Investigational New Drug‐Directed, 5‐Day Repeat Dose Toxicity Study of 4‐[3‐(2‐Nitro‐1‐Imidazolyl)‐Propylamino]‐7‐Chloroquinoline Hydrochloride (NLCQ‐1, NSC 709257) Administered with or without Taxol® in Sprague–Dawley Rats

Abstract: In pre‐clinical studies, 4‐[3‐(2‐nitro‐1‐imidazolyl)‐propylamino]‐7‐chloroquinoline hydrochloride (NLCQ‐1, NSC 709257) is a weak DNA‐intercalating, hypoxia‐selective cytotoxin with a promising profile as an adjuvant to radio/chemotherapy and it is about to enter phase I clinical trials. The present investigation was undertaken to further evaluate potential systemic toxicity induced by i.v. doses of NLCQ‐1 alone or in combination with Taxol ^® in Sprague–Dawley rats, in support of an investigational new drug application. Doses of NLCQ‐1 were based on previous range‐finding studies. In the present study, NLCQ‐1 was administered either alone, at 0, 6, 9 or 12 mg/kg/dose to male rats and 8, 12 or 16 mg/kg/dose to female rats or, at 9 (male rats) and 12 (female rats) mg/kg/dose, in combination with Taxol^®, on a qd × 5 schedule. Taxol^® was administered i.v. at 3.5 mg/kg/dose 1 hr before NLCQ‐1. Observations were recorded for mortality/moribundity, clinical signs of toxicity, body weights, food consumption, haematology, clinical chemistry, gross lesions at necropsy and histopathology. Blood samples were taken from 10 animals from each dose group on each of 2 days (days 8 and prior to scheduled necropsy on day 33). Administration of i.v. doses of NLCQ‐1 alone, on a qdx5 schedule, resulted in no signs of toxicity over the 33‐day study. Taxol^®‐induced toxicity included minimal decreases in the group mean RBC, haemoglobin and haematocrit values, minimal increases in group mean reticulocyte counts (females), marked decreases in group mean neutrophil counts and minimal decreases in group mean monocyte and eosinophil counts. Lymphoid atrophy of thymus, atrophy of bone marrow and atrophy of the germinal epithelium of the testis were also associated with the administration of Taxol^®. There was no additional toxicity associated with the co‐administration of NLCQ‐1 and Taxol^®. In the present study, the ‘no observable adverse effect level’ for NLCQ‐1, when administered on a qdx5 schedule, was >12 and >16 mg/kg/dose in male and female rats respectively. Daily administration of 9 (male rats) or 12 (female rats) mg/kg of NLCQ‐1 1 hr after i.v. administration of Taxol^® (3.5 mg/kg) had no effect on Taxol^®‐induced toxicity.     

A Subchronic Intravenous Toxicity Study of Magnesium Fructose‐1,6‐Diphosphate in Beagle Dogs

Abstract: Magnesium fructose‐1,6‐diphosphate is a novel agent of antimyocardial ischaemia. In the present study, the subchronic toxicity of magnesium fructose‐1,6‐diphosphate was investigated after 13‐week repeated intravenous administration in beagle dogs. The animals received doses of 0, 75, 150 and 300 mg/kg/day (three males and three females for each dose). During the study period, clinical signs, mortality, body weights, food consumption, electrocardiogram, urinalysis, haematology, clinical biochemistry, macroscopic findings, organ weights and histopathology were examined. The administration of magnesium fructose‐1,6‐diphosphate resulted in increased incidence of clinical signs, including salivation and emesis. These effects were transient and were noted in almost all dogs given 300 mg/kg/day and occasionally noted in the 150 mg/kg/day dose‐treated animals. Serum magnesium in the 150 mg/kg/day and 300 mg/kg/day dose‐treated animals was significantly increased after 6‐ and 13‐week administration, but recovered at the end of a 2‐week recovery period. At 6 weeks, a statistically significant decrease in serum electrolytes, including sodium and potassium, was observed in the treatment groups. There were no other treatment‐related findings. Under the conditions of the present study, magnesium fructose‐1,6‐diphosphate did not show any evidence of target organ toxicity. The no‐observed‐adverse‐effect level for 13‐week intravenous administration of magnesium fructose‐1,6‐diphosphate to beagle dogs was considered 75 mg/kg/day based on observations of clinical signs and serum electrolytes.     

Pre-clinical toxicity studies on the new nitroimidazole 1-methylsulphonyl-3-(1-methyl-5-nitroimidazole-2-yl)-2- imidazolidinone

Administration of 1-methylsulphonyl-3-(1-methyl-5-nitro-2-imidazole-yl)-2-imidazolidinone (Go 10213) at a dose of 5000 mg/kg to rat, mouse, guinea pig and rabbit and 3000 mg/kg to dog did not induce any toxic symptoms or mortality. Repeated daily gavaging with doses ranging from 50-3000 mg/kg/day were tolerated by rats for 2 weeks. No mortality was noticed in treated animals. Reduction in weight gain was observed in male rats on 2000 mg/kg per day and females on 1000 mg/kg per day. No toxic changes were noticed in dogs treated with 200 mg/kg per day for 2 weeks. One monkey treated with 75 mg/kg per day for 4 weeks tolerated the compound without exhibiting any toxic effects. No drug induced alterations were noticed in rats gavaged with 60 and 200 mg/kg per day for 4 weeks. Rats treated with a daily dose of 600 mg/kg showed reduction in body weight gain and atrophy of testes and these changes were reversible after stopping of medication. Dogs medicated with 30 and 100 mg/kg per day tolerated the drug for 4 weeks. Except slight ataxia in a few dogs treated with 100 mg/kg per day, no other drug induced toxic effects were noticed. Neurological symptoms were noticed in all dogs on high dose of 200 mg/kg. Three animals out of six were sacrificed in extremis in this dose. After discontinuation of Go 10213 all dogs on 100 and 200 mg/kg per day recovered normal gait in about a week. No definitive drug induced changes were noticed in laboratory investigations, gross and histopathological examinations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Single dose oral toxicity study of BMY-28100 in juvenile rats and dogs

In order to investigate the single dose oral toxicity of BMY-28100 in juvenile animals, the drug was administered in single doses to 4-day-old and 14-day-old Crj: CD (SD) rats of both sexes at a dose of 2,000 mg/kg, and to 4-week-old beagle dogs of both sexes at doses of 500, 1,000 and 2,000 mg/kg by oral route. The results obtained are summarized as follows: 1. In rats, decreases of the body weight gain were observed for male and female rats treated with the drug on postnatal day 4 through 5 days and 3 days after dosing, respectively. There were no apparent drug-related toxic signs. No deaths occurred during the observation period. Enlargement of the cecum was found in a few rats of both sexes administered the drug on postnatal day 4 or 14. 2. In dogs, watery-mucous diarrhea observed at 2 to 3 hours after dosing in all dose groups was not dose-related. This finding lasted in some dogs till 4 days after dosing. An increased incidence of emesis was induced in all males at 2,000 mg/kg and all females of all dose groups except one female at 2,000 mg/kg. Body weights increased normally for all dogs, but one male at 1,000 mg/kg showed a transient decrease in food consumption. No drug-related histopathological changes were found. Based upon these results, BMY-28100 at 2,000 mg/kg induced no apparent toxic changes in the present experimental conditions. Therefore, the single dose oral toxicity of the drug in juvenile animals appeared to be very slight and generally similar to that in adults.(ABSTRACT TRUNCATED AT 250 WORDS)     

Toxicity study of cefmatilen hydrochloride hydrate (S-1090) (2)--Single oral dose toxicity study in dogs

Cefmatilen hydrochloride hydrate (S-1090) was administered at 500 and 1000 mg potency/kg once orally to beagle dogs. No deaths occurred. Vomiting, diarrhea or mucous feces occurred on the dosing day, and reddish-brown feces (due to chelated products of S-1090 and its decomposition products with Fe3+ in the diet) were also observed on the dosing and next day. Increases of plasma urea nitrogen and iron were observed on the next day after dosing. No remarkable changes were noted in other examination items. The animals in both groups were considered to be exposed to a similar level of S-1090 based on the toxicokinetic data. The oral lethal dose of S-1090 in dogs was estimated to be more than 1000 mg potency/kg.     

Melatonin Protects Against Mercury(II)‐Induced Oxidative Tissue Damage in Rats

Abstract: Mercury exerts a variety of toxic effects in the body. Lipid peroxidation, DNA damage and depletion of reduced glutathione by Hg(II) suggest an oxidative stress‐like mechanism for Hg(II) toxicity. Melatonin, the main secretory product of the pineal gland, was recently found to be a potent free radical scavenger and antioxidant. N‐Acetylcysteine, a precursor of reduced glutathione and an antioxidant, is used in the therapy of acute heavy metal poisoning. In this study the protective effects of melatonin in comparison to that of N‐acetylcysteine against Hg‐induced oxidative damage in the kidney, liver, lung and brain tissues were investigated. Wistar albino rats of either sex (200–250 g) were divided into six groups, each consisting of 8 animals. Rats were intraperitoneally injected with 1) 0.9% NaCl, control (C) group; 2) a single dose of 5 mg/kg mercuric chloride (HgCl₂), Hg group; 3) melatonin in a dose of 10 mg/kg, 1 hr after HgCl₂ injection, Hg‐melatonin group; 4) melatonin in a dose of 10 mg/kg one day before and 1 hr after HgCl₂ injection, melatonin‐Hg‐melatonin group; 5) N‐acetylcysteine in a dose of 150 mg/kg, 1 hr after HgCl₂ injection, Hg‐N‐acetylcysteine group, and 6) N‐acetylcysteine in a dose of 150 mg/kg one day before and 1 hr after HgCl₂ injection, N‐acetylcysteine‐Hg‐N‐acetylcysteine group. Animals were killed by decapitation 24 hr after the injection of HgCl₂. Tissue samples were taken for determination of malondialdehyde, an end‐product of lipid peroxidation; glutathione (GSH), a key antioxidant, and myeloperoxidase activity, an index of neutrophil infiltration. The results revealed that HgCl₂ induced oxidative tissue damage, as evidenced by increases in malondialdehyde levels. Myeloperoxidase activity was also increased, and GSH levels were decreased in the liver, kidney and the lungs. All of these effects were reversed by melatonin or N‐acetylcysteine treatment. Since melatonin or N‐acetylcysteine administration reversed these responses, it seems likely that melatonin or N‐acetylcysteine can protect all these tissues against HgCl₂‐induced oxidative damage.     

Toxicological safety evaluation of the human‐identical milk oligosaccharide 6′‐sialyllactose sodium salt

Human milk oligosaccharides (HMOs) are abundant in breastmilk, but their presence in infant formula is negligible. Sialylated HMOs, such as 6′‐sialyllactose, constitute a significant portion of the HMO fraction of human milk and are linked to important biological functions. To produce infant formula that is more comparable with human milk, biosynthesized sialyllactoses known as human‐identical milk oligosaccharides (structurally identical counterparts to their respective naturally occurring HMOs in breastmilk) are proposed for use in infant formula and other functional foods for the general population. To support the safety of 6′‐sialyllactose sodium salt (6′‐SL), a 90‐day oral (gavage) toxicity study and in vitro genotoxicity tests were conducted. The 90‐day study is the first to be conducted with 6′‐SL using neonatal rats (day 7 of age at the start of dosing), thus addressing safety of 6′‐SL for consumption by the most sensitive age group (infants). In the 90‐day study, neonatal rats received 6′‐SL at doses up to 5000 mg/kg body weight (BW)/day and reference controls received 5000 mg/kg BW/day of fructooligosaccharide (an ingredient approved for use in infant formula) for comparison with the high‐dose 6′‐SL group, followed by a 4‐week recovery period. There was no evidence of genotoxicity in vitro. No test item‐related adverse effects were observed on any parameter in the 90‐day study, thus the high dose (5000 mg/kg BW/day) was established as the no‐observed‐adverse‐effect level. These results confirm that 6′‐SL is safe for use in formula milk for infants and in other functional foods for the general population.     

Increased Plasma Endothelin‐1 and Cardiac Nitric Oxide during Doxorubicin‐Induced Cardiomyopathy

