Chennekatu P. Peter

Norfloxacin: Review of safety studies

The tolerability profile of norfloxacin, the first of a new generation of fluoroquinolone carboxylic acid antibacterials, has been defined in numerous laboratory animal and human trials. Whether administered for moderate or protracted periods, norfloxacin has been relatively safe in animals over a wide range of doses. There has been no evidence of a teratogenic effect in any of the animal species tested (rat, rabbit, mouse, monkey) at six to 50 times the human dose (400 mg twice daily). However, norfloxacin has been shown to produce embryonic loss in monkeys when given in doses 10 times the maximal human dose, resulting in peak plasma levels that are two to three times those obtained in humans. Although there are no adequate and well-controlled studies in pregnant women, norfloxacin is not recommended for use in this population because it, like other drugs in this class, causes arthropathy in immature animals. In animals, norfloxacin is neither mutagenic nor carcinogenic, and, in clinical trials, norfloxacin-related adverse experiences have been uncommon. Those that have occurred have been generally mild, requiring discontinuation of therapy in less than 1 percent of patients. The most frequently reported side effects have been nausea, dyspepsia, headache, and dizziness. Administration of 400 mg of norfloxacin at two or three times a day has been associated with reasonably good gastrointestinal tolerance.

Association between Adverse Maternal and Embryo-Fetal Effects in Norfloxacin-Treated and Food-Deprived Rabbits

Norfloxacin is a new antibiotic which caused embryo-fetal toxicity in association with maternotoxicity when given orally to rabbits at 100 mg/kg/day. The intestinal flora of rabbits is unusually sensitive to many antibiotics and it was suspected that the maternotoxicity and embryo-fetal toxicity caused by oral norfloxacin were secondary to an effect on the intestinal flora. To test this idea, a teratologic study was conducted in which rabbits were dosed on Days 6 to 18 of gestation with norfloxacin given orally at 100 mg/kg/day or subcutaneously at 20 mg/kg/day. The oral treatment caused decreased food consumption (to less than 15 g/day in some animals), body weight loss, an increased resorption rate, and decreased fetal weight. Among the females in the orally dosed group, there was a significant correlation (p less than or equal to 0.005) between the effects on maternal body weight and the resorption rate. The subcutaneous treatment caused little intestinal exposure (biliary excretion = only 2-4% of dose) and no maternotoxicity or embryo-fetal toxicity, even though blood levels of drug were at least as high as those in the oral group. Since the maternotoxicity and embryo-fetal toxicity were specific to the oral route and not correlated with the level of systemic exposure, the maternotoxicity may have been secondary to an effect on the intestinal flora and the embryo-fetal toxicity may have been secondary to the maternotoxicity. The decreased food consumption observed in the oral group may have contributed to the embryo-fetal toxicity since, in a separate study, it was found that lowering the amount of food provided to rabbits on Days 6 to 18 of gestation from 150 g/day to 50 or 15 g/day also caused adverse maternal and fetal effects including, at 15 g/day, fetal malformations.

Spontaneous nephropathies in rats.

Spontaneously occurring diseases of the kidneys are very common in laboratory rats. These diseases include chronic progressive nephrosis, nephrocalcinosis, renal tubular epithelial hyaline droplets, renal tubular hypertrophy, and renal tubular basophilia. As increasing numbers of rats are used in long-term toxicity and carcinogenicity studies, recognizing spontaneously occurring renal lesions and understanding their etiology and pathogenesis are important in making an assessment of the safety of drugs and chemicals that are being tested. The purpose of this paper is to review the incidence, morphology, and pathogenesis of these spontaneous diseases. Some of the factors that alter the incidence and/or severity of these spontaneous diseases will also be discussed.

Leydig Cell Hyperplasia and Adenomas in Mice Treated with Finasteride, a 5α-Reductase Inhibitor: A Possible Mechanism

