No-effect Dose Research Articles

Clinical teratology

Genetic causes account for 20% to 25% of human birth defects, but the largest proportion of birth defects have no definitive etiology and some of these malformations may be due to intrinsic, "nonpreventable" spontaneous errors of development. Environmental causes, which include maternal disease states, maternal infection, mechanical factors, problems of constraint, chemicals, drugs, and physical agents, are responsible for only about 10% of human birth defects. The scientific basis for understanding the risk of congenital malformations from exposure to environmental agents is based on several tenets of toxicology and embryology dogma. The first tenet is that essentially all teratogens that have been studied have a typical toxicologic dose response relationship and a no-effect dose. Secondly, the stage of gestation is critical to the effects that are expected, and all stages of embryogenesis and fetogenesis can have vulnerability to environmental toxicants. Thirdly, the response of the embryo and fetus is characteristic for each teratogenic agent, although there is some similarity in the effect of certain teratogens. Appropriately designed developmental toxicology studies and basic embryologic and biologic concepts are all used to estimate the potential reproductive hazard for embryonic death, growth retardation, congenital malformation, and functional deficit.

Hexachlorobenzene toxicity in the rat ovary: II. Ultrastructure induced by medium (10 mg/kg) dose exposure

Hexachlorobenzene (HCB) is a known toxicant that is found in the environment as a by-product during manufacture of certain pesticides. This chlorinated chemical has been isolated from many tissues including ovary. When administered in high doses, HCB causes degeneration of primordial germ cells and ovary surface epithelium in sub-human primates. A purpose of this experiment was to determine a no-effect dose of the chemical on the rat ovary. The study is part of a comprehensive investigation on the effects of the compound on the biochemical, hematological, and morphological parameters in the monkey and rat.

Harmonization of Drug Safety Guidelines: A Perspective from the Pharmaceuticals Industry

The Pharmaceutical Manufacturers Association (PMA) and the International Federation of Pharmaceutical Manufacturers Association (IFPMA) have taken a leading role in the current harmonization efforts, which also include issues on quality assurance and clinical efficacy, although these subjects will not be addressed here. Important preclinical testing issues were identified by industry and regulatory expert working groups in Europe, Japan, and the United States. The most critical issues were then selected, and regulatory agencies in each country were encouraged to address the possible resolution of national differences. The issues under discussion include acceptable requirements for single-dose testing in rodents and nonrodents; clarification of no-effect, delayed-effect, and toxic-effect dose levels in repeated-dose toxicity studies; 6-versus 12-month requirements for chronic toxicity studies; clarification and harmonization of requirements for developmental toxicity studies; standards/issues for biotechnology safety studies; and the timing of toxicity studies versus the conduct of clinical trials. Final resolutions and agency positions were presented during the First International Conference on Harmonization held November 5–7 in Brussels, Belgium.

Reproductive and developmental toxicity study of prednisolone farnesylate (PNF)--study by subcutaneous administration of PNF prior to and in the early stages of pregnancy in rats

A fertility study of Prednisolone farnesylate (PNF), a newly synthesized corticosteroid, was conducted in Sprague-Dawley rats. This compound was administered subcutaneously at dose levels of 0(control), 0.04, 0.2 and 1 mg/kg/day to males for 63 days before mating and during the mating period, and to females for 14 days before mating, through the mating period and until day 7 of pregnancy. Each 24 male and female rats were mated, and females were killed on day 20 of pregnancy to examine their fetuses. 1. In the parental animals, loss of fur or thin fur and incrustation of treated site occurred in male rats treated at doses of 0.2 mg/kg or more and female rats treated at dose of 1 mg/kg, and at the same dose groups, the thinning of skin, atrophy of the thymus and intention of the substance at the injected site were noted. Moreover, body weight gains and food consumption were suppressed in both sexes treated at the dose of 1 mg/kg. 2. Fertility and reproductive ability in both sexes, and estrus cycles in female rats were not affected by administration of PNF. 3. In the fetuses, no embryonic or fetal lethal effect and teratogenic effect were noted. From these results, the no-effect dose levels of PNF on the parental general states, the parental reproductive ability and those of the fetuses are thought to be 0.04 mg/kg/day, 1 mg/kg/day or more and 1 mg/kg/day or more, respectively, under the experimental conditions of this study.

Reproductive and developmental toxicity study of prednisolone farnesylate (PNF)--study by subcutaneous administration of PNF during the period of fetal organogenesis in rats

A teratogenicity study of Prednisolone farnesylate (PNF), a newly synthesized corticosteroid, was conducted in Sprague-Dawley rats. This compound was administrated subcutaneously to female rats at dose levels of 0(control), 1, 5 and 25 mg/kg/day, once a day, for 11 days from day 7 to day 17 of pregnancy. In each dose group, 26 or 27 dams were killed on day 20 of pregnancy to examine their fetuses. The remaining 14 or 15 dams of each group were allowed to litter naturally, and observations were made on the postnatal growth and development of their offspring. 1. In the dams treated at doses of 1 mg/kg or more, decreased body weight gains and food consumption and retention of the substance at the injected site were noted. However, general signs, parturition, lactation and nursing behaviors were not affected by the administration of PNF. 2. In the F1 fetuses, no embryonic or fetal lethal effect, fetal retardation and teratogenic effect were noted. 3. In the F1 newborns, the postnatal growth, development, responses, behaviors, learning ability and reproductive ability were not influenced. Additionally, no embryonic or fetal abnormalities of their fetuses (F2) were detected. From these results, the no-effect dose levels of PNF on the parental general states, the parental reproductive ability and those of the F1 offspring are thought to be less than 1 mg/kg/day, 25 mg/kg/day and 25 mg/kg/day, respectively, under the experimental conditions of this study. Moreover, the F2 fetuses are not affected by doses up to 25 mg/kg/day of PNF.

Reproductive and developmental toxicity study of prednisolone farnesylate (PNF)--study of subcutaneous administration of PNF during the perinatal and lactation periods in rats

The effects of Prednisolone farnesylate (PNF), a newly synthesized corticosteroid, administrated during the perinatal and postnatal periods were studied in Sprague-Dawley rats. This compound was injected subcutaneously to female rats at dose levels of 0(control), 0.05, 0.5 and 5 mg/kg/day, once a day, for the period from day 17 of pregnancy to day 21 after parturition. Twenty-two to 25 dams in each dose group were allowed to litter naturally, and observations were made on the postnatal growth and development of their offspring. 1. In the dams treated at doses of 0.5 and 5 mg/kg, decreased body weight gains, atrophy of the thymus and retention of the substance at the injected site were noted. However, general signs, food consumption, parturition, lactation and nursing behaviors were not affected by the administration of PNF. 2. In the F1 newborns, the postnatal growth, development, responses, behaviors, learning ability and reproductive ability were not influenced. Additionally, no embryonic or fetal abnormalities of their fetuses (F2) were detected. From these results, the no-effect dose levels of PNF on the parental general states, the parental reproductive ability and those of the F1 offspring are thought to be 0.05 mg/kg/day, 5 mg/kg/day or more and 5 mg/kg/day or more, respectively, under the experimental conditions of this study. Moreover, the F2 fetuses are not affected by doses up to 5 mg/kg/day of PNF.

Reproductive and developmental toxicity studies of 6-amidino-2-naphthyl 4(-)[(4,5-dihydro-1H-imidazol-2-yl) amino] benzoate dimethanesulfonate (FUT-187). (IV)--Oral administration to New Zealand white rabbits during the period of fetal organogenesis.

Oral administration of 6-amidino-2-naphthyl 4(-)[(4,5-dihydro-1H-imidazol-2-yl)amino] benzoate dimethanesulfonate (FUT-187) at doses of 10, 30 and 100 mg/kg was given to New Zealand White rabbits on days 6 to 18 of gestation. The following results were obtained. Decreased food consumption and suppression of body weight gain in dams were observed and these changes contributed to the increase in aborted or prematured births and increased fetal mortality at the 100 mg/kg group. There were changes attributable to FUT-187 on external, skeletal and visceral examinations of fetuses. Based on the above, the no-effect dose level in dams and fetuses in the present study is 30 mg/kg/day.

Reproductive and developmental toxicity study of 6-amidino-2-naphthyl 4(-)[(4,5-dihydro-1H-imidazol-2-yl) amino] benzoate dimethanesulfonate (FUT-187). (II)--Oral administration to rats during the period of fetal organogenesis (prenatal examination)

6-Amidino-2-naphthyl 4(-)[(4,5-dihydro-1H-imidazol-2-yl) amino] benzoate dimethanesulfonate (FUT-187) was given orally to pregnant Crj : CD (Sprague-Dawley) rats from days 7 through 17 of gestation at dose levels of 50, 200 and 800 mg/kg/day. In the 800 mg/kg/day group, salivation just after dosing, suppression in body weight gain and decreased food consumption were observed. No external, visceral and skeletal anomalies attributable to FUT-187 were observed in fetuses. From the present result, it is considered that the no-effect dose level of FUT-187 for dams and fetuses are 200 mg/kg/day and 800 mg/kg/day respectively.

Neurotoxicity of 1-Methoxycycloheptatriene - A Purkinje Cell Toxicant

The toxicity of 1-methoxycycloheptatriene (1-MCHT), a sensory irritant, has been investigated in beagles. It was found to produce gross inco-ordination of the limbs at intravenous doses greater than 10 mg kg-1. The main histological abnormalities were in the cerebellum and consisted of Purkinje cell death and subsequent reactive gliosis. A few necrotic neurons were seen in the diencephalon, pons and medulla. Haematological abnormalities, e.g. leucocytosis with relative lymphopenia, were seen, while biochemical changes included hyperglycaemia and a rise in plasma aminotransferases. The no-effect dose for the histological and biochemical changes was the same. These abnormalities are compared with cerebellar changes observed in acrylamide and other toxic states.

The concept of the acceptable daily intake: An historical review∗

In the first section the sequence of events is outlined which leads to the author's proposal to consider the concept of acceptable daily intake (ADI) for pesticide residues. He developed his theory referring to specific aspects during meetings with experts on the toxicological evaluation of chemical agents which become introduced into foodstuffs intentionally or unintentionally. These meetings were organized periodically by the European Council or Joint FAO/WHO Expert Committees on food additives (JECFA) or pesticide residues (JMPR). The general principles of the ADI evaluation are briefly described as being based on the determination (after extended absorption) of a no-effect dose level in an appropriate animal species; followed by the application, for the extrapolation of the results in animals to humans, of safety factors taking into account the interspecies sensitivity variations and individual sensitivity variations in the groups of essentially heterogeneous human consumers. It is pointed out that the ADI value, which depends on a series of factors, is not a constant, but a guide serving to calculate the admissible limits of diverse chemical agents incorporated in foodstuffs. It must take into account the usual normalities between medium terms of consumption varying a lot with the countries and the various consumer groups. It is clearly noted that, because of the fluctuations in the type and the quantities of absorbed diets, the ADI is in reality an integrated value with regard to the time, a notion that is often forgotten. Other ideas are developed, in particular on the adoption of a temporary ADI and on the concept of a non-specified ADI.

Final Report on the Safety Assessment of Steapyrium Chloride and Lapyrium Chloride

Steapyrium Chloride and Lapyrium Chloride are quaternary ammonium salts used in cosmetic products as biocides or as antistatic agents at concentrations equal to or less than 5.0%. The oral LD50 of Steapyrium Chloride was estimated to be 8.2 g/kg. Subchronic studies in rats established a no-effect dose of 100 mg/kg. Only a very slight dermal irritation was produced on abraded or intact rabbit skin by 1.0% Steapyrium Chloride. A 50% solution of Lapyrium Chloride produced slight to moderate erythema under occluded conditions. Very slight ocular irritation was produced in the eye of the rabbit by a solution containing 1.0% Steapyrium Chloride. Steapyrium Chloride was nonmutagenic when tested in a Salmonella/microsome assay, both with and without activation. Steapyrium Chloride was neither an irritant nor sensitizer when tested at 100% concentration in a repeat insult occluded patch test on 164 individuals. Steapyrium Chloride does not absorb light in the UVA or UVB range and, therefore, would not be expected to be a phototoxic agent. Only limited formulation safety test data were available for Lapyrium Chloride. However, the structural characteristics of Lapyrium Chloride and Steapyrium Chloride are very similar. Therefore, the safety test data on Steapyrium Chloride were used for the safety evaluation of both compounds. On the basis of the available data in this report, it is concluded that Steapyrium Chloride and Lapyrium Chloride are safe as cosmetic ingredients.

Cocaine as a cause of congenital malformations of vascular origin: Experimental evidence in the rat

Cocaine hydrochloride was administered to pregnant Sprague-Dawley rats as a single intraperitoneal dose or as two doses 1-4 hours apart. A single dose administered on day 16 of gestation was teratogenic in a dose-dependent manner, with 40 mg/kg being a no-effect dose and 50 mg/kg the lowest teratogenic dose; 80 mg/kg was lethal to the dam. Forty-eight hours after exposure to a teratogenic dose on day 16 of pregnancy, the fetuses showed severe hemorrhage and edema in the their extremities, particularly the footplates, tail, genital tubercle, and upper lip/nose. When the fetuses were examined on day 21 of gestation, the main externally visible malformations were reduction deformities of the limbs and tail. When two doses of cocaine were administered 1-4 hours apart, the incidence of affected fetuses increased as the time interval between the two doses decreased. Two doses of cocaine administered 2 hours apart were not teratogenic on day 9, 10, 11, 12, 13, or 14 of gestation but did induce reduction deformities on days 15, 16, 17, 18, or 19. The same dose administered 1 hour apart was teratogenic on days 14-19. In general, cocaine administration on gestational days 14, 15, or 16 induced more severe and more widespread hemorrhage and edema than administration on days 17, 18, or 19. In the latter cases, damage was restricted to the distal parts of the hindlimb digits and the tail. The results show that in the rat cocaine is only teratogenic during the late organogenic or postorganogenic period.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative toxicology of temelastine: A novel H 1 antagonist in dog, rat, and monkey

The toxicity of temelastine 2-[4-(5-bromo-3-methylpyrid-2-yl)butylamino]-5-[(6-methylpyrid-3-yl) methyl]-4-pyrimidone a potent, selective, competitive histamine H 1-receptor antagonist was examined in dogs and rats. The major toxicological response seen in the dog was marked, but intermittent and reversible, increases in the plasma activity of a number of liver-associated enzymes, viz alanine aminotransferase (ALT), glutamate dehydrogenase (GLDH), and alkaline phosphatase (ALP). The increases first seen in two male dogs treated for 30 consecutive days at a dose of 300 mg/kg became apparent at lower doses, i.e., 100 and 33.3 mg/kg/day, in 6- and 12-month studies. Although the increases were suggestive of hepatotoxicity, the only histological changes were increases in hepatocellular lipofuscin pigment and foci of macrophages seen in dogs treated at 300 mg/kg for 12 months. Rats treated for up to 12 months at doses as high as 300 mg/kg/day showed no treatment-related increases in plasma enzymes although increases in liver weights and hepatocellular lipofuscin pigment together with centrilobular hypertrophy were seen in the 300 mg/kg/day treatment group. To investigate differences in hepatic responsiveness between species dogs, rats, and monkeys were exposed to high concentrations of temelastine by continuous 24-hr intravenous infusion. The results of the study showed the dog to be most sensitive to the hepatic effects of temelastine. The major toxicological effect of temelastine in the rat was a histopathological lesion of the thyroid gland characterized by agglomeration and depletion of colloid, follicular epithelial hypertrophy and reduced follicular size. The no-effect dose for this lesion was between 10 and 33.3 mg/kg/day. These histopathological changes, characteristic of a “TSH-driven” thyroid gland, were not seen in the thyroid glands of dogs.

REPRODUCTIVE AND DEVELOPMENTAL TOXICITY STUDIES OF BUSPIRONE HYDROCHLORIDE (II) : Oral Administration to Rats During Perinatal and Lactation Periods

Buspirone hydrochloride (buspirone), an anxiolytic drug, was administered orally to pregnant Crj: CD (Sprague-Dawley) rats from day 17 of gestation through day 20 of postpartum at dose levels of 2, 12 and 75 mg/kg/day. The summarized results obtained are as follows: 1. Decreased activity was observed for F0 dams at buspirone 75 mg/kg. Further, the suppression of maternal body weight gains accompanied by the reduction of food consumption was shown during the administration period at buspirone 12 mg/kg and higher. 2. Brain and adrenal weights were increased in F0 dams at buspirone 12 mg/kg and higher. Besides, lung and pituitary weights were augmented in F0 dams at buspirone 75 mg/kg. 3. Buspirone 75 mg/kg brought the increased number of stillbirths in F1 neonates. 4. Buspirone 75 mg/kg lowered the viability of newborns (F1) on postnatal day 3 and prolonged the days required for pinnae detachment, presence of abdominal hair and eye opening in offspring (F1), but failed to function their learning ability, motility, motor activity or emotional development. 5. Body weight gains were depressed in both male and female F1 rats at buspirone 12 mg/kg and higher. Food consumption was also decreased in both sexes at the same dose levels. 6. Heart weights were decreased in female F1 rats after mating at buspirone 12 mg/kg and higher. Further, buspirone 75 mg/kg brought a suppression of brain weights at 10 weeks of age in male and female F1 rats, but failed to affect their reproductive ability. 7. F2 neonates derived from F1 rats whose dams had ever received buspirone during the perinatal and lactation periods showed no changes in observation items at birth. Based on these results, the no-effect dose level of oral buspirone under the present experimental condition was estimated to be 2 mg/kg/day against dams and their offspring.

Untersuchung der subakuten Toxizität von Glucosylthiazolidin‐4‐carbonsäure an Ratten

Glucosylthiazolidine-4-carbonic acid, an intermediate of the Maillard reaction between D-glucose and L-cysteine, was given in doses of 0, 25, 50 or 100 mg/kg b.w. by oral intubation to male and female rats for 21 days. General appearance, growth, food consumption, haematology, urine analysis and serum chemistry including determinations of enzyme activities, organ weights and macroscopic and microscopic pathology were used as criteria for adverse effects. Effects on the kidneys were indicated by oliguria and decreased specific gravity of the urine in males and histopathological changes of the proximal tubules in females. The no-effect dose established from this study is 25 mg/kg b.w.

REPRODUCTIVE AND DEVELOPMENTAL TOXICITY STUDIES OF BUSPIRONE HYDROCHLORIDE (I) : Oral Administration to Rats During the Period of Fetal Organogenesis

Buspirone hydrochloride (buspirone), an anxiolytic drug, was administered orally to pregnant Crj: CD (Sprague-Dawley) rats from day 7 through 17 of gestation at dose levels of 2, 12 and 75 mg/kg/day. The summarized results obtained are as follows: 1. Decreased activity was observed for F0 dams at buspirone 75 mg/kg. Further, the suppression of maternal body weight gains accompanied by the reduction of food consumption was shown during the administration period at the same dose level. 2. Liver weights were increased in F0 dams at term at buspirone 12 mg/kg and higher. Besides, brain, pituitary, adrenal and ovarian weights were increased in F0 dams at term at buspirone 75 mg/kg. 3. Buspirone 75 mg/kg brought the inhibition of fetal growth followed by the lowered values in fetal weights, crown-rump distances and tail lengths. Furthermore, the elevated incidence of skeletal abnormalities such as nodular and wavy ribs and unossified 5th and 6th sternum , as well as retarded ossification of cervical vertebrae, forelimbs and hindlimbs were also noted in this dose level. Also, the retarded ossification was observed at 12 mg/kg. 4. Buspirone failed to affect the parturition of F0 dams. 5. Buspirone did not function the viability of newborns (F1), and postnatal differentiations, learning ability, motility, motor activity or emotional development in F1 animals. 6. Body weight gains were depressed in female F1 rats from 4 to 9 weeks of age and food consumption was decreased in male F1 rats from 6 to 8 weeks of age at buspirone 75 mg/kg. 7. Buspirone 75 mg/kg produced suppressions of brain weights at 10 weeks of age in male and female F1 rats and lung weights at weaning in male F1 rats. Spleen weights were increased in female F1 rats at 10 weeks of age at the same dose level. However, buspirone failed to affect their reproductive ability. 8. F2 neonates derived from F1 rats whose dams had ever received buspirone during the period of fetal organogenesis showed no changes in observation items at birth. Based on these results, the no-effect dose level of oral buspirone under the present experimental condition was estimated to be 2 mg/kg/day against dams and their offspring.

THREE-MONTH ORAL SUBACUTE TOXICITY STUDY OF MOFEZOLAC (N-22) IN RATS

A three-month oral subacute toxicity study of mofezolac (N-22), a non-steroidal anti-inflammatory agent, was performed using dose levels of 6, 20, 60 and 200 mg/kg in rats, and recovery was also assessed one month after withdrawal. 1. Toxic signs caused by N-22 administration, observed only in the 200 mg/kg group, were as follows: soiling around the mouth and/or nose, piloerection, anemia, diarrhea, emaciation and decreased spontaneous locomotor activity. Nine males and thirteen females in the 200 mg/kg group excreted bloody diarrhea and died of general exhaustion between weeks four and thirteen of study. 2. In the 200 mg/kg group, decrease in food consumption and suppression of body weight gain were noted in males from about week four and in females from about week six after initiation of administration, and increase in water consumption was noted in males from about week seven. 3. Urinary examination revealed a decline in urinary pH in males of the 20 mg/kg and above groups and elevation of urobilinogen levels in males of the 60 and 200 mg/kg groups. 4. Hematological examination showed decreases in erythrocyte count (RBC), hematocrit value (Ht) and hemoglobin concentration (Hb) and increase in reticulocyte rate in both sexes of the 200 mg/kg group and an increase in neutrophil rate in males of the 200 mg/kg group. 5. Biochemical examination demonstrated a decrease in chloride (Cl-) in males receiving the 20 mg/kg or above doses and a decrease in calcium (Ca++) in males of the 60 and 200 mg/kg groups. Moreover, there were decreases in cholinesterase (ChE) activity, total protein (TP) and albumin (Alb) values, as well as increases in blood urea nitrogen (BUN), uric acid (UA) and potassium (K+) in both sexes of the 200 mg/kg group, along with elevations in GOT and lactate dehydrogenase (LDH) activities in females of the 200 mg/kg group. 6. The absolute and/or relative organ weights for liver, kidneys, spleen and adrenals were increased in the 200 mg/kg group. 7. On pathological examination, perforating ulceration in the jejunum and ileum, turbid ascites, adhesion and inflammatory changes in capsules of the abdominal organs, splenomegaly, mesenteric lymph node hyperplasia and inflammatory changes in the thoracic cavity were observed in dead animals of the 200 mg/kg group. Similar pathological changes were observed in a few survival cases of the 200 mg/kg group. 8. After a one month recovery period, the above-mentioned changes had mostly recovered, indicating that they were reversible.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicological evaluation of the cardiotonic isomazole in the dog

Acute, subchronic, and chronic toxicity studies were conducted in dogs with the new vasodilator/cardiotonic drug isomazole (IMZ) to support, in part, clinical investigations of this agent in humans. Single oral doses of IMZ of 25, 50, or 100 mg/kg given to English pointer dogs (2/dose) caused a marked drop in systemic blood pressure and reflex-induced increases in heart rate to values well over 200 beats per minute. These responses were 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) studies in beagle dogs (4/sex/dose group), in which measurable plasma levels of the drug and its metabolites were found, indicated that IMZ did not produce any discernible adverse findings when given in doses up to 16 mg/kg, other than expected cardiotoxic effects. The plasma t 1 2 of IMZ at 16 mg/kg increased to between 4 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 declined over the first month, stabilizing (at the 2 and 6 mg/kg doses) thereafter for the duration of the study. At the high dose of 16 mg/kg, after 1 year plasma levels of IMZ exceeded (females) or equaled (males) the 1-month values. At peak plasma levels of IMZ (2 hr postdose), plasma levels of parent drug increased linearly with the dose. The cardiotoxic effects consisted of substantial postdose increases in heart rate throughout the course of treatment (5 mg/kg and above), significant increases in heart weight (6 mg/kg and above), and multifocal myocardial fibrosis (6 mg/kg and above). There was a decline in basal heart rate at doses of 12.5 mg/kg and higher. The results of these studies demonstrated that repeated IMZ administration, as expected, was cardiotoxic to the dog, a species relatively sensitive to the pharmacological activity and hemodynamic changes induced by vasodilator/cardiotonic drugs. The no-effect dose level for cardiotoxicity in the repeated dose studies was considered to be 2 mg/kg, the lowest dose tested.