Abstract: The major limiting factor in long‐term administration of doxorubicin is the development of cumulative dose‐dependent cardiomyopathy and congestive heart failure. Although several mechanisms have been suggested to explain the exact cause of doxorubicin‐induced cardiomyopathy, the role of the vascular endothelium‐derived vasoactive mediators in the pathophysiology of this toxic effect is still unknown. Accordingly, the present study has been initiated to investigate whether the changes in plasma level of endothelin‐1 and nitric oxide along with cardiac nitric oxide are associated with the development of doxorubicin‐induced cardiomyopathy. Doxorubicin was injected with a single dose of 5 mg/kg and every other day with a dose of 5 mg/kg, intraperitoneally, to have four cumulative doses of, 10, 15, 20 and 25 mg/kg in five separate groups of male rats. An additional group receiving a single dose of 20 mg/kg and one receiving normal saline were also included in the study. Twenty‐four hr after the last dose, the animals were sacrificed and the plasma levels of endothelin‐1 and nitric oxide in addition to cardiac nitric oxide were determined. The results show that doxorubicin caused a statistically significant increase of 85%, 76% and 97% in plasma endothelin‐1 at a cumulative dose levels of 10, 15 and 20 mg/kg, respectively. However, the level of plasma nitric oxide remained unchanged. Furthermore, doxorubicin treatment resulted in a significant dose‐dependent increase in serum lactate dehydrogenase and creatine phosphokinase. In contrast, the increase in nitric oxide production in cardiac tissue by doxorubicin was not dose‐dependent with the maximum increase (81%) at a cumulative dose of 10 mg/kg. It is worth mentioning that plasma endothelin‐1 and cardiac nitric oxide were significantly increased at 24 hr after the single dose of 20 mg/kg doxorubicin. The increase of plasma endothelin‐1 and cardiac nitric oxide with the cardiomyopathy enzymatic indices, may point to the conclusion that both endothelin‐1 and cardiac nitric oxide are increased during the development of doxorubicin‐induced cardiomyopathy.     

Physiological disposition of CGS 16617 in rat, dog, and man

The disposition and metabolism of CGS 16617 (3-[(5-amino-1-carboxy-1S-pentyl)amino],2,3,4,5-tetrahydro-2-oxo-3S-1H-1 - benzazepine-1-acetic acid), and angiotensin l-converting enzyme inhibitor, were investigated in rats, dogs, and man. In rats, a single oral dose of 10 mg/kg 14C-CGS 16617 afforded peak plasma concentrations of drug between 0.5 and 6 hr of dosing. The AUC was on average 9.6% of that after iv administration of the same dose, indicating low oral absorption of the drug. The apparent volumes of distribution, V1 and Vdss, were 0.45 and 2.5 liters/kg, respectively. Disappearance of the drug from plasma after the iv dose was biphasic, with mean half-lives of 0.5 and 13 hr, respectively, for the lambda 1 and lambda 2 phases. After single iv doses (10 mg/kg) to dogs and rats, 14CGS 16617 was almost exclusively eliminated by the renal route, with urinary recoveries of greater than 90% of dose. The same dose administered orally gave urinary recoveries of less than 10% of the dose in rats and about 15% in the dog. The remainder of the dose was eliminated in the feces. Bile duct-cannulated rats excreted less than 3% of an oral 10 mg/kg dose in the bile, in 24 hr. In man (N = 4), a single oral dose of 100 mg 14C-CGS 16617 resulted in peak plasma concentrations of 0.02-0.07 microgram of drug eq/ml between 4 and 6 hr of dosing. The mean terminal half-life was estimated at 81 hr.(ABSTRACT TRUNCATED AT 250 WORDS)     

Assessing the Neurotoxic Potential of Methyl Ethyl Ketoxime in Rats

Assessing the Neurotoxic Potential of Methyl Ethyl Ketoximein Rats. SCHULZE, G. E., AND DERELANKO, M. J. (1993). Fundam.Appl. Toxicol. 21, 476–485. The potential of methyl ethyl ketoxime (MEKO) to produce neurotoxicityfollowing acute and subchronic exposure was studed in rats.A Functional Observational Battery, assessment of motor activity,and neuropathology evaluations were conducted in the contextof acute and subchronic toxicity studies. Three independentstudies are reported: a pilot time-effect study designed todetermine the time course and time to peak effect followinga single high dose of MEKO, a single-dose neurotoxicity study,and a subchronic (13-week) repeated-dose neurotoxicity studyin rats. An acrylamide-positive control group was included inthe acute and subchronic studies for comparison with MEKO. Followingan acute oral exposure of MEKO at a dose level of 900 mg/kg,locomotor activity was decreased compared to control with maximumdecreases occurring between 30 and 60 min following oral administration.In the acute study, transient treatment-related changes in easeof cage removal, ease of handling, and in posture and gait wereobserved 1 hr after dosing with 900 mg/kg MEKO, as were significantdepressions in motor activity. Following a single 300 mg/kgdose, transient MEKO-related changes in gait and aerial rightingreflex were noted 1 hr after dosing. All effects were reversiblewithin 24 hr of dosing. The single 100 mg/kg dose of MEKO waswithout observable effects. No acrylamide-related behavioraleffects were noted following a single 50 mg/kg dose. In thesubchronic study, transient treatment-related changes in easeof cage removal, ease of handling, and in posture, gait, andaerial righting were observed at the 400 mg/kg/day dose levelwhen assessments were conducted immediately after dose administration.No consistent behavioral effects were observed prior to dailydose administration even after 13 weeks of exposure, indicatinga lack of cumulative behavioral effect. No consistent behavioralchanges were noted at doses of 125 mg/kg/day and below. Significantdose-related decreases in red cell mass, and increases in methemoglobinlevels, reticulocyte, leukocyte, Heinz body counts, and spleenweights occurred at subchronic MEKO doses of 40 mg/kg/day andhigher. No MEKO-related neuropathological changes occurred.Animals receiving acrylamide at 20 mg/kg/day showed expectedbehavioral and neuropathological changes consistent with peripheralneuropathy. In conclusion, high doses of MEKO can produce transientand reversible changes in neurobehavioral function consistentwith central nervous system (CNS) depression. No evidence ofcumulative neurotoxicity was detected. The hematopoietic systemwas effected at doses which did not produce detectable changesin CNS function.     