Finasteride is a selective inhibitor of the enzyme 5 alpha-reductase which is responsible for the conversion of testosterone (T) to dihydrotestosterone (DHT). Finasteride is indicated for the treatment of benign prostatic hyperplasia in man (approximately 0.1 mg/kg/day). The effect of long-term treatment was studied in mice given high doses (2.5, 25, and 250 mg/kg/day) of finasteride for 83 weeks. In finasteride-treated mice, increased incidences of testicular Leydig cell hyperplasia (52% compared to 24% in control group) at doses equal to or greater than 25 mg/kg/day and Leydig cell adenomas (32% compared to 0.5% in control group) at 250 mg/kg/day were observed. There were no drug-related effects on the seminiferous tubules. Since luteinizing hormone (LH) is a trophic hormone for Leydig cells, short-term studies (5 to 14 weeks) were done to investigate the relationship between Leydig cell hyperplasia and serum LH levels in finasteride-treated mice. In these studies, there was a positive correlation between the drug-related increased incidence of Leydig cell hyperplasia and a statistically significant (p < or = 0.05) increase in serum LH levels in finasteride-treated (250 mg/kg/day) mice. Furthermore, studies in castrated male mice showed that the suppression of serum LH levels by T is reversible by inhibition of conversion of T to DHT with finasteride (250 mg/kg/day), supporting the hypothesis that DHT is involved in the regulation of LH release in mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Qualitative and quantitative evaluation of prostatic histomorphology in rats following chronic treatment with finasteride, a 5-alpha reductase inhibitor.

OBJECTIVE To determine any potential direct and/or indirect effects of elevated intraprostatic T levels on the prostates of rats chronically (1-2 years) exposed to high doses (160 mg/kg/day) of finasteride, a selective inhibitor of 5-alpha reductase. METHODS Sprague-Dawley male rats were administered daily finasteride by oral gavage. Prostates from all rats were weighed, fixed in 10% neutral buffered formalin, and processed for light microscopic examination. The volume fractions of the prostatic glandular and stromal compartments were quantitated by morphometric analysis. RESULTS Administration of finasteride at doses of 20, 40, and 80 mg/kg/day for one year resulted in a significant (P < or = 0.05) decrease in prostatic weight; prostatic atrophy was evident by light microscopy. Morphometric analysis of the prostate showed that chronic finasteride administration resulted in a significant (P < or = 0.001) decrease in the absolute volume of both glandular (-65.2%) and stromal (-57.1%) compartments of the prostate. Furthermore, the total number of epithelial and stromal cells per gland were significantly (P < or = 0.002) decreased in finasteride-treated rats compared with vehicle controls; the magnitude of mean decrease was 69.8 percent and 50.6 percent of controls in epithelial and stromal cells, respectively. In addition, prostates from all two hundred fifty rats in a two-year study were qualitatively evaluated by light microscopy. Administration of finasteride at doses ranging from 2.5 mg/kg/day to 160 mg/kg/day for two years did not result in an increase over the background incidence of prostatic focal hyperplasia or adenoma. No malignant tumors of the prostate were seen in any of the groups. CONCLUSIONS These studies have demonstrated that the expected pharmacologic effects of finasteride on the prostate are maintained following chronic treatment and that there was no evidence of a direct and/or an indirect effect of elevated intraprostatic T on prostatic morphology in rats.

The Value of Historical Control Data

Chronic toxicity studies or carcinogenesis bioassays are conducted to assess the potential toxicity or carcinogenic properties of industrial or environmental chemicals or pharmaceutical agents. Such studies are generally performed in both sexes of two rodent species, typically rats and mice, over a period of about 24 months. Chronic toxicity studies are also carried out in larger laboratory animal species, such as monkeys or dogs. The duration of such studies in these species may range from one to five years, or longer. However, this chapter will be concerned with studies in rodents, since by far the greatest number of chronic bioassays are carried out in these species.

Effect of chronic growth hormone administration on skeletal muscle in dogs.

Administration of growth hormone (GH) results in increased body weight gain in dogs. Increased body weight gain is believed to be a result of the trophic effect of GH on the musculoskeletal system. However, edema is one of the side effects described in man following exogenous GH administration. Thus, the objective of this study was to determine if the expected increased weight gain in GH-treated dogs is a result of increased muscle mass. Porcine growth hormone (pGH), administered subcutaneously to beagle dogs at doses of 0.025, 0.1, and 1 IU/kg/day for 14 wk, resulted in elevated serum GH and insulin-like growth factor-1 (IGF-1) levels (see accompanying paper, Prahalada et al). This was associated with a significant increase in body weight gain and weights of the cranial tibialis muscle in both male and female dogs. The increased muscle mass likely contributed to the significant increase in body weight gain seen in both sexes. Quantitative analysis of skeletal muscle sections stained for ATPase activity showed increases in type I (slow twitch) and type II (fast twitch) myofiber sizes in mid- and high-dose males and in high-dose females. The ratio of type I and type II muscle fibers remained unchanged. Hypertrophic myofibers were enlarged but had a normal histologic and ultrastructural organization when observed by light and transