Nonclinical Toxicology Studies with Zidovudine: Reproductive Toxicity Studies in Rats and Rabbits

Zidovudine (ZDV) was evaluated for adverse effects on reproductionand fetal development in animal test species. Standard preclinicaltests for reproduction and fertility, developmental toxicity,and postnatal toxicity were conducted in CD (Sprague-Dawley)rats and a developmental toxicity study was conducted in NewZealand white rabbits. In an additional study, reproductiveoutcome was characterized in female rats given ZDV before, during,or after mating and drug levels in the plasma and milk of lactatingrats were determined. Finally, drug exposure data includingobserved peak plasma concentrations (C_max) and area under theconcentration-time curve (AUC) were evaluated for pregnant ratsand rabbits. In a reproduction/fertility study in CD rats, toxicityto the early rat embryo, manifested as an increase in earlyresorptions and a decrease in litter size, was noted followingdosage of the parental animals with 75 or 225 mg ZDV/kg bid.A dose of 25 mg/kg bid was a no-effect level in rats. At thetime of mating, male rats had been dosed for 85 days, and femaleshad been dosed for 26 days. To further evaluate the effectsof ZDV on reproduction, dosing of male rats was continued to149 days when they were mated a second time to virgin, untreatedfemales. All reproductive parameters were normal in the untreatedfemales from this second mating, indicating that the embryotoxiceffect of the drug was not likely mediated by a genotoxic orother effect in the male. A separate study in female CD ratsgiven 225 mg/kg bid for various periods pre- or postconceptionsuggests that the toxic effect of ZDV is primarily to the earlyrodent embryo. Early embryo death did not occur in rats or rabbitsin standard developmental (teratology) studies; however, pregnantNew Zealand white rabbits given 250 mg/kg bid during gestationDays 6–18 showed reduced weight gain, anemia, and an increasein late fetal deaths. No other evidence of developmental toxicitywas noted in either species, and ZDV was not teratogenic inrats or rabbits given up to 250 mg/kg bid during the periodof major organogenesis. At this dose, C_max, values in rats andrabbits were approximately 234 and 150 times higher, respectively,than the mean steady-state serum concentration in adults followingchronic oral administration of 250 mg every 4 hr. In both thereproduction/fertility study and a periand postnatal study inrats, liveborn offspring showed no adverse effects on survival,growth, or developmental measurements.     

Preclinical Toxicology Studies with Acyclovir: Carcinogenicity Bioassays and Chronic Toxicity Tests

Preclinical Toxicology Studies with Acyclovir: CarcinogenicityBioassays and Chronic Toxicity Tests. Tucker, W.E., Jr., Krasny,H.C., de Miranda, P., Goldenthal, E.I., Elion, G.B., Hajian,G. and Szczech, G.M. (1983). Fundam. Appl. Toxicol. 3:579–586.Acyclovir (ACV), a nucleoside analog that is a new herpes-specificantiviral drug, was given by gavage at 50, 150 and 450 mg/kg/dayto Sprague Dawley rats and Swiss mice for most of their lifetimeto assess chronic toxicity and carcinogenicity. Treatment withACV did not shorten the lifespan of either rats or mice. Infact, female mice given 150 and 450 mg/kg/day had significantlylonger mean durations of survival than control female mice whenanalyzed by the life table technique. There were no signs oftoxicosis produced by chronic exposure to ACV in either therats or mice, and there was no drug-related increase in neoplasmsin either species. Four groups of Beagle dogs were initiallygiven daily oral doses of 15, 45 or 150 mg/kg ACV in a 1 yearchronic toxicity study. Dogs treated at 150 mg/ kg/day vomited,had diarrhea, consumed less feed and lost weight within 2 weeks.Dogs treated at 45 mg/kg/day also had minimal signs of gastrointestinaltoxicosis. These dose levels were then decreased to 60 and 30mg/kg/day for the rest of the one year test period. With theexception of occasional and inconsistent emesis and diarrhea,the 60 mg/kg/day dose level was well tolerated. Some mid andhigh dose dogs had sore paws due to erosion of footpads andcracking, splitting and loosening of the nails first becomingevident during the 13th week of the study. Several of thesedogs subsequently lost the keratin from some claws. There wasnail regeneration and healing of footpads as the study progressed,with all claws appearing essentially normal at the end of 1year. Nails and footpads of dogs given 15 mg/kg/day were normalthroughout the study.     

Preclinical Toxicology Studies with Acyclovir: Genetic Toxicity Tests

Preclinical Toxicology Studies with Acyclovir: Genetic ToxicityTests. Clive, D., Turner, N.T., Hozier, J., Batson, A.G. andTucker, W.E., Jr. (1983). Fundam. Appl. Toxicol 3: 587–602.Acyclovir (ACV), an antiviral drug active in the treatment oforal and genital Herpes infections, has been evaluated for mutagenicand carcinogenic potential in a battery of in vitro and in vivoshort-termassays. Negative results were obtained in the following in vitrotests: Ames Salmonella, plate incorporation and preincubationmodification assays; E. coli polA⁺/polA^– DNA repair; yeast(S. cerevisiae D4) gene conversion; Chinese hamster ovary cells(HGPRT, APRT loci and ouabain-resistance marker); L5178 Y mouselymphoma cells (HGPRT locus and ouabain-resistance marker);and C3H/10Tmouse fibroblast neo-plastic transformation assay.All except the last assay were performed in the presence andabsence of an exogenous metabolic activation system. ACV waspositive at high concentrations x exposure times in the absenceof exogenous metabolic activation in the following in vitrosystems and at the indicated concentrations: BALB/c-3T3 neoplastictransformation (50 /µg/mL, 72 h exposure); human lymphocytecytogenetics (250–500 µg/mL, 48 h exposure); andL5178Y mouse lymphoma cells (TK locus, 400–2400 µg/mL,4 h exposure; predominantly small colony mutants of chromosomalorigin produced). No effects were seen in vivo (mouse dominantlethal assay; rat and Chinese hamster bone marrow cytogenetics)at up to maximum tolerated doses (MTD). An unusual clastogeniceffect was seen in Chinese hamsters at 5 times the MTD. Overall,positive effects were seen only at either high concentrations(250 µg/mL in vitro or plasma levels) or prolonged exposure(72 hr in the BALB/ c-3T3 neoplastic transformation assay).These studies support the view that ACV is a chromosomal mutagen,i.e., one which causes multi-locus damage but not single geneeffects. The significance of these results for the genetic riskof ACV to man is discussed.     

Nonclinical Toxicology Studies with Zidovudine: Acute, Subacute, and Chronic Toxicity in Rodents, Dogs, and Monkeys

In single dose acute toxicity studies in CD-1 mice and CD rats,the median lethal dose (MLD) for zidovudlne (ZDV) was >750mg/kg after iv dosing and >3000 mg/kg after po administration(recommended human dose is 100 mg every 4 hr while awake). Becauseof the short half-life in rats (0.8 hr), dogs (1.0 hr), andmonkeys (0.8 hr), the daily dose of ZDV in most studies wasgiven in two equal portions approximately 6 hr apart. Intravenousadministration of ZDV was well tolerated in beagle dogs at doselevels up to 42.5 mg/kg bid for 2 weeks and in CD rats at doselevels up to 75 mg/kg bid for 4 weeks. In a 2-week dose range-findingstudy in beagle dogs, cytostatic effects were noted at po doselevels of 62.5 to 250 mg/kg bid in certain tissues with rapidcell replication rates. In contrast, in 3-to 12-month oral toxicitystudies in CD rats and cynomolgus monkeys, the principal toxicologicfinding was reversible macrocytic normochromic anemia whichoccurred at 225–250 mg/kg bid in rats and 17.5–150mg/kg bid in monkeys. In the 12-month rat study, RBC was decreasedat 25 and 75 mg/kg bid. In the 12-month monkey study WBC wasslightly decreased at 150 mg/kg bid.     

Comparative Toxicity and Carcinogenicity Studies of Tetracycline and Oxytetracycline in Rats and Mice

Comparative Toxicity and Carcinogenicity Studies of Tetracyclineand Oxytetracycline in Ratsand Mice. DIETZ, D. D., ABDO, K.M., HASEMAN, J. K., EUSTIS, S. L., AND HUFF, J. E. (1991). FundarmAppl Toxicol. 17, 335–346. Two-year toxicity and carcinogenicitystudies of oxytetracycline hydrochloride and tetracycline hydrochloride,two structurally similar and widely used antibiotics, were performedin F344/N rats and B6C3F1 mice. Rats and mice were continuouslyexposed via their diet to the following levels of antibiotic:oxytetracycline HCl—rats 0, 25,000, or 50,000 ppm; mice0, 6,300, or 12,500 ppm; tetracycline HCI—rats and mice0, 12,500, or 25,000 ppm. On a milligram per kilogram of bodyweight basis these exposures represent doses that are 20 to140 times daily human therapeutic doses. Dose-related increasedsurvival was noted among oxytetracycline-treated male rats andtetracycline-treated female rats and male mice, while treatment-relatedreduced body weight gain occurred in oxytetracycline- and tetracycline-treatedmice. Microscopic changes Included fatty metamorphosis and focalcellular change in livers of oxytetracycline-treated male ratsand basophilic cytoplasmic and clear cell change in livers oftetracycline-treated male rats. The only neoplastic changeswere a marginally increased trend in phmchromocytoma of theadrenal medulla ( equivocal evidence only) among oxytetracyclineexposedmale rats (12/50 controls, 19/50 low dose, 24/50 high dose)and an increased incidence of pituitary adenoma or adenocarcinomaamong high-dose oxytetracycline-treated female rats (20/50 controls,32/50 high dose). Although oxytetracycline and tetracyclineappeared to increase the inadence of pituitary hyperplasia inhigh-dose male and female rats, respectively, the total incidenceof proliferative changes (hyperplasia, adenoma, and adenocarcinoma)was not affected by antibiotic exposure. The results from thesestudies therefore support the notion that neither antibioticis careinogenic in rodents. There were several negative trendssuggesting possible protective effats by both these tetracyclineanalogs against certain spontaneous neoplastic and nonneoplasticchanges.     

New Diet (NTP-2000) for Rats in the National Toxicology Program Toxicity and Carcinogenicity Studies

Composition of diet may influence growth, diseases, tumor rates,and responses to chemical treatment. Since 1980 the NIH–07open formula nonpurified diet has been the selected diet forthe National Toxicology Program (NTP) toxicity and carcinogenicitystudies in rodents. Studies with nonpurified experimental dietswith lower protein and higher fat and fiber than the NIH-07diet indicated that the diet for Fischer–344 (F344) ratsin long-term studies could be modified to decrease the severityof chronic diseases and to decrease/delay the development ofspontaneous tumors. Based on the results of these studies anew open formula nonpurified diet designated as NTP-2000 wasformulated to contain 14.5% protein, 8.5% fat, and 9.5% fiber.Corn, wheat, and wheat middlings contribute to about 60% ofthe ingredients; soybean meal, fish meal, and alfalfa meal arethe additional sources of protein; purified cellulose, oat hulls,and alfalfa meal are the major sources of fiber; and soy oiland corn oil are the major sources of fat in the NTP–2000diet. The Ca:P ratio and mineral and vitamin concentrationswere reformulated based on AIN–93 and NRC–95 recommendations.The NIH-07 and the NTP–2000 diets were fed to groups of6–week–old F344 rats for 13 weeks and evaluatedfor growth patterns, food and water consumptions, hematologyand clinical chemistry parameters, and organ weights and pathologicalchanges. Growth patterns and body weights were similar for bothdiets. Food consumptions were slightly higher and water consumptionswere slightly lower for the groups fed NTP–2000 diet.There were no differences in hematological parameters betweenthe groups fed the above diets. Serum levels of cholesterol,alkaline phosphatase, and 5' nucleotidase were slightly higherin groups fed the NTP–2000 diet possibly due to higherfat content of this diet. However, the serum triglyceride levelswere slightly lower in groups fed the NTP–2000 diet andit may be related to higher fiber content of the NTP–2000diet. The liver and kidney weights of the groups fed NTP-2000diet were significantly lower possibly due to lower proteincontent of this diet and lower protein consumption associatedchanges in Phase I and Phase II drug metabolizing enzyme systems.The adrenal weights were also lower in groups fed the new diet.The NTP–2000 diet prevented nephrocalcinosis and decreasedthe severity of nephropathy and cardiomyopathy, the common lesionsof F344 rats in 13–week studies. These results indicatethat the NTP–2000 diet is adequate for growth and maintenance of rats and appears to prevent or decrease the severityof diet-associated lesions.     

A Transplacental Carcinogenicity Bioassay in CD-1 Mice with Zidovudine

In oral carcinogenicity bioassays, zidovudine (ZDV) inducedvaginal epithelial cell tumors in mice given 30 or 40 mg/kg/dayand rats given 300 mg/kg/day. To determine if lifetime exposureto ZDV, beginning perinatally, would alter this pattern of carcinogenicity,two groups of 60 pregnant CD-I mice were given 20 or 40 mg/kg/dayof ZDV in 0.5% methyl cellulose from Gestation Day 10 throughLactation Day 21. At weaning, 2 pups per sex from each of 35litters in each group were assigned to the study and given 20or 40 mg/kg/day of ZDV in the drinking water until 17–35days of age, followed by daily gavage for 24 months. Two additionalgroups of 60 pregnant CD-I mice each were given 40 mg/kg/dayof ZDV daily from Gestation Day 10 through Lactation Day 21;in one, ZDV treatment was halted at weaning and in the other,treatment was stopped 90 days after weaning. Two other groupsof 60 pregnant CD-I mice were left untreated (environmentalcontrol) or were given 0.5% methyl cellulose beginning on GestationDay 10 (vehicle control). Vehicle control progeny received plaindrinking water for 17–35 days postweaning and then 0.5%methyl cellulose daily by gavage for 24 months. ZDV treatmentdid not affect survival or body weight in either sex. In femalesgiven 20 or 40 mg/kg/day of ZDV for 24 months there was mildmacrocytic anemia. Similar, non-dose-related changes were seenin males in these groups. ZDV-related tumor findings were limitedto the vagina, where there were 2 and 11 vaginal squamous cellcarcinomas in mice given 20 or 40 mg/kg/day of ZDV daily, respectively.This incidence was not remarkably different from that seen inpreviously reported bioassays. It was concluded that lifetimeoral treatment of mice with ZDV, beginning perinatally, didnot alter the previously reported pattern of carcinogenicityand that under the conditions tested ZDV was not a transplacentalcarcinogen.     

Inhalation Carcinogenicity and Chronic Toxicity of Carbon Tetrachloride in Rats and Mice

Carcinogenicity and chronic toxicity of carbon tetrachloride were examined by inhalation exposure of 50 F344 rats and 50 BDF1 mice of both sexes to carbon tetrachloride at 0 (clean air), 5, 25, or 125 ppm (v/v) for 6 h/day, 5 days/wk, for 104 wk. Incidences of hepatocellular adenomas and carcinomas in rats and mice of both sexes and of adrenal pheochromocytomas in mice of both sexes were significantly increased dose-dependently. Hepatocellular carcinomas and cirrhosis significantly occurred in the 125-ppm-exposed rats of both sexes, and 3 cases of hepatocellular carcinomas and increased incidences of hepatic altered cell foci were noted in the 25-ppm-exposed female rats. Hepatocellular carcinomas were induced in mice of both sexes at 25 and 125 ppm, and hepatocellular adenomas occurred in females at 5 ppm without any degenerative or necrotic change in hepatocytes. Hepatocellular carcinomas metastasized to the lung. The chronic hepatotoxicity was characterized by cirrhosis, fibrosis, and fatty change in rats, and ceroid deposition, bile-duct proliferation, and hydropic change in mice. Survival rates were decreased in the 125-ppm-exposed rats and mice of both sexes and in the 25-ppm-exposed female mice, in association with decreased body weights. The decreased survival rates were considered to be causally related to both various tumors including hepatocellular carcinomas and severe chronic progressive nephropathy in rats and to hepatocellular carcinomas in mice. This study provided clear evidence of carcinogenicity for carbon tetrachloride in rats and mice. A cytotoxic-proliferative and genotoxic mode of action for carbon tetrachloride-induced hepatocarcinogenesis was suggested.     

Studies on the Carcinogenicity of Pentachloroethane in Rats and Mice

Studies on the Carcinogenicity of Pentachloroethane in Ratsand Mice. Mennear, J.H., Haseman, J.K., Sullivan, D.J., Bernal,E. and Hildebrandt, P.K. (1982). Fundam. Appl. Toxicol. 2:82–87.The carcinogenicity of chronically administered (41 to 103 weeks)technical-grade pentachloroethane (PCE) was assessed in groupsof 50 male and female Fischer 344 rats and B6C3F₁ mice. Themajor contaminant in the PCE sample used for the chronic studywas hexachloroethane (4.2%). Prechronic studies (two and 13weeks repeated dose) employing gavage doses of from 5.0 to 1000mg/kg/day of PCE failed to reveal specific target organ toxicityin these species. In the absence of treatment-related pathologicalchanges during the prechronic tests, the doses for the chronicstudies were set on the basis of survival and body weight gainsduring the 13-week repeated dose study. During the chronic studiesdose levels of 75 and 150 mg/kg for rats and 250 and 500 mg/kgfor mice were administered, by gavage, five days per week. Thesurvival of high-dose rats (both sexes) was significantly reducedas compared to the survival of control animals and that of thelow-dose males was slightly, but not significantly, reduced.Although the administration of PCE to rats did not increasethe incidence of primary tumors, it did produce a significantdose-related increase in the incidence of chronic renal inflammationamong males. The survival times of all treated groups of micewere significantly shortened by PCE administration. Despitethis reduced survival time, the incidence of hepato-cellularcarcinoma was significantly increased in all treated groups.With the exception of a dose-related increase in the incidenceof hepatocellular adenoma among females, there were no othersignificant increases in primary tumor incidence in mice. Neitherrenal lesions in rats nor hepatocellular carcinoma in mice wereconsidered to be adequate explanations for the decreased survivals.Complete histopathological examinations failed to reveal thecause of decreased survival. The results of the study show thattechnical-grade PCE, like numerous other chlorinated ethanes,is an hepato-carcinogen for B6C3F₁ mice. This interpretationfor PCE per se, however, must be tempered because the majorcontaminant, hexachloroethane, has been shown to produce hepatocellularcarcinoma in mice. While the results obtained in rats suggesta species difference in susceptibility, the reduced survivalin this species may have contributed to the absence of a carcinogeniceffect.     