MIDD0301 – A first‐in‐class anti‐inflammatory asthma drug targets GABAA receptors without causing systemic immune suppression

We report a 28‐day repeat dose immunotoxicity evaluation of investigational drug MIDD0301, a novel oral asthma drug candidate that targets gamma amino butyric acid type A receptors (GABA_AR) in the lung. The study design employed oral administration of mice twice daily throughout the study period with 100 mg/kg MIDD0301 mixed in peanut butter. Compound dosing did not reveal signs of general toxicity as determined by animal weight, organ weight or haematology. Peanut butter plus test drug (in addition to ad libitum standard rodent chow) did not affect weight gain in the adult mice, in contrast to weight loss in 5 mg/kg prednisone‐treated mice. Spleen and thymus weights were unchanged in MIDD0301‐treated mice, but prednisone significantly reduced the weight of those organs over the 28‐day dosing. Similarly, no differences in spleen or thymus histology were observed following MIDD0301 treatment, but prednisone treatment induced morphological changes in the spleen. The number of small intestine Peyer's patches was not affected by MIDD0301 treatment, an important factor for orally administered drugs. Circulating lymphocyte, monocyte and granulocyte numbers were unchanged in the MIDD0301‐treated animals, whereas differential lymphocyte numbers were reduced in prednisone‐treated animals. MIDD0301 treatment did not alter IgG antibody responses to dinitrophenyl following dinitrophenyl‐keyhole limpet haemocyanin immunization, indicating that systemic humoral immune function was not affected. Taken together, these studies show that repeated daily administration of MIDD0301 is safe and not associated with adverse immunotoxicological effects in mice.     

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.     

1‐Methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine Pretreatment Attenuates Methamphetamine‐Induced Dopamine Toxicity

Abstract: The effects of pretreatment with MPTP (1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine) on the acute and long‐term effects of methamphetamine on striatal dopamine were evaluated in BALB/c mice. Four subcutaneous injections of a non‐toxic dose of MPTP (8 mg/kg, at 2 hr intervals) were followed three days later by a toxic regimen of methamphetamine (four injections of 4 mg/kg, at 2 hr intervals) and mice were sacrificed immediately or three days later. Control mice received saline in place of the MPTP or methamphetamine and mice were observed for acute changes in body temperature, self‐injurious behaviour, and striatal dopamine metabolites, or long‐term changes in striatal dopamine levels, tyrosine hydroxylase immunoreactivity and glial fibrillary acidic protein. It was observed that pretreatment with MPTP protected mice against the acute increase in body temperature caused by the methamphetamine but, at the same time, delayed the occurrence of self‐injurious behaviour following the repeated injections of methamphetamine. Likewise, pretreatment with MPTP attenuated the long‐term depletion of striatal dopamine induced by the methamphetamine as well as the large increase in glial fibrillary acidic protein and the reduction in tyrosine hydroxylase immunoreactivity. The MPTP‐treatment itself did not alter any of these neurotoxic markers. Finally, the acute decrease in 3,4‐dihydroxyphenyacetic acid levels and increased ratio of 3‐methoxytyramine/dopamine observed 60 min. after a single injection of methamphetamine (4 mg/kg) were also attenuated in MPTP‐treated mice. These results are discussed in the context of the hypothesis that the low‐dose treatment with MPTP may modify exchange diffusion across the striatal cell membrane thereby altering the acute and long‐lasting effects of methamphetamine.     

