BITERTANOL
EXPLANATION
Bitertanol was first evaluated by the 1983 JMPR which allocated a
temporary acceptable daily intake of 0-0.005 mg/kg bw and required, by
1987, metabolism studies to clarify the metabolic pathway of
bitertanol in mammals, an oral toxicity study in the dog with minimum
duration of one year and a chronic toxicity and carcinogenicity study
in rats at appropriate dosage (Annex 1, WHO/FAO, 1984). Relevant data
has been submitted for evaluation by the present Joint Meeting and is
summarized in this monograph addendum.
EVALUATION FOR ACCEPTABLE INTAKE
BIOLOGICAL DATA
Biochemical Aspects
Absorption, Distribution and Excretion
Groups of 5 male and 5 female Wistar rats received either a
single oral dose of 14C-phenyl-radiolabelled bitertanol solution in
ethylene glycol (100 mg/kg or 100 mg/kg), a single intravenous dose
(100 mg/kg) or 14 daily oral doses (100 mg/kg) Followed by a single
oral dose of 14C-radiolabelled bitertanol (100 mg/kg). Urine and
fetes were collected 6 and 24 hours after dosing and subsequently at
24 hour intervals until sacrifice, 7 days later. Serial blood samples
were collected during this period.
Faecal excretion of radioactivity following intravenous
administration indicates that biliary excretion was predominant. In
each case 14C-radioactivity was mostly excreted in the faeces.
Urinary excretion amounted to about 4-11% of administered dose whilst
expired radioactivity was not detectable. Total recoveries of
radioactivity were high, about 92-104%.
Pharmacokinetic analysis indicated that absorption of an oral
dose of bitertanol followed a first order pattern at the single and
repeated low dose (100 mg/kg) but not at the higher dose (1000 mg/kg),
suggesting saturation of absorption, distribution or elimination
processes. The highest tissue levels detected were in liver (17.9 ppm,
female) and kidney (5.9 ppm, male) of the high-dose groups. Tissue
residues totalled about 0.2-0.4% of administered radioactivity (Puhl &
Hurley, 1983).
Metabolism
Alternative pathways for the metabolism of absorbed bitertanol is
shown in the Figure. Hydroxylation of the para-position of the
biphenyl and of a methyl group of the sec-butyl moieties gave rise to
phenolic (1) and diol (2) metabolites. Although one diastereomer of
the latter was detectable, it underwent oxidation to the corresponding
butanoic acid (4) and subsequent ring hydroxylation (5). The
para-hydroxylated diol (6) was also detected as was
4,4-dihydroxybiophenyl (7). Other hydroxylated metabolites (8,9,10)
were also tentatively identified (Puhl & Hurley, 1983).
Toxicological Studies
Special Study on Hepatotoxicity
Groups of 10 male and 10 female Wistar rats received by gavage 0,
30, 100 and 300 mg/kg bitertanol (95.8% purity) suspended in distilled
water with Cremorph EL daily for 14 days. On sacrifice, blood was
collected for detailed hematological and clinical chemistry
examination and liver samples taken for detailed histopathology and
enzyme studies.
During treatment female rats of the mid- (1/10) and high-dose
(9/10) groups exhibited hair loss. In some cases, weight loss occurred
in mid- and high-dose rats while low-dose females had reduced
bodyweight gain in comparison with control animals.
Female rats had a dose-related tendency to mild thrombocytosis
which was significant at mid- and high-doses only. Serum
gamma-glutamyl transpeptidase and bilirubin levels were slightly
raised in high dose female rats.
There were no gross pathological findings at necropsy. Liver
weights tended to be increased at mid- and high-doses, especially in
females. Histopathology showed slight to moderate bile duct
proliferation with peribiliary infiltration of monocytes or
polynucleocytes at mid- and high-doses. Sometimes these changes were
accompanied by the presence of parenchymal Councilman bodies or, more
occasionally, mitoses. The high-dose hepatocytes were occasionally
swollen with finely granular cytoplasm. Fatty infiltration was not
remarkable.