非临床毒性试验和致癌性试验动物死亡原因分析方法简介

本文简要介绍了美国国家毒理研究中心动物死亡原因分类、美国毒性病理学会颁布的判定毒性试验死亡原因的建议、英国亨廷顿生命科学公司病理部致癌性试验幼龄SD大鼠的死亡原因分析、美国华盛顿大学比较医学和比较病理学系啮齿类动物试验死亡原因分析推荐方法等内容,目的是为我国药物非临床安全性评价领域毒性病理学家更好地分析动物死亡原因及解释毒性试验和致癌性试验结果提供参考。     

Subchronic Oral Toxicity Studies with Erythritol in Mice and Rats

Erythritol is a sugar alcohol (polyol) with potential applications as a low-calorie, bulk sweetener. Ingested erythritol is efficiently absorbed and excreted unchanged via the urine since it is not metabolized systemically by the animal or human body. Erythritol was administered to four groups of 10 male and 10 female Swiss CD-1 mice and four groups of 15 male Wistar Crl:(WI) WU BR rats at dietary levels of 0, 5, 10, or 20% for 90 days. A fifth group of rats received a diet containing 20% erythritol on a time-restricted basis (6 hr/day), and a sixth group received a diet containing 20% mannitol for comparison. There were no treatment-related mortalities in either mice or rats. Soft stools and occasional diarrhea were observed in rats fed diets with 20% erythritol or mannitol but not in mice. Body weights were slightly yet significantly reduced in rats fed 20% erythritol or mannitol and in male mice of the 20% dose group. Erythritol intake in the high-dose group was approximately 12 g/kg body wt in rats and 44 and 45 g/kg body wt in male and female mice, respectively. Hematological and clinicochemical examinations of blood and plasma did not reveal any treatment-related effects. Urine output increased with increasing erythritol dose. In male and female mice of the 20% erythritol group, the creatinine-normalized urinary excretion of protein, K-glutamyltransferase (GGT), and electrolytes (Na⁺, K⁺, Ca²⁺, P_i, citrate) was significantly increased while urinaryN-acetylglucosaminidase (NAG) remained unchanged. At the 10% level, significantly increased urinary protein (both sexes) and GGT (males only) excretion were seen. In rats, the creatinine-normalized urinary excretion of GGT, NAG, and some electrolytes (Na⁺, K⁺, and Ca²⁺) was increased in some erythritol groups but a clear dose–response relationship was evident only for calcium. On termination of the study, cecal enlargement was seen in rats of the 10 and 20% dose groups and in mice of the 20% dose group. Increased relative and absolute kidney weights were observed in both sexes of mice in the 20% erythritol group, in male mice of the 5 and 10% groups, and in rats of the 10 and 20% erythritol groups. Histopathological examination did not reveal any treatment-related abnormalities in either mice or rats. In conclusion, the ingestion of erythritol for 90 days at dietary levels of up to 20% did not produce signs of toxicity in mice or rats. In particular, the morphological integrity of the kidneys was not adversely affected by the treatment in either species. The increases in urinary excretion of protein, GGT, NAG, and electrolytes were considered to result from extensive osmotic diuresis and a potential overload of the renal excretory system at the high dose levels employed.     

Chronic Toxicity and Carcinogenicity Study of Erythritol in Rats

The potential toxicity and carcinogenicity of erythritol, a low-calorie sugar substitute, were examined in Wistar Crl:(WI) WU BR rats. Groups of 50 rats of each sex consumed diets with 0, 2, 5, or 10% erythritol, or 10% mannitol, for a period of 104–107 weeks. To each of these main groups, two satellite groups of 20 males each were attached for interim kills after 52 and 78 weeks of treatment. At start of the study, the rats were 5–6 weeks old. The average intakes of erythritol in the 2, 5, and 10% groups were 0.9, 2.2, and 4.6 g/kg body wt/day for males and 1.0, 2.6, and 5.4 g/kg body wt/day for females, respectively. Mannitol intakes were 4.4 and 5.2 g/kg body wt/day in males and females, respectively. All treatments were well tolerated without diarrhea or other side effects. Body weights were significantly below control levels during most of the study in males of the 5% erythritol group and in males and females of the 10% erythritol and 10% mannitol groups. Survival of the animals was not adversely affected by the treatments. Hematological and clinicochemical examinations did not reveal noticeable changes which could be attributed to treatment. Analysis of urine samples collected during five 48-hr periods, from rats of the satellite groups in Weeks 26, 42, 50, and 78 and from rats of the main groups in Week 102, showed that about 60% of ingested erythritol was excreted unchanged. The urine volumes increased with increasing dietary erythritol levels. In line with previous observations on other polyols, erythritol and mannitol ingestion led to an increased excretion of urinary calcium and citrate. The urinary excretions of sodium, potassium, phosphate,N-acetylglucosaminidase (NAG), γ-glutamyltransferase (GGT), low-molecular-weight protein (LMP), and total protein (TP) were slightly elevated in the 10% erythritol group. Increased GGT and NAG excretions also were seen occasionally at the 5% dose. Significantly increased relative cecum weights were seen in rats of either sex in the 10% mannitol and, somewhat less pronounced, 10% erythritol groups. Some cecal enlargement also was seen in the 5% erythritol group. The relative weight of the kidneys was highest in the 10% erythritol group, the difference from controls reaching statistical significance at interim kills (males) and termination (females). Except for more frequent pelvic nephrocalcinosis in female rats of all erythritol dose groups, the histopathological examinations did not reveal any nonneoplastic, preneoplastic, or neoplastic changes that could be attributed to the ingestion of erythritol. In male and female rats of the 10% mannitol group, pelvic nephrocalcinosis, which in females was associated occasionally with pelvic hyperplasia, was the only remarkable finding. The incidence and progression of nephrosis, which is commonly seen in aging rats of this strain, were not influenced by the treatments. In the absence of morphological alterations in the kidneys or other signs of nephrotoxicity, the increased excretions of NAG, GGT, LMP, and TP are regarded as innocuous, functional sequelae of the renal elimination of erythritol. In conclusion, the toxicological profile of erythritol in rats resembles that of other polyols in several respects. Except for nephrocalcinosis, which is commonly seen in polyol-fed rats, no other treatment-related, morphological changes were observed in the kidneys. Evidence for a tumor-inducing or tumor-promoting effect of erythritol was not seen.     