Effect of CI-949 and CI-959 on immune function and lymphoid organs in rats

The immunotoxic properties of two experimental antiallergic drugs, CI-949 and CI-959, were investigated. Wistar rats were gavaged once (CI-949) or twice (CI-959) daily for 21 days with the drugs. Immunotoxicity was assessed using the enzyme-linked immunoabsorbant assay (ELISA) for humoral immunity, a delayed-type hypersensitivity (DTH) procedure for cell-mediated immunity, and natural killer cell (NKC) activity to evaluate spontaneous cytotoxicity. Ratios of body weight to spleen, thymus, liver and kidney weights were determined. Routine histopathology was performed on lymphoid tissue and other body organs. Although 100 mg/kg/day of CI-949 had some stimulating effect on antibody production and NKC cytotoxicity, no consistent immunomodulation was apparent. Except for a significant increase in liver weight at the 100 mg/kg dose of CI-949, no other toxic effects were observed. In contrast to CI-949, CI-959 significantly ( P<0.05) suppressed antibody production at the 100 mg/kg dose and impaired the DTH reaction, although not significantly. Natural killer cell cytotoxicity was unaffected by 100 mg/kg CI-959. Decreased body weight and histopathological lesions were observed in the thymus and spleen of rats administered 100 mg/kg CI-959. These lesions ranged from mild to severe lymphoid depletion which was also reflected in significantly ( P<0.05) reduced spleen and thymus organ weight to body weight ratios. Since 100 mg/kg of CI-959 produced toxicological and pathological alterations in the exposed rats, these data suggest that CI-959 is not highly or specifically immunotoxic at dosages lower than those that alter conventional toxicological parameters used in new drug testing programs. The no-effect dose for both drugs in these experiments was 30 mg/kg, since all changes noted occurred at the 100 mg/kg level. However, additional studies are necessary to establish a maximal no-observable-effect dose level.

Toxicological Evaluation of the Cardiotonic Isomazole in the Dog

Acute, subchronic, and chronic toxicity studies were conducted in dogs with the new vasodilator/cardiotonic drug isomazole (IMZ) to support, in part, clinical investigations of this agent in humans. Single oral doses of IMZ of 25, 50, or 100 mg/kg given to English pointer dogs (2/dose) caused a marked drop in systemic blood pressure and reflex-induced increases in heart rate to values well over 200 beats per minute. These responses were 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) studies in beagle dogs (4/sex/dose group), in which measurable plasma levels of the drug and its metabolites were found, indicated that IMZ did not produce any discernible adverse findings when given in doses up to 16 mg/kg, other than expected cardiotoxic effects. The plasma t1/2 of IMZ at 16 mg/kg increased to between 4 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 declined over the first month, stabilizing (at the 2 and 6 mg/kg doses) thereafter for the duration of the study. At the high dose of 16 mg/kg, after 1 year plasma levels of IMZ exceeded (females) or equaled (males) the 1-month values. At peak plasma levels of IMZ (2 hr postdose), plasma levels of parent drug increased linearly with the dose. The cardiotoxic effects consisted of substantial postdose increases in heart rate throughout the course of treatment (5 mg/kg and above), significant increases in heart weight (6 mg/kg and above), and multifocal myocardial fibrosis (6 mg/kg and above). There was a decline in basal heart rate at doses of 12.5 mg/kg and higher. The results of these studies demonstrated that repeated IMZ administration, as expected, was cardiotoxic to the dog, a species relatively sensitive to the pharmacological activity and hemodynamic changes induced by vasodilator/cardiotonic drugs. The no-effect dose level for cardiotoxicity in the repeated dose studies was considered to be 2 mg/kg, the lowest dose tested.