Results of the in vitro studies were consistent with induction
of hepatic microsomal enzymes: cytochrome P-450 content increased in a
dose-related manner, especially in males. Aminopyrene N-demethylase
activity was increased in high-dose males and females and in mid-dose
males while O-demethylase activity was increased in mid-and high-dose
males and high-dose female rats. Hepatic triglyceride content was not
influenced by bitertanol treatment.
The results of this study indicate that bitertanol caused mild
hepatotoxicity with modest induction of hepatic microspinal activity
in rats at 100 and 300 mg/kg (Mihail & Luckhaus, 1985).
Short-term Studies
Dogs
Groups of 4 male and 4 female beagle dogs received bitertanol
(95-97.3% purity) for two years in the diet at 0, 10, 40 or 160 ppm.
Although the control dogs exhibited a greater increase in bodyweight
than did treated dogs, no relationship with bitertanol treatment was
observed. Good nutritional status was maintained by dogs of all groups
and there were no significant differences between groups in food and
water consumption. No abnormalities were seen on examination or
selected reflexes, body temperature and pulse rate. However, 3 of 8
high-dose dogs developed bilateral cataracts. Urinalysis and
hematological examination, conducted at approximately 3 month
intervals, revealed no abnormalities. However, serum alanine
amino-transferase and alkaline phosphatase were elevated at 40 and
160 ppm.
At necropsy, the mean liver weight of high-dose dogs only were
markedly increased. Histological examination showed mild to moderate
vacuolation of adrenal zona reticularis epithelia at and above 40 ppm.
Based on this finding, the no observed effect level indicated by this
study is 10 ppm in the diet (Hoffman & Groening, 1983).
In another study, groups of 6 male and 6 female beagle dogs were
fed 0, 3 and 25 ppm bitertanol (96.3-96.7%) in the diet for 12 months.
A high dose group was maintained on a diet containing 200 ppm
bitertanol for 20 months to permit continued ophthalmoscopic
examination.
Treatment had no apparent effect on the dogs' behaviour,
appearance or nutritional status. Food consumption and bodyweight gain
were also unaffected. Physical examinations of pulse rates, body
temperature and selected reflexes were unremarkable. Ophthalmoscopy,
conducted at 3 monthly intervals in the control, low- and mid-dose
groups was normal. However, in the high-dose group, one dog developed
severe bilateral lenticular cataracts, observable from week 58. Four
other animals exhibited slight lens opacification by week 85. In
addition, dogs of this group also had signs of conjunctivitis with
nasociliary discharge and incrustation. Intermittent elevation of
serum hepatic alanine amino-transferase, glutamate dehydrogenase and
alkaline phosphatase also occurred in the high-dose dogs. Other usual
clinical chemical, hematological and urinalysis parameters were not
affected by treatment in any group.
At necropsy there was no grossly abnormal pathology. The adrenal
weights of high-dose dogs were apparently increased in comparison to
controls and lipoid vacuolations were observed in zona reticularis
epithelia. The results of this study accord with the previous findings
(Hoffman & Vogel, 1983).
Rabbits
In a repeated-dose study, bitertanol (95.8% pure) in a aqueous
suspension (0.5 ml) was applied to the intact or abraded dorsal and
lateral skin of groups of 6 male and 6 female New Zealand rabbits 6
hours daily 5 times per week for 3 weeks at 0, 50 and 250 mg/kg. The
animals were inspected for signs of dermal irritation 24 hours after
each treatment. Hematological, clinical chemical and urinalysis
parameters were investigated at termination and the animals necropsied
for further examination.
Dermal exposure to bitertanol had no apparent effect on
appearance or behaviour, bodyweight or survival of the rabbits.
Transient erythema developed for a few days at the exposure areas,
initially with abraded skin but later with intact skin. There was no
effect on skin-fold thickness, hematology, clinical chemistry or
urinalysis parameters. At necropsy, there were no gross pathological
findings. Histopathological examination showed a slight epidermal
thickening in exposed areas only of all treated animals. This study
indicates that bitertanol is a weak skin irritant only.