Preclinical Toxicology Studies with Acyclovir: Acute and Subchronic Tests

Preclinical Toxicology Studies with Acyclovir: Acute and SubchronicTests. Tucker, W.E., Jr., Macklin, A.W., Szot, R.J., Johnston,R.E., Elion, G.B., de Miranda, P. and Szczech, G.M. (1983).Fundam. Appl. Toxicol. 3:573–578. Acyclovir (ACV), a newantiherpes drug, was evaluated for toxicity in a series of acuteand subchronic toxicity tests. Oral LD₅₀ values were greaterthan 10 000 mg/kg in male ICR mice and greater than 20 000 mg/kgin male Long Evans rats. When ACV was given iv, the LD₅₀ was405 mg/kg for male mice and greater than 600 mg/kg for malerats. Additionally, LD₅₀ values for male rats treated sc were1070, 790, 678, and 650 mg/kg in rats that were respectively,3, 10, 28 and 71 days old indicating that very young rats werenot more sensitive to acute toxic effects of ACV. There wereno signs of toxicosis in CD-1 mice given ACV by gavage at doselevels of 50, 150 and 450 mg/kg/day for 1 month. Obstructivenephropathy occurred in rats given 20, 40 and 80 mg/kg/day onceeach day by rapid iv injection for 3 weeks. Both 5 and 10 mg/kg/daywere no effect dose levels. Renal damage caused by precipitationof drug crystals in renal tubules and collecting ducts in ratsgiven ACV by rapid iv injection was readily reversible within2 weeks. Beagle dogs were given doses of 10, 20, 25, 50 and100 mg/kg b.i.d. by rapid iv injection for 1 month. All 8 dogsgiven 100 mg/kg b.i.d. died by the 8th day of treatment; 5 of8 dogs given 50 mg/kg b.i.d. died after 21 to 31 days of treatment.At 50 and 100 mg/kg b.i.d. the clinical signs of toxicosis werenumerous and mainly resulted from the underlying morphologicaland functional changes associated with hypoplasia of the esophagealand gastrointestinal mucosa, lymphoid tissue, and bone marrow.At the 20 and 25 mg/kg b.i.d. dose levels the kidney was thetarget organ; the principal indications of altered renal functionwere increased water intake and hyposthenuria. The dose levelof 10 mg/kg b.i.d. was a no effect level for Beagle dogs treatediv. Thus, in subchronic experiments, the rapid iv injectionof acyclovir caused precipitation of crystals in the renal tubules,resulting in obstructive nephropathy in rats and dogs. Primarytoxicity occurred only in the dog where high doses of acyclovircaused hypoplasia of certain tissues with rapid cell turnover.     

Subchronic Toxicity Studies of t-Butyl Alcohol in Rats and Mice

The purpose of this study was to evaluate the toxicity of t-butylalcohol, an important commodity chemical, an additive to unleadedgasoline, and a contaminant of drinking water. Ninety-day toxicitystudies were conducted in B6C3F1 mice and Fischer 344 (F344)rats of both sexes using dosed water. Dose levels of t-butylalcohol were 0, 0.25, 0.5, 1, 2, and 4% (w/v). Lethality wasobserved at the 4% level of both sexes and species. Weight-gaindepression was present in all dose levels of male rats; 4% femalerats; 1, 2, and 4% male mice; and 2 and 4% female mice. Waterconsumption was increased at lower dose levels in male ratsand decreased in the higher dose levels of both sexes of ratsand female mice. Clinical signs in rats were ataxia in bothsexes and hypoactivity in males. Clinical signs in mice wereataxia, abnormal posture, and hypoactivity. In rats, urine volumeswere reduced, in association with crystalluria. Gross lesionsat necropsy were urinary tract calculi, renal pelvic and ureteraldilatation, and thickening of the urinary bladder mucosa. Microscopiclesions were hyperplasia of transitional epithelia and inflammationof the urinary bladder. In male rats treated with t-butyl alcohol,microscopic renal changes were suggestive of -2/i-globulin nephropathy.No-effect levels for the urinary tract lesions were 1% in malerats and mice (803.7 mg/kg/day for the male rats and 1565.8mg/kg/day for the male mice) and 2% in female rats and mice(1451.5 mg/kg/day for the female rats and 4362.9 mg/kg/day forthe female mice). The results indicate that in rodents the urinarytract is the target organ for t-butyl alcohol toxicity, andmales are more sensitive to t-butyl alcohol toxicity than females.     