Chronic toxicity of aclacinomycin A in rats (author's transl)

Male and female Wistar rats were treated with aclacinomycin A, a new anthracycline antitumor antibiotic, at 5 dosage levels (0.08, 0.15, 0.3, 0.6 and 1.2 mg/kg/day) by daily intraperitoneal injections for 180 days for a chronic toxicity study. Recovery was also examined for 30 days after completion of the administration. Mortality was as follows: Male 5/24, female 3/24 in 0.6 mg/kg/day dose group and male 19/24, female 8/24 in 1.2 mg/kg/day dose group. Anorexia, depression of spontaneous activity and unformed feces were observed in rats in 0.6 and 1.2 mg/kg/day dose groups after day 90. Body weight gain decreased during the period. No significant change was found in rats receiving the drug at 0.3 and less mg/kg/day all through the observation period. Remarkable decreases in WBC count were noted in rats in the two highest dose groups on day 90. Autopsy findings included atrophy of the thymus and hyperemia and hemorrhage in the gastrointestinal tract and mesenteric lymph node in the animals treated at 0.6 and 1.2 mg/kg/day in the examination on day 90. Histologically, atrophy of the thymus and hyperplasia of the spleen were observed in the higher dose groups on day 90. But no remarkable abnormalities were found in histological examination on day 180. The changes in general symptom and decrease in body weight gain, which were observed during the dosing period in rats in 0.6 mg/kg/day dose group, recovered within 30 days after the drug administration was discontinued but no complete recovery of the WBC count decrease was observed.     

Toxicological Evaluation of the Cardiotonic Isomazole in the Dog

Acute, subchronic, and chronic toxicity studies were conductedin dogs with the new vasodilator/cardiotonic drug isomazole(IMZ) to support, in part, clinical investigations of this agentin humans. Single oral doses of IMZ of 25, 50, or 100 mg/kggiven to English pointer dogs (2/dose) caused a marked dropin systemic blood pressure and reflex-induced increases in heartrate to values well over 200 beats per minute. These responseswere maintained for 12 to 22 hr depending on the dose given.One of the dogs receiving 100 mg/kg died at 4.5 hr postdose.Results of subchronic (3 months) and chronic (1 year) studiesin beagle dogs (4/sex/dose group), in which measurable plasmalevels of the drug and its metabolites were found, indicatedthat IMZ did not produce any discernible adverse findings whengiven in doses up to 16 mg/kg, other than expected cardiotoxiceffects. The plasma t_1/2 of IMZ at 16 mg/kg increased to between4 and 8 hr from 2 hr noted at lower doses. In the 1-year study,at all doses and in both sexes, plasma levels of IMZ declinedover the first month, stabilizing (at the 2 and 6 mg/kg doses)thereafter for the duration of the study. At the high dose of16 mg/kg, after 1 year plasma levels of IMZ exceeded (females)or equaled (males) the 1-month values. At peak plasma levelsof IMZ (2 hr postdose), plasma levels of parent drug increasedlinearly with the dose. The cardiotoxic effects consisted ofsubstantial postdose increases in heart rate throughout thecourse of treatment (5 mg/kg and above), significant increasesin heart weight (6 mg/kg and above), and multifocal myocardialfibrosis (6 mg/kg and above). There was a decline in basal heartrate at doses of 12.5 mg/kg and higher. The results of thesestudies demonstrated that repeated IMZ administration, as expected,was cardiotoxic to the dog, a species relatively sensitive tothe pharmacological activity and hemodynamic changes inducedby vasodilator/cardiotonic drugs. The no-effect dose level forcardiotoxicity in the repeated dose studies was considered tobe 2 mg/kg, the lowest dose tested.     

Age‐Related Differences on Aluminium Mobilization by Chelating Agents in Aluminium‐Loaded Uraemic Rats

