation

Rats and dogs

Up to 97% of administered [¹⁴C]cefuroxime sodium remained unchanged in the plasma and urine of rats and dogs treated parenterally. However, an unidentified metabolite was detected in the bile of rats, which accounted for about 27% of the material present, the remainder being unchanged parent drug (Nanbo et al., 1979). In another study, in rats given cefuroxime by intramuscular injection, thin-layer chromatography showed that the only compound present in urine, bile and plasma was the parent. The metabolites produced in rats and dogs were not identified (Okumura et al., 1979).

Humans

Cefuroxime axetil mixed with human blood in vitro was rapidly de-esterified to cefuroxime, with a half-time of 3.5 min. Similarly, in 12 male volunteers given a single oral dose of 1.5 g of cefuroxime axetil, hydrolysis of the ester was virtually complete, and cefuroxime was the only compound detected in blood (Harding et al., 1984). In 11 children given a single oral dose of 10, 15 or 20 mg/kg bw cefuroxime axetil, the unchanged ester was found in the urine of only four subjects and accounted for < 0.1% of the administered dose (Powell et al., 1991).

2.2.1 Acute toxicity

The studies of acute toxicity did not comply with good laboratory practice (GLP). As shown in Table 1, cefuroxime was of low acute toxicity in mice and rats after oral or parenteral administration and was slightly toxic in rabbits when administered parenterally.

The only adverse effect seen after oral administration was diarrhoea. In animals that died after parenteral injection, swelling of the caecum was the main effect seen at autopsy, and destruction of cortical renal tubules was observed only in rats (Tamura et al., 1979).

Two cats and four dogs were given a single intramuscular injection of 2 g/kg bw cefuroxime sodium as a 40% solution in water. No signs of toxicity were seen, and the only treatment-related effect was discomfort at the injection site, which persisted for a few minutes after injection. Cynomolgus monkeys given 1.5–2.0 g/kg bw intramuscularly showed slight loss of body weight, and some had diarrhoea (Glaxo Laboratories Ltd, 1986; Capel-Edwards et al., 1979).

2.2.2 Short-term studies of toxicity

Rats

A series of studies that did not comply with GLP were conducted in rats given cefuroxime sodium parenterally.

Groups of five male and five female CD rats received cefuroxime sodium in 0.9% saline solution intravenously at a dose of 0, 50, 100, 200 or 400 mg/kg bw per day for 29 (males) or 30 (females) days. Treatment had no effects on body weight, general condition, haematological, blood biochemical or urinary end-points, organ weights or lesions. As only a summary of this study was available, the absence of findings could not be confirmed independently (Glaxo Laboratories Ltd, 1986).

Groups of eight male and eight female Charles River CD rats were given cefuroxime sodium in 0.9% saline solution by subcutaneous injection at a dose of 0, 100, 200, 400 or 800 mg/kg bw per day for 33 (males) or 34 (females) days. There were no toxic signs, no effects on body-weight gain and no changes in urinary parameters. Inflammation and ulceration at the injection site were noted in animals at the highest dose. Haemoglobin concentration and erythrocyte volume fraction were reduced in some animals given 200 mg/kg bw per day or more, although the effect was significant only at the highest dose. The serum potassium concentration was increased in females at 100 and 800 mg/kg bw per day. Lymphatic dilatation and lymphocyte infiltration were seen in the colonic mucosa in some animals at 800 mg/kg bw per day. There were no significant effects at 100 mg/kg bw per day. As only a summary of this study was available, the absence of findings cannot be confirmed independently (Glaxo Laboratories Ltd, 1986).

Groups of 18 male and 18 female SD-JCL rats were given cefuroxime in distilled water by subcutaneous injection at a dose of 200, 500 or 1500 mg/kg bw per day on 6 days per week for 35 days. A similar group of controls was given saline. An additional group of six males and six females given the highest dose was retained for a 5-week recovery period after the end of treatment. No deaths or signs of overt toxicity were noted, and there were no effects on body-weight gain, water intake or urinary end-points. A significant fall in erythrocyte count was seen in males at the highest dose and in females at all doses. Significant decreases in haemoglobin concentration and erythrocyte volume fraction were noted in animals of each sex given the highest dose. An increase in leukocyte numbers occurred in males a 500 or 1500 mg/kg bw per day.

Increased serum alanine aminotransferase activity was seen in animals of each sex at 1500 mg/kg bw per day and increased alkaline phosphatase activity in males at 500 and 1500 mg/kg bw per day. Bilirubin concentrations were decreased in all groups of treated males and in females at 500 and 1500 mg/kg bw per day. A significant increase in blood glucose concentration was seen in males at the two higher doses, while significant decreases were seen in all groups of treated females. The albumin concentration was decreased and the potassium concentrations were increased in animals at 1500 mg/kg bw per day. At this dose, males showed decreased liver weights. The weight of the kidney was increased in males, and caecal swelling was seen in animals of each sex at the two higher doses of cefuroxime. All the changes were fully or partially reversed on cessation of dosing. No compound- related effects were found on histological examination. A NOEL was not identified (Ito et al., 1979a).

Groups of 18 male and 18 female SD-JCL rats were given cefuroxime in distilled water by intraperitoneal injection at a dose of 100, 300 or 1000 mg/kg bw per day on 6 days per week for 35 days. A similar group of controls was given saline. An additional group of six males and six females at the highest dose was allowed a 5-week recovery period after the end of treatment. No deaths or signs of overt toxicity were noted, and there were no effects on body-weight gain or urinary end-points. Females at 1000 mg/kg bw per day had slightly increased water intake. Erythrocyte counts were significantly decreased in males at the highest dose, and increased values were found in females at 300 and 1000 mg/kg bw per day. The haemoglobin concentration and erythrocyte volume fraction were not affected. Blood glucose concentrations were decreased in males and blood urea nitrogen concentrations were decreased in females at 300 and 1000 mg/kg bw per day but with no dose–response relationship. The potassium concentration was decreased in females at 300 and 1000 mg/kg bw per day and increased in males at 100 and 1000 mg/kg bw per day. Caecal swelling was noted in animals at 300 and 1000 mg/kg bw per day. There were no compound-related effects on organ weights or on histological appearance. All changes were reversed on cessation of dosing. There were no significant effects at 100 mg/kg bw per day (Ito et al., 1979a).

Groups of seven male and seven female CD rats were given cefuroxime sodium in 0.9% saline by subcutaneous injection at a dose of 0, 100, 300 or 900 mg/kg bw per day for 91 days. The groups given the control and highest dose contained an additional seven rats of each sex which were allowed a 21-day recovery period at the end of dosing. There were no effects on general condition, blood biochemistry or body weight. The groups given 300 and 900 mg/kg bw per day showed reduced erythrocyte count, haemoglobin concentration and erythrocyte volume fraction. Reticulocyte counts were slightly increased in male rats that had reduced erythrocyte counts. Total leukocyte counts were increased in females at the two higher doses, but the differential counts were unaffected. Prothrombin times were slightly increased in animals of each sex given the highest dose and in males at 300 mg/kg bw per day. Urine volume, urinary electrolyte excretion and water intake were increased and specific gravity decreased in animals at 900 mg/kg bw per day. The spleen weight was increased in females at 900 mg/kg bw per day, but the only pathological findings were inflammation, haemorrhage and haemosiderin deposition at the injection sites in rats at 300 and 900 mg/kg bw per day. The changes were reversed at the end of the recovery period. There were no significant effects at 100 mg/kg bw per day. As only a summary of this study was available, the findings cannot be confirmed independently (Glaxo Laboratories Ltd, 1986).

Groups of 10 male and 10 female CD rats were given cefuroxime sodium in 0.9% saline by subcutaneous injection at a dose of 0, 50, 150 or 450 mg/kg bw per day for 26 weeks. Body-weight gain and general condition were unaffected, except for localized swelling at the injection site. There were slight reductions in erythrocyte volume fraction, haemoglobin concentration and erythrocyte counts, and increases in reticulocyte counts in animals at 450 mg/kg bw per day. The serum protein concentration was slightly decreased and sodium and potassium excretion was increased in animals at 450 mg/kg bw per day. The only pathological changes were those associated with physical damage and inflammatory reactions at the injection site. There were no significant effects at 150 mg/kg bw per day. As only a summary of this study was available, the findings cannot be confirmed independently (Glaxo Laboratories Ltd, 1986).

Groups of 26 male and 26 female SD-JCL rats were given cefuroxime in distilled water by subcutaneous injection at a dose of 100, 250 or 750 mg/kg bw per day on 6 days per week for up to 26 weeks. Similar groups of controls were given saline. Animals were killed after 3 months (eight rats of each sex) and 6 months (10 rats of each sex) of treatment, and after a 3-month recovery period (eight rats of each sex). There were no overt signs of toxicity and no significant effects on urinary end-points. Body-weight gain was slightly depressed in males at 750 mg/kg bw per day despite a small increase in food intake. Erythrocyte count, haemoglobin concentration and erythrocyte volume fraction were lower in females at all doses. Significant decreases were seen in serum aspartate aminotransferase activity in males at all doses and in females at 750 mg/kg bw per day and in bilirubin concentration in males at 250 mg/kg bw per day and in males and females at 750 mg/kg bw per day. Slight decreases in cholesterol, total protein and albumin concentration were seen in rats at the highest dose. Kidney weights were increased in the groups given 250 or 750 mg/kg bw per day, but the effect was not associated with pathological alterations. Caecal swelling was seen in animals of each sex at 250 and 750 mg/kg bw per day after 3 and 6 months of treatment. None of these changes was seen at the end of the recovery period. A NOEL was not identified (Ito et al., 1979b).

Groups of 26 male and 26 female SD-JCL rats were given cefuroxime in distilled water by intraperitoneal injection at a dose of 50, 125 or 375 mg/kg bw per day on 6 days per week for 26 weeks. A similar group of controls was given saline. Animals were killed after 3 months (eight rats of each sex) and 6 months (10 rats of each sex) of treatment and after a 3-month recovery period (eight rats of each sex). There were no overt signs of toxicity and no deaths that could be attributed to treatment. Body-weight gain was unaffected; however, feed conversion was reduced at 3 months in animals at 125 or 375 mg/kg bw per day, gradually returning to control levels thereafter. There were no effects on urinary parameters. Leukocyte counts were decreased in females at 125 and 375 mg/kg bw per day; at the highest dose, this effect was associated with an increase in the ratio of neutrophils to lymphocytes. A decreased total protein concentration in males at the highest dose was the only consistent biochemical alteration. Caecal swelling was seen in animals of each sex at 375 mg/kg bw per day at 3 months only, but no histopathological findings were attributable to administration of the compound. The leukocyte counts remained low during the recovery period, whereas all other changes were reversed to control levels. No effects were seen at 50 mg/kg bw per day (Ito et al., 1979b).

Dogs

A series of studies that did not conform to GLP were conducted, in which dogs were treated with cefuroxime sodium parenterally and with cefuroxime axetil by oral administration.

Groups of two male and two female beagle dogs were given cefuroxime sodium in 0.9% saline by intramuscular injection at a dose of 0, 60, 180 or 540 mg/kg bw per day for 10 or 11 days. All the dogs gained weight and remained in good health. Haematological, blood biochemical and urinary end-points were unremarkable. The weights of the liver and kidney relative to body weight were increased at 540 mg/kg bw per day, but the lesions were limited to irritation at the injection site. As only a summary of this study was available, the findings cannot be confirmed independently (Glaxo Laboratories Ltd, 1986).

Groups of three male and three female beagle dogs were given cefuroxime sodium in saline by subcutaneous injection at a dose of 0, 50 or 500 mg/kg bw per day on 6 days per week for 5 weeks. One animal of each sex per group was allowed a 4-week recovery period at the end of treatment. No overt toxicity was seen, but body-weight loss was seen in male dogs at 500 mg/kg bw per day. Haematological and urinary analyses revealed no significant findings. The bilirubin concentration was decreased in both groups of treated males, but the difference was seen before the beginning of dosing. Organ weights and gross appearance were unaffected. At the end of the recovery period, the end-points in control and treated animals were similar. No effects were seen at 50 mg/kg bw per day (Ito et al., 1979c).

Groups of three male and three female beagle dogs were given cefuroxime sodium in saline by intravenous injection at a dose of 0, 25 or 250 mg/kg bw per day on 6 days per week for 5 weeks. One animal of each sex per group was allowed a 4-week recovery period at the end of treatment. Body-weight loss was observed in males at the higher dose. There were no signs of overt toxicity and no effects on haematological, blood biochemical or urinary end-points, organ weights or histopathological appearance. At the end of the recovery period, all parameters were similar in control and treated animals. No effects were seen at 25 mg/kg bw per day (Ito et al., 1979c).

Cefuroxime axetil was administered as an aqueous suspension to groups of four male and four female beagle dogs twice daily by gavage for 27 weeks. The equivalent doses of cefuroxime were 0, 100, 400 and 1600 mg/kg bw per day. Additional groups of two males and two females given 0 or 400 mg/kg bw per day were allowed a 3-week recovery period. Two dogs were killed during the study because of intercurrent disease (polyarteritis). The only signs seen in the remaining animals were occasional vomiting and salivation at the highest dose. Body-weight gain was slightly retarded in the group at this dose. Ophthalmic, electrocardiographic and urinary parameters were unaltered. At the highest dose, erythrocyte count, haemoglobin concentration and erythrocyte volume fraction were lower and the reticulocyte number was higher than in controls. Prolonged prothrombin and activated partial thromboplastin times were observed in males at 1600 mg/kg bw per day, and the concentration of coagulation factor VII was reduced in this group. Plasma total protein, albumin and cholesterol concentrations were reduced and that of triglycerides increased at 1600 mg/kg bw per day. The weight of the kidneys of males at this dose was increased. No differences were seen between groups after the recovery period. None of the macroscopic or microscopic findings was attributable to treatment. The NOEL was 400 mg/kg bw per day (Spurling et al., 1986).

Groups of three male and three female beagle dogs were given cefuroxime sodium by subcutaneous or intramuscular injection at a dose of 0, 50, 150 or 450 mg/kg bw per day for 6 months. The route of administration was varied during the study to minimize the irritating effects of the injections. The compound was initially given in saline, but distilled water was used as the vehicle from day 25. Controls and dogs at 50 mg/kg bw per day were given intramuscular injections into the hind legs, while animals at the higher doses received subcutaneous injections.

After 12 weeks of treatment, one animal at the highest dose developed a Heinz body haemolytic anaemia and was killed after a further 2 weeks. Otherwise, the condition and body-weight gain of dogs was generally good throughout the study. Discomfort arose at the site of injection, particularly after the subcutaneous doses. The mean corpuscular haemoglobin concentrations were slightly reduced in dogs at 150 and 450 mg/kg bw per day. Serum iron values were consistently reduced (significant after 8 weeks), and serum iron binding capacity was increased in animals at the highest dose throughout the study. Analyses of blood biochemistry, urine and organ weights showed no compound-related effects. The only pathological changes were inflammatory reactions at the injection sites in some treated dogs and changes to the bone marrow and reticuloendothelial system consistent with severe haemolytic anaemia in the animal killed at week 14. No effects were seen at 50 mg/kg bw per day. As only a summary of this study was available, the findings could not be confirmed independently (Glaxo Laboratories Ltd, 1986).

Monkeys

In a study that did not comply with GLP, groups of two male and two female cynomolgus monkeys were given cefuroxime sodium in 0.9% saline by intramuscular injection at a dose of 0, 150 or 450 mg/kg bw per day for 28 days. No overt signs of toxicity were seen, although some animals in each treated group produced softer faeces than normal for a few days at the beginning of treatment. Animals at 450 mg/kg bw per day showed transient reductions in erythrocyte count and haemoglobin concentration (significant at day 7), with moderate leukocytosis (neutrophilia and eosinophilia) in males only. These changes had largely reversed by the end of the study. Blood biochemistry and urinary parameters showed no alterations, and there were no compound-related effects on organ weights. Histological examination revealed only inflammatory reactions at injection sites. As only a summary of this study was available, the findings cannot be confirmed independently. A NOEL was not identified (Glaxo Laboratories Ltd, 1986).

2.2.3 Genotoxicity

A battery of tests that complied with appropriate standards was conducted to address the genotoxicity of cefuroxime sodium. The results are summarized in Table 2.

As expected, cefuroxime was toxic to the bacterial strains used in the mutagenicity assays. Consequently, only relatively low concentrations of cefuroxime sodium could be tested in these studies. The selected concentrations were based on the results of tests for cytotoxicity. Negative results were obtained, except in the test for induction of chromosomal aberrations in cultured human peripheral blood lymphocytes obtained from one woman and one man. In this test, a positive result was seen in the absence of the metabolizing system. Prolonged exposure, for 20–44 h, was required to obtain a positive effect, and no chromosomal damage was observed after exposure for 3 h. The aberrations were predominantly chromatid deletions, with very few chromosome rearrangements. Although the aberration frequencies were markedly higher than in controls, the magnitude of the response was less than proportional to the concentration of cefuroxime. This may have been due to inhibition of mitosis, which increased from 14% to 54% as the concentration was increased. Nevertheless, these positive results obtained in vitro were not confirmed in a test for micronucleus formation in vivo in mice receiving cefuroxime sodium at intraperitoneal doses of up to 10 000 mg/kg bw.

Similar clastogenic effects were seen in cultured human lymphocytes treated with two other cephalosporins, cephalonium (Marshall, R., 1995) and cephalexin (Riley, 1996). Another cephalosporin, ceftiofur sodium, did not induce reverse mutation in bacteria, mutations in mammalian cells in vitro or micronuclei in vivo. However, chromosomal damage was seen in Chinese hamster ovary cells after exposure in vitro for 44 h, but not for shorter times (Aaron et al., 1995a). These data on ceftiofur were reviewed by the Committee at its forth-fifth meeting and were considered to be of no biological significance (Annex I, reference 120). Further investigations suggested that the clastogenic effect of ceftiofur is associated with inhibition of cell division (Aaron et al., 1995b).

2.2.4 Reproductive toxicity

A series of studies that did not conform to GLP were conducted with parenteral administration of cefuroxime sodium.

(a) Multigeneration studies

Mice

Groups of 12 male and 30 female CRH mice were given cefuroxime sodium in distilled water by subcutaneous injection at a dose of 800, 1600 or 3200 mg/kg bw per day. Controls were given 0.9% saline. After 60 days, each male was caged with two or three female mice at the same dose When pregnancy was detected, the female mice were re-housed. When most of the female mice were pregnant, the males were killed. The females were divided into two approximately equal groups per dose: one group was killed on day 18 of gestation, and the females in the other group were allowed to deliver and rear their litters. The latter group received their final dose on day 18 of gestation. Three weeks after the birth of the F₁ pups, the F₀ dams and all but one male and one female from each litter were killed. When the F₁ pups were 4 weeks old, one male from one litter was selected and re-housed with one female from another litter to give rise to the F₂ generation. The F₁ dams and the F₂ pups were killed on postnatal day 21.

The only treatment-related sign during the study was subcutaneous swelling at the site of injection. There were no treatment-related effects on body-weight gain, conception rate, numbers of implantation sites or resorptions, numbers of live fetuses, litter weights or the proportions of male mice in either generation. There were no fetal abnormalities, and the body-weight gain and physical development of the pups was unaffected. No reproductive effects were observed at any dose (Griffiths, 1975a).

Rats

Groups of 20 male and 20 female Sprague-Dawley rats were given cefuroxime sodium in physiological saline by subcutaneous injection at a dose of 0, 200, 400 or 800 mg/kg bw per day. Males were treated from 60 days before and during mating, while females were treated from 14 days before mating until day 7 of gestation. The dams were killed on day 20 of gestation. Pain during drug administration was noted in animals given the highest dose. Males at doses of 400 mg/kg bw per day and above showed slight increases in food intake, and water intake was increased in all treated groups. Body-weight gain was suppressed in treated females during the latter part of gestation. There were no differences in conception rates or in the numbers of corpora lutea, implantations, resorptions or live fetuses. Fetal body weights and the numbers of malformed fetuses were not influenced by treatment. Neither fertility nor reproduction was affected at any dose (Otaka et al., 1979).

(b) Developmental toxicity

Mice

Groups of 10–17 pregnant female CRH mice were given subcutaneous injections of cefuroxime sodium in 0.9% saline solution at a dose of 0, 800, 1600, 3200 or 6400 mg/kg bw per day on days 6–15 of gestation and killed on day 18 of gestation. The animals remained in good condition, and there were no effects on body-weight gain or the numbers of implantation sites, resorptions or live fetuses. Litter weights and the sex ratio of fetuses were unaffected, and no fetal abnormalities were noted. Fetal development was not affected at any dose (Troughton & Bartholomew, 1975a).

Rats

Groups of 30 pregnant Sprgaue-Dawley rats were given cefuroxime sodium in physiological saline by subcutaneous injection at a dose of 0, 200, 400, 800 or 1600 mg/kg bw per day on days 7–17 of gestation. Twenty females in each group were killed on day 20 of gestation, and the remaining 10 were allowed to deliver and rear their pups for 21 days. Dams in the latter groups were killed on postnatal day 21, and the F₁ offspring matured up to 10 weeks of age. One male and two female F₁ rats per dam in each treatment group were mated; one of the two females was killed on day 20 of gestation, and the other was allowed to deliver and rear the F₂ pups for 3 weeks. Pain, bleeding and haematomas at the injection site were common at the highest dose. Dams in all groups showed slight depression in body-weight gain and increased water intake and caecal weight. In the phase at which teratogenesis was examined, lower body weights were seen in F₁ fetuses at 800 and 1600 mg/kg bw per day, but this effect was not seen in full-term pups. No effects were found on the numbers of implantations, resorptions or live fetuses, sex ratios, the incidences of fetal abnormalities or postnatal development or reproductive capacity in either generation. There were no effects on fetuses at 400 mg/kg bw per day (Otaka et al., 1979).

Groups of 30 pregnant Sprgaue-Dawley rats were given cefuroxime sodium in physiological saline by intravenous injection at a dose of 0, 200, 400 or 800 mg/kg bw per day on days 7–17 of gestation. Twenty females in each group were killed on day 20 of gestation, and the remaining 10 were allowed to deliver and rear their pups for 21 days. Dams in the latter groups were killed on postnatal day 21, and the F₁ offspring matured up to 10 weeks of age. One male and two female F₁ rats per dam in each treatment group were mated; one of the two females was killed on day 20 of gestation, and the other was allowed to deliver and rear the F₂ pups for 3 weeks. Twitching after injection was noted at doses of 400 mg/kg bw per day and above. Slight depression in body-weight gain was seen in dams at the highest dose and increased water intake and caecal weight in all treated groups. No effects were found on the numbers of implantations, resorptions or live fetuses, sex ratios, the incidences of fetal abnormalities or postnatal development or reproductive capacity in either generation. There were no effects on fetuses at any dose (Otaka et al., 1979).

Rabbits

Groups of 5–11 pregnant Dutch rabbits were given cefuroxime sodium in 0.9% saline by intramuscular injection at a dose of 0, 50, 100, 200 or 400 mg/kg bw per day on days 6–18 of gestation and were killed on day 29 of gestation. Four does given 400 mg/kg bw per day, one given 200 mg/kg bw per day and one given 100 mg/kg bw per day died during the study. The rabbits developed diarrhoea before death, probably due to disturbances of the gut flora. Surviving does showed no effects on body-weight gain, and there were no effects on the numbers of implantation sites, resorptions or live fetuses. The incidence of fetal abnormalities was similar in all groups. Fetal development was not affected at any dose (Troughton & Bartholomew, 1975b).

Groups of 10 pregnant New Zealand white rabbits were given cefuroxime sodium in physiological saline by intravenous or subcutaneous injection at a dose of 0, 25, 50, 100 or 150 mg/kg bw per day on days 6–18 of gestation and were killed on day 28 of gestation. No deaths occurred during the study, and the body weights were similar to those of controls. Caecal weight was increased in does at the highest dose. No differences were seen in the numbers of implants, resorptions or live fetuses, in the sex ratio, in fetal weights or in the incidences of fetal abnormalities in any group. Fetal development was not affected at any dose (Furuhashi et al., 1979).

(c) Peri- and postnatal toxicity

Mice

Groups of 12–15 pregnant CRH strain mice were given cefuroxime sodium in 0.9% saline by subcutaneous injection at a dose of 0, 800, 1600 or 3200 mg/kg bw per day from day 16 of gestation to 23 days after parturition. The dams and pups were killed on postnatal day 23. The severity of local tissue damage at the injection site was dose-dependent. There were no effects on maternal body weight, length of gestation or sex ratio. The litter sizes were reduced at 1600 and 3200 mg/kg bw per day but with no dose–response relationship. Postnatal development of pups and the proportion of pups successfully weaned were unaffected. There were no effects on reproductive capacity at 800 mg/kg bw per day (Griffiths, 1975b).

Rats

Groups of 20 pregnant Sprague-Dawley rats were given cefuroxime sodium in physiological saline by subcutaneous injection at a dose of 0, 200, 400 or 800 mg/kg bw per day from day 17 of gestation to day 20 after parturition. The dams were killed on postnatal day 21. One male and two female F₁ offspring per dam in each group were mated at 10 weeks of age; one of the two females was killed on day 20 of gestation, and the other was allowed to deliver and rear the F₂ pups for 3 weeks. Body-weight gain and food and water intakes were increased in F₀ dams in all groups during lactation. No differences in gestation or parturition or in the numbers of implantations or live pups, sex ratios or body weights of offspring were found in any generation. Caecal weights at the time of weaning were increased in male and female F₁ pups of dams at 400 and 800 mg/kg bw per day. Pre- and postnatal development, fertility and reproductive capacity were unaffected at any dose (Otaka et al., 1979).

Rabbits

Groups of 10–16 pregnant Dutch rabbits were given cefuroxime sodium in 0.9% saline by intramuscular injection at a dose of 0, 50, 100 or 200 mg/kg bw per day from day 19 of gestation to 6 weeks after parturition. Surviving does and offspring were killed on postnatal days 42–44; however, several deaths occurred before parturition: one at the lowest dose, two at the intermediate dose and six at the highest dose. The deaths were attributed to perturbation of the maternal gut flora and secondary toxaemic effects on the liver. Another three does given 200 mg/kg bw per day either aborted or lost their entire litters soon after parturition. There were no effects on maternal body weight, length of gestation, sex ratio or litter size. The weights of pups of does at the highest dose were consistently low at parturition and throughout lactation, but their postnatal development and survival were unaffected. There were no effects on offspring of does at 100 mg/kg bw per day (Griffiths, 1975c).

2.2.5 Special studies

(a) Renal toxicity

Studies on nephrotoxic potential that did not comply with GLP were carried out in rats, rabbits and dogs.

Rats

Groups of 10 male and 10 female Sprague-Dawley JCL rats were given cefuroxime sodium in distilled water as a single injection, either subcutaneously at 0, 1000 or 3000 mg/kg bw or as intravenously at 0, 500 or 1500 mg/kg bw. It was not clear when the tests were conducted or when the animals were killed, but they were probably killed 24 h after treatment. The specific gravity and sodium and potassium content of urine were increased in females at 3000 mg/kg bw, and the urinary sodium concentration was decreased in males at this dose. Decreased blood concentrations of creatinine were seen in females, of potassium in males and of uric acid in males and females, all at 3000 mg/kg bw. The blood concentrations of magnesium in females at 1500 mg/kg bw and of urea nitrogen in both sexes at 500 and 1500 mg/kg bw were increased. Renal function tests and histopathological examination of a range of tissues revealed no treatment-related changes (Ito et al., 1979d).

Groups of 10 male and 10 female Sprague-Dawley JCL rats were given cefuroxime sodium in distilled water by subcutaneous injection at a dose of 0, 800 or 1600 mg/kg bw per day or by intravenous injection at 0, 400 or 800 mg/kg bw per day for 1 week. The results of urine analysis were unremarkable. At 1600 mg/kg bw per day given subcutaneously, the blood concentrations of glucose, protein and albumin were decreased in males, those of creatinine and uric acid were decreased in females, and that of sodium was increased in females. The blood urea nitrogen concentration was increased at both intravenous doses, and the blood concentrations of uric acid and sodium were increased at 800 mg/kg bw per day. Renal function tests and histopathological examination of a range of tissues revealed no treatment-related changes (Ito et al., 1979d).

Rabbits

Groups of five male and five female New Zealand white rabbits were given cefuroxime sodium in distilled water as a single intramuscular injection of 0, 100 or 300 mg/kg bw. It was not clear when the tests were conducted or when the animals were killed, but they were probably killed 24 h after treatment. The urinary chloride concentration was increased in females at both doses. Tests for blood biochemistry and renal function and histopathological examination of a range of tissues revealed no treatment-related changes (Ito et al., 1979d).

Groups of five male and five female New Zealand white rabbits were given cefuroxime sodium in distilled water by intramuscular injection at a dose of 0 or 100 mg/kg bw per day for 1 or 4 weeks. After 4 weeks of dosing, increased urine volume associated with decreased sodium, potassium and chloride concentrations were observed in treated females. Increased creatinine and phenolsulfonphthalein clearance were seen in females treated for 1 week but not in those treated for 4 weeks. Blood biochemical and histopathological examination of a range of tissues revealed no treatment-related changes (Ito et al., 1979d).

Dogs

Groups of three male and three female beagle dogs were given cefuroxime sodium in distilled water as a single intravenous injection of 0 or 1000 mg/kg bw. Urinary and blood analyses gave unremarkable results. Phenolsulfonphthalein clearance was increased in treated females. Histopathological examination of a range of tissues revealed no treatment-related changes (Ito et al., 1979d).

Groups of three male and three female beagle dogs were given cefuroxime sodium in distilled water by intravenous injection at a dose of 0, 250 or 500 mg/kg bw per day for 1 week. No treatment-related changes were found in the results of urinary analysis or blood biochemistry, tests for renal function or histopathological examination of a range of tissues (Ito et al., 1979d).

(b) Hepatic toxicity

Dogs

In a study that did not comply with GLP, two male beagle dogs were given cefuroxime sodium in saline by subcutaneous injection at a dose of 0, 100 or 300 mg/kg bw per day for 10 days. One dog was given a single daily dose, while the other was given three divided doses, 8 h apart. There were no effects on body weight or general condition. Blood samples were taken 1, 4 and 8 h after injection on the first and eighth days and 24 h after the initial dose on the first, second and tenth days. The activities of alkaline phosphatase, alanine and aspartate aminotransferases, sorbitol dehydrogenase and glutamate dehydrogenase were not affected at any time. No histopathological changes were observed in the liver. As only a summary of this study was available, the findings cannot be confirmed independently (Glaxo Laboratories Ltd, 1986).

(c) Microbiological effects

Several studies were available on the effects of orally administered cefuroxime on the faecal bacterial flora of humans. These studies were carried out according to appropriate standards for study protocol and conduct.

Six healthy male volunteers aged 22–40 (weighing 70–86 kg) were given 10 oral doses of 60 mg of cefuroxime axetil, 8 h apart, for a total dose of about 8.5 mg/kg bw. Bowel function was recorded, and faecal samples were collected for microbio-logical analysis 2 days before and during treatment. Three of the six volunteers had diarrhoea during the dosing period which lasted for 2 days. Another had mild abdominal discomfort for 1 day. A decline in the number of Escherichia coli and coliforms (> 2 log) was seen in the faeces of the three men who developed diarrhoea. Similarly, there was a > 2 log-fold decrease in the number of Streptococcus faecalis in two men with diarrhoea. S. faecalis could not be detected in the third. The count of Candida spp. increased from 10³ to 10⁹ in two men with diarrhoea and to 10⁵ in the other. It had been shown previously that oral doses of cefuroxime and other cephalosporins can increase the proportion of yeast (Candida albicans) in the gastrointestinal flora (Thomakos et al., 1998). The number of Bacteroides spp. declined from 10¹⁰ to 10³ and those of Peptostreptococcus and Peptococcus spp. decreased from 10¹⁰ to < 10³ in two of the men with diarrhoea and to 5 × 10⁶ in the third. After cessation of dosing, the microbial counts returned to pre-treatment levels. There were no effects on Clostridium spp. (Wise et al., 1984).

Oral administration of cefuroxime axetil at a dose of 250 mg twice daily for 4.5 days to 10 healthy volunteers (five men, five women; mean age, 35 years) caused gastrointestinal disturbances. One of the subjects developed a feeling of nausea, and five reported a bloated feeling; seven reported soft faeces, and two detected a change in odour. Diarrhoea developed in four volunteers, and six reported an increased number of defaecations during a day. One woman developed vaginitis. Bowel function returned to normal within 5 days of completing treatment. Decreased total numbers of anaerobes and total aerobes were found in several individuals. The number of Enterobacteriaceae was reduced or even nil in six persons. Those of Streptococcus and Candida spp. were increased. Pseudomonas aeruginosa appeared in the faeces of four persons during the treatment period. Clostridium difficile and C. perfringens were not detected in any faecal samples, and no clostridial toxins were found. In three persons in whom Enterobacteriaceae were eliminated, recolonization with the sensitive species E. coli, Citrobacter freundii or Klebsiella ozaenae occurred. The populations of faecal flora returned to pre-treatment proportions about 7 days after cessation of treatment (Leigh et al., 1990).

Treatment of eight patients for acute exacerbation of bronchitis with cefuroxime axetil at a dose of 250 mg (~ 4.1 mg/kg bw) twice a day for 10 days resulted in reduced numbers of Staphylococci, Enterobacteriaceae and clostridial populations. These returned to pre-treatment levels 14 days after cessation of treatment. C. difficile appeared in three patients (Novelli et al., 1995). In another study, in which 15 recipients of liver transplants were given 6.3 g of cefuroxime (100 mg/kg bw), 0.6 g of tobramycin and 0.5 g of nystatin three times daily for 19–21 days to suppress the gut flora, only a few samples contained C. difficile. The diarrhoea induced by the treatment was self-limiting (Hove et al., 1996).

Minimum inhibitory concentrations (MICs) have been reported for a range of bacterial species.

Cefuroxime was included for comparison in a multicentre trial of agents against more than 42 000 gram-positive and gram-negative organisms. This survey from 79 medical centres and community hospitals in the USA made it possible to establish MIC₅₀ and MIC₉₀ values for Proteus mirabilis, P. vulgaris, Escherichia coli and Enterococcus faecalis (Murray et al., 1994). These data and data for the same organisms reported by Marshall, A. (1995) are shown in Table 3. The results are based on an inoculum density of 10⁷ CFU/ml. The two reports show closely similar values.

Numbers in parentheses are numbers of isolates studied.

MIC values for cefuroxime (sodium) against 100 bacterial strains, comprising 10 isolates of 10 genera derived from human gut isolates, were determined by an agar dilution method (Table 4). The bacteria tested are usually considered the most relevant and representative of human gut flora. Of the 10 groups tested, five genera (Enterococcus spp., Lactobacillus spp., Bifidobacterium spp., Peptostreptococcus spp. and Clostridium spp.) showed a strong inoculum effect (more than two antibiotic dilutions) between the undiluted culture and a 10^–2 dilution, and two genera (Bacteroides spp. and Bifidobacterium spp.) showed an inoculum effect between the 10^–2 and 10^–4 dilutions. The information available indicates that the lowest relevant MIC₅₀, at the highest inoculum level of 10⁹ CFU/ml, was 8 µg/ml for Bifidobacterium spp. (Marshall, R., 1995).

In a limited study of the susceptibility of 124 bacteria of aerobic origin isolated from patients with spontaneous bacterial peritonitis, the MIC₅₀ and MIC₉₀ values for E. coli were both 4 µg/ml, and the MIC₅₀ for Enterococcus spp. was > 16 µg/ml (Sader et al.,1995).

In a study specifically designed to determine the effects of inoculum size on MIC values, a clear inoculum effect was seen in several bacteria. Many cephalosporin antibiotics have an inoculum effect, which may be related to drug deactivation or metabolism (Goldstein et al., 1991). The significance of this observation is twofold. First, at high inocula, the activity of cefuroxime is greatly reduced; therefore, use of MICs for concentrations of organisms lower than those found in vivo in the gastrointestinal tract will result in overestimates of the potential of cefuroxime to affect the microflora adversely. Secondly, the data show potential beta-lactamase production, which in vivo would lead to inactivation of cefuroxime. This conclusion is supported by the work of Barry et al. (1977).

The effects of co-culture on the MIC and minimum bactericidal concentration of cefuroxime against 10 combinations of bacteria from the human gastrointestinal microflora were determined by agar dilution and by broth microdilution. The results (Table 5) showed that the activity of cefuroxime was significantly reduced, by a factor of up to 20, by co-culture as compared with monoculture. The relatively sensitive Fusobacterium mortiferum strain became less susceptible when tested in co-culture with a more resistant, beta-lactamase-producing Proteus vulgaris strain. This was not observed in all cases. The results also showed that the gut microrganisms can protect themselves against the antimicrobial effects of cefuroxime, thus affording protection of the overall gut ecosystem (Pridmore, 1996). Indeed, significant beta-lactamase activity has been detected in human faeces (Nord et al., 1989). Particular organisms are known to produce the enzyme, and some, like Bacteroides fragilis, have strains that produce high concentrations (Cornick et al., 1990). In a study of the beta-lactamase activity in bacteria used to determine the MICs of cefuroxime, 21 of the 100 strains representative of the human gut flora had intrinsic beta-lactamase activity, and a further eight isolates produced beta-lactamase in the presence of cefuroxime (Marshall, A., 1996).

MBC, minimum bactericidal concentration

Cefuroxime is unaffected by many of the common beta-lactamases and is effective against bacterial strains that are resistant to other beta-lactam antibiotics. Cefuroxime is stable to many bacterial beta-lactamases, especially plasmid-mediated enzymes that are commonly found in Enterobacteriaceae (Medical Economics Co., 2002).

A model was used to assess the effects of cefuroxime on bacteria representative of the human gut flora in vitro under conditions that mimicked those in the human gut. Two concentrations were used: one was based on the maximum concentration of cefuroxime residues expected to be found in the human gut, and the second was comparable to the MICs for cefuroxime against the respective human gut isolates. The effects of cefuroxime were investigated against five groups of bacteria (Clostridium sporogenes, Cl. difficile, Peptostreptococcus magnus, P. anaerobius, and Bacteroides spp.) found in the human gut. The drug was added to sterile anaerobic cooked-meat medium supplemented with pepsin and incubated anaerobically at pH 2 and 37 ^oC for 1 h. After adjustment to pH 7 and the addition of physiological levels of bile salts and pancreatin, the tester strain was added, and the culture was incubated anaerobically for 18 h. The results are given in Table 6.

    See Also:
       Toxicological Abbreviations
       Cefuroxime (WHO Food Additives Series 53)
       CEFUROXIME (JECFA Evaluation)