Carcinogenicity Studies of Oxazepam in Mice

Oxazepam is a benzodiazepine widely used as a sedative-hypnoticand antianxiety drug. In chronic studies, groups of 60 maleand 60 female Swiss-Webster (SW) or B6C3F₁ mice received oxazepamin feed at concentrations of 0, 2500, or 5000 ppm. Additionalgroups of 60 male and female B6C3F, mice received 125 ppm infeed to allow for study of mice with serum concentrations ofoxazepam similar to those achieved in humans taking a therapeuticdose. At 57 weeks, treatment-related mortality of exposed SWmice caused the study to be terminated. Enhanced systemic amyloidosiscontributing to heart failure was considered the principal causeof death. Hepatocellular adenomas and carcinomas were increasedin exposed SW mice. Survival of B6C3F₁ mice receiving 2500 and5000 ppm oxazepam was also lower than that of controls. Earlydeaths were due to increased incidences of hepatoblastoma andhepatocellular carcinoma, and nearly all mice receiving 2500or 5000 ppm developed hepatocellular neoplasia. An increasein follicular cell hyperplasia of the thyroid gland occurredin all exposed groups of B6C3F₁ mice, and thyroid gland follicularcell adenoma was increased in exposed females. Further studiesof the capacity of oxazepam to induce liver cell mitogenesisand an evaluation of the frequency of activated H- and K-rasoncogenes in the liver tumors of B6C3F₁ mice has shown thatmany of the neoplastic and nonneoplastic responses of mice tooxazepam resemble those observed with phenobarbital.     

Preclinical Toxicology Studies with Acyclovir: Ophthalmic and Cutaneous Tests

Preclinical Toxicology Studies with Acyclovir: Ophthalmic andCutaneous Tests. Tucker, W.E., Jr., Johnston, R.E., Macklin,A.W., Szot, R.J., Elion, G.B., de Miranda, P. and Szczech, G.M.(1983). Fundam. Appl. Toxicol. 3:569–572. Topical formulationsof acyclovir (ACV) were tested in animals to define potentialfor tissue irritation and systemic toxicity. Acyclovir ointments(5 and 10% concentrations in polyethylene glycol vehicle) producedno sign of dermal irritation or systemic toxicity when appliedto shaved abraded and intact skin of guinea pigs for 24 consecutivedays. Solutions (0.9% normal saline vehicle) of ACV did notsensitize guinea pigs when 10 sensitizing doses and a challengedose were injected intradermally. Petrolatum base ophthalmicointments containing 1 and 3% ACV did not produce significantocular irritation when applied to the corneas of New ZealandWhite rabbits 5 times each day for 21 consecutive days. A 6%petrolatum base ointment produced mild conjunctival irritationbut no sign of corneal or iridic toxicity. Mean concentrationsof 2.53 µM ACV were found in aqueous humor 2 hours aftera 1 cm ribbon (21 mg) of 3% ophthalmic ointment was placed inthe eyes of rabbits. A single treatment with a topical ointmentcontaining 5% ACV in polyethylene glycol vehicle produced minimalirritation when placed in the eyes of New Zealand White rabbits.     

Concordance between Rats and Mice in Bioassays for Carcinogenesis

According to current policy, chemicals are evaluated for possible cancer risk to humans at low dose by testing in bioassays in which high doses of the chemical are given to rodents. Thus, risk is extrapolated from high dose in rodents to low dose in humans. The accuracy of these extrapolations is generally unverifiable because data on humans are limited. However, it is feasible to examine the accuracy of extrapolations from mice to rats. If mice and rats are similar with respect to carcinogenesis, this provides some evidence in favor of interspecies extrapolations; conversely, if mice and rats are different, this casts doubt on the validity of extrapolations from mice to humans. One measure of interspecies agreement is concordance, the percentage of chemicals that are classified the same way as to carcinogenicity in mice and rats. Observed concordance in National Cancer Institute/National Toxicology Program bioassays is about 75%, which may seem on the low side because mice and rats are closely related species tested under the same experimental conditions. However, observed concordance could underestimate true concordance due to measurement error in the bioassays—a possibility demonstrated by Piegorschet al.(Risk Anal.12, 115–121, 1992). Expanding on this work, we show that the bias in observed concordance can be either positive or negative: an observed concordance of 75% can arise if the true concordance is anything between 20 and 100%. In particular, observed concordance can seriously overestimate true concordance.     