The efficacy of deferoxamine, deferiprone, and a combination of these chelating agents in the mobilization and promotion of aluminium (Al) excretion was compared in two age groups of uraemic rats which had previously received Al nitrate nonahydrate intraperitoneally in a daily dose of 45 mg/kg for 5 weeks. At the end of the period of Al exposure, Al‐loaded rats of each age (young and adult) group were given one of the following treatments for 5 days: 0.90 mmol/kg/day of deferoxamine (subcutaneously), 0.90 mmol/kg/day of deferiprone (orally), and 0.45 mmol/kg/day of deferoxamine (subcutaneously) plus 0.45 mmol/kg/day of deferiprone (orally). Control rats were given 0.9% saline (subcutaneously) and deionized water (orally). Total urines were collected 24 hr after each chelator administration. Although young rats treated with deferoxamine, deferiprone, or deferoxamine plus deferiprone showed significant increases in the total amount of Al excreted into urine during 5 consecutive days, the effect of combined administration of deferoxamine and deferiprone was lower than that caused by deferoxamine or deferiprone only. On the other hand, after administration of deferoxamine and deferiprone, a significant reduction of Al was noted only in the liver of young rats, while no significant effects of the chelators were seen in any of the examined tissues of adult animals. The results of the current study show that a combined therapy with deferoxamine and deferiprone (at half‐doses of each drug) can also be effective in mobilizing Al from the body of Al‐loaded uraemic rats.     

Preclinical Toxicity Evaluation of Tepoxalin, a Dual Inhibitor of Cyclooxygenase and 5-Lipoxygenase, in Sprague--Dawley Rats and Beagle Dogs

Tepoxalin [5-(4-chlorophenyl-N-hydroxy-1-(4-methoxyphenyl)-N-methyl-1H-pyrazole-3-propanamide]is an orally active anti-inflammatory agent, which inhibitsboth cydooxygenase and 5-lipoxygenase activities. The oral toxicityof tepoxalin was evaluated in 1- and 6-month rat (up to 50 mg/kg/day)and dog (up to 150 mg/kg bid) studies. In rats, increased liverweight, centrilobular hypertrophy, and hepatic necrosis wereobserved at dosages 20 mg/kg/day. Renal changes indicative ofanalgesic nephropathy syndrome (i.e., papillary edema or necrosis,cortical tubular dilatation) were seen at 15 mg/kg. In ratstreated for 1 month, these hepatic and renal effects were largdyreversible after a 1-month recovery period. Gastrointestinalerosions and ulcers were seen in female rats given 40 mg/kg/dayfor 6 months. Changes in clinical pathology parameters includeddecreases in red blood cell count, hemoglobin, and hematocritmean values; elevation in platelet counts; and an increase inprothrombin and activated partial thromboplastin times. Mildincreases in alanine aminotransferase, aspartate aminotransferase,and cholesterol were also noted in rats. Decreased erythrocyteparameters, increased leukocyte counts, and decreased totalprotein, albumin, and/or calcium were noted in some dogs inthe 300 mg/kg/day group follo 6 months of dosing. Small pyloriculcerations were seen at 100 and 300 mg/kg/day dosages for upto 6 months. In both rats and dogs, no accumulation of tepoxalinor its carboxylic acid metabolite was detected in plasma followingmultiple dosing over a range of 5 to 50 mg/kg/day for rats and20 to 300 mg/kg/day for dogs. Plasma concentrations of the carboxylicacid metabolite were severalfold higher than those of the parentcompound. The no-effect dosages In rats (5 mg/kg/day) and dogs(20 mg/kg/day) were approximately one and six times the ED50(3.5 mg/kg), respectively, for inhibition of inflammatory effectsin the adjuvant arthritic rat without gastric mucosal damage.In terms of severity, the relative lack of gastrointestinalside effects, within the estimated therapeutic dose range, distinguishestepoxalin from most marketed anti-inflammatory drugs.     

Counteraction of the Rapid Tolerance to 8‐Hydroxy‐2‐(di‐n‐propylamino)tetralin‐Induced Hypothermia in Rats by Activation of the GABAA Receptor‐Chloride Channel Complex