In vitro liver preparations showed no evidence of induction of
microsomal N-demethylation or O-demethylation or Cytochrome P-450
content (Heimann & Vogel, 1984).
COMMENTS
The 1983 JMPR requested data to clarify the metabolic pathway of
bitertanol and additional toxicological data from a one year dog study
and chronic and carcinogenicity studies in rats.
In rats, bitertanol is extensively metabolized, primarily by ring
and side chain hydroxylation, oxidation to the corresponding
carboxylic acid and also by ether cleavage. Pharmacokinetic studies
demonstrate that it is absorbed more completely at lower (100 mg/kg
bw) than at higher (1000 mg/kg bw) doses. Tissue retention of absorbed
material is low and biliary excretion predominates.
Data evaluated by the 1983 JMPR show that short-term feeding of
bitertanol to rats produced body weight depression and hepatotoxicity
at 600 and 2400 ppm, (equivalent top 60-240 mg/kg bw/day). Body weight
depression was seen in a 90-day study at 300 ppm (30 mg/kg bw/day). On
chronic administration, bitertanol retarded the growth of rats at
500 ppm (25-50 mg/kg bw/day).
In view of the reduced absorption of bitertanol at high doses
that has now been demonstrated, and because of the above mentioned
toxicity to rats at relevant doses, the meeting considered that
further chronic or carcinogenicity studies in rats would be unlikely
to yield new information of toxicological significance.
An additional study confirms that dogs are more susceptible to
bitertanol than rats. Feeding studies of one and two years' duration
show the formation of cataracts, conjunctivitis and mild
hepatotoxicity, with a no-observed-adverse-effect level at 10 ppm.
TOXICOLOGICAL EVALUATION
LEVELS CAUSING NO TOXICOLOGICAL EFFECT
Rat: 20 ppm in the diet, equivalent to 1 mg/kg bw/day.
Dog: 10 ppm in the diet, equivalent to 0.25 mg/kg bw/day.
ESTIMATE OF ACCEPTABLE DAILY INTAKE FOR MAN
0-0.003 mg/kg bw.
STUDIES WHICH WILL PROVIDE INFORMATION VALUABLE IN THE CONTINUED
EVALUATION OF THE COMPOUND
Observations in man.
REFERENCES
Heimann, K.G. & Vogel, O., 1984. KWG 0599 Subacute Study of Dermal
Toxicity to Rabbits. Unpublished study from Bayer AG Institute of
Toxicology Report No. 12571. Submitted to WHO by Bayer AG, Leverkusen,
FRG.
Hoffman, K. & Groening, P., 1983. KWG 0599/Chronic Toxicity Study on
Dogs (2-Year Feeding Experiment). Unpublished study from Bayer AG
Institute of Toxicology Report No. 12307. Submitted to WHO by Bayer
AG, Leverkusen, FRG.
Hoffman, K. & Vogel, O., 1983. KWG 0599 (Bitertanol)/Second Chronic
Toxicity Study with Dogs on Oral Administration. Unpublished study
from Bayer AG Institute of Toxicology Report No. 12328. Submitted to
WHO by Bayer AG, Leverkusen, FRG.
Mihail, F. & Luckhaus, G., 1985. KWG 0599 (Bitertanol)/Subacute Oral
Toxicity Study with Special Attention to Effect on the Liver.
Unpublished study from Bayer AG Institute of Toxicology Report
No. 13230. Submitted to WHO by Bayer AG, Leverkusen, FRG.
Puhl, R.J. & Hurley, J.B., 1983. The Absorption, Excretion and
Metabolism of Baycor TM-phenyI-UL-C14 by Rats. Unpublished study from
Mobay Chemical Corporation Agri. Chem. Division. Report No. 85832.
Submitted to WHO by Bayer AG, Leverkusen, FRG.
See Also:
Toxicological Abbreviations
Bitertanol (Pesticide residues in food: 1983 evaluations)
Bitertanol (Pesticide residues in food: 1984 evaluations)
Bitertanol (JMPR Evaluations 1998 Part II Toxicological)