Chronic Toxicity Carcinogenicity Studies of Triethanolamine in B6C3F1 Mice

The chronic toxicity and carcinogenic potential of triethanolaminewas examined in B6C3F1 mice. Triethanolamine, dissolved in distilledwater at levels of 0 (control), 1, and 2%, was given to groupsof 50 males and 50 females ad libitum in drinking water for82 weeks. Neoplasms developed in all groups, including the controlgroup, but no dose-related increase of the incidence of anytumor was observed in treated groups of both sexes. There wereno adverse effects as regards survival of the mice, organ weights,and specific incidence of neoplasms in the treated, comparedto the control group. This chronic toxicity test provides noevidence of carcinogenic potential of triethanolamine in B6C3F1mice.     

Studies on the Short-Term Toxicity of Theophylline in Rats and Mice

Studies on the Short-Term Toxicity of Theophylline in Rats andMice. LINDAMOOD, C, III, LAMB, J. C, IV, BRISTOL, D. W., COLLINS,J. J., HEATH, J. E., AND PREJEAN, J. D. (1988). Fundam. Appl.Toxicol 10, 477–489. The purpose of these studies wasto evaluate the short-term toxicity of theophylline, a compoundpresent in tea and used in a variety of clinical applications.Fourteen-day repeated-dose toxicity studies were conducted inB6C3F1 mice and F344 rats of both sexes. Theophylline was administeredin feed (0, 500, 1000, 2000, 4000, and 8000 ppm) or by gavagein corn oil (12.5-twice daily, 25, 50, 50-twice daily, 100,200,200-twice daily, and 400 mg/kg). Dosed-feed exposure to theophyllineat concentrations up to 8000 ppm induced no significant toxicityexcept for dose-related uterine hypoplasia in rats. Palatabilityproblems at that level precluded administration of higher concentrations.In the gavage study, 400 mg/kg was acutely toxic for both species,but mice and rats differed in that this same daily dose administeredas two separate doses of 200 mg/kg was acutely toxic in ratsbut not in mice. No dose-related weight gain depression wasevident in mice; weight gain was depressed in the majority ofdose levels in rats and was pronounced at the higher levels.Clinical signs in mice were squinting and distended testes inmales, and in rats, rapid respiration (all doses), squinting,and hunching. Gross necropsies, organ weights, clinical pathology,and pathology identified no target organs in mice, while histopathologicobservations in rats suggested heart and stomach as possibletarget organs. Histopathologic effects in a number of othertissues, including lung, thymus, bone marrow, spleen, and uterus,were considered to reflect agonal changes in treated rats, possiblyrelated to inanition. The results suggest that both speciesand sex differences exist with respect to sensitivity to theophyllinetoxicity, with F344 rats being more sensitive than B6C3F1 miceand male rats being more sensitive than female rats.     

Toxicity and Carcinogenicity Studies of Nalidixic Acid in Rodents

ABSTRACT

Toxicity and carcinogenicity studies of nalidixic acid, an antimicrobial agent used to treat bacterial infections of the urinary tract, were conducted in F344/N rats and B6C3F mice of each sex for 13 weeks or 2 years. In the 13–week studies, nalidixlc acid was administered at dietary concentrations ranging from 1,000 to 16,000 pp. Body weights of both rats and mice were reduced in the groups receiving diet containing 8,000 and 16,000 ppm, and feed consumption of rats in the highest treatment groups was approximately tw-thirds that of controls. Degeneration of the germinal epithelium in the seminiferous tubules of the testis was observed in male rats that received 16,000 ppm; no other compound-related histopathologic effects were observed in either species. TWo-year studies were conducted by feeding diets containing 0, 2,000, or 4,000 ppm nalidixic acid to groups of 50 rats and mice/sex/group. The average daily feed consumption was slightly reduced compared to control groups and resulted in approximate daily doses of 82 or 175 mg nalidixic acidfig for low dose and high dose rats, and 220 or 475 mg/kg for low dose and high dose mice. Mean body weights of dosed rats and mice were lower than those of controls, except for groups of low dose female rats and male mice. The incidences of preputial gland neoplasms in dosed male rats and of clitoral gland neoplasms in dosed female rats were significantly increased compared to those in controls; responses in low dose groups were similar to those in high dose groups. There were decreased incidences of leukemia and mammary gland neoplasms in dosed female rats and of pituitary gland neoplasms in dosed male rats. Subcutaneous tissue fibrosarcomas were marginally increased in dosed male mice. There were no increased incidences of neoplasms in dosed female mice. under the conditions of these studies, the dietary administration of nalidixic acid was carcinogenic for rats, causing preputial gland or clitoral gland neoplasms in males and females, respectively. The association of subcutaneous neoplasms with administration of nalidixic acid to male mice was equivocal.