Abstract: The effects of compounds that open the GABA_A receptor‐chloride channel complex on the rapidly developed tolerance to the 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin hydrobromide(8‐OH‐DPAT)‐induced hypothermia in rats were examined. The test compound was injected 15 min. before 1 mg/kg subcutaneous 8‐OH‐DPAT or saline and 24 hr later a challenge dose of 0.1 mg/kg subcutaneous 8‐OH‐DPAT was given. The rectal temperature was measured before the challenge dose and 30, 60, 90 and 120 min. thereafter. The hypothermic effect was calculated as the area under the curve. It was found that all the GABAergic compounds examined significantly counteracted the 8‐OH‐DPAT‐induced tolerance to the hypothermic response: muscimol at 3 mg/kg subcutaneous, diazepam at 1 – 3 mg/kg subcutaneous, pentobarbitone sodium at 20 mg/kg subcutaneous, and chlormethiazole at 40 mg/kg subcutaneous. Combined treatment of the rats with the GABA_A receptor antagonist, bicucculine, or the GABA_A receptor‐chloride channel blocker, picrotoxin and diazepam, pentoparbitone sodium or chlormethiazole significantly antagonised this counteraction of the 8‐OH‐DPAT‐induced tolerance. Depletion of 5‐HT by pretreatment of the rats with the tryptophan hydroxylase inhibitor p‐chlorophenylalanine did not counteract the 8‐OH‐DPAT‐induced tolerance to the hypothermic response. Pretreatment of the rats with dexamethazone did not change the development of the tolerance to 8‐OH‐DPAT‐induced hypothermic effect which seems to exclude the involvement of the hypothalamo‐pituitary‐adrenocortical axis in the tolerance development. It is concluded that the results support the hypothesis that GABA neurones beyond the 5‐HT neurones are involved in the mechanism causing tolerance to the 5‐HT_1A receptor‐mediated hypothermia in rats.     

Differential Sensitivity to 8‐Hydroxy‐2‐(di‐n‐propylamino)tetralin‐Induced Corticosterone Secretion and Hypothermia between Sprague‐Dawley Rats from Different Breeding Colonies

Abstract: The sensitivity of Sprague‐Dawley rats from 4 different breeding colonies (ALAB, M&B, B&K, Charles River) and one breeding colony of Wistar rat (M&B) to the 5‐hydroxytryptamine_1A (5‐HT_1A) receptor stimulatory effect of 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin hydrobromide (8‐OH‐DPAT) resulting in corticosterone secretion and hypothermia was compared. The dose‐response curves of the increase in plasma corticosterone showed that ALAB and M&B rats were 3.5 times more sensitive to 8‐OH‐DPAT than B&K and Charles River rats, the Wistar rats being in between. The attenuation of the corticosterone response 24 hr after a single injection of 1 mg/kg 8‐OH‐DPAT was greater for the ALAB and M&B rats than for B&K, Charles River and Wistar rats. The comparison of the 8‐OH‐DPAT‐induced hypothermia in the various rat colonies showed a similar pattern: the sensitivity of ALAB rats was about twice that of M&B, B&K and Wistar rats, Charles River rats being 9 times less sensitive. The attenuation of the response 24 hr after 1 mg/kg 8‐OH‐DPAT measured as the shift in dose‐response showed similar shift factors (4.1 to 6.7) for all rat colonies except for the B&K rats (3.0). The hypothermic response at 0.1 mg/kg 8‐OH‐DPAT was significantly lower for the Charles River and B&K rats than for the ALAB rats. Similarly was the maximal attenuation of the hypothermic effect in these rats less than half of that of the ALAB rats. The possible cause of the observed differences in the response to 8‐OH‐DPAT between these rat colonies is discussed in terms of receptor reserves and the involvement of other transmitter systems in the responses.     

Toxicity study of cefmatilen hydrochloride hydrate (S-1090) (1)--Single oral and intravenous dose toxicity studies in rats

A single oral dose toxicity study of Cefmatilen hydrochloride hydrate (S-1090) and a single intravenous dose toxicity study of its sodium salt (S-1090-Na) were conducted in rats. One dose level of 2000 mg potency/kg was set in both studies. Single oral dose toxicity study of S-1090 No deaths occurred. Diarrhea occurred on the dosing day and slightly soft feces lasted until 6 days after administration. These changes were considered to result from changes of intestinal flora induced by the antibiotic activity of S-1090. Reddish-brown feces (due to chelated products of S-1090 or its decomposition products with Fe3+ in the diet) were also observed until the next day after administration. Body weights increased favorably, and no S-1090-related pathological changes were observed. The oral lethal dose of S-1090 was estimated to be more than 2000 mg potency/kg. Single intravenous dose toxicity study of S-1090-Na No deaths occurred. The rats showed characteristic clinical signs such as hypoactivity, abnormal gait and hypopnea immediately after dosing, and some rats showed prone position or paleness of eyeballs and ear auricles in due course. These signs disappeared by 4 hr after administration. Slightly soft feces and reddish-brown feces were observed much the same as in the orally-treated rats. Body weights increased favorably. In the pathological examinations, slight cecal enlargement and increased basophilia, dilatation and calcification of the renal tubules in the kidney were observed. The intravenous lethal dose of S-1090-Na was estimated to be more than 2000 mg potency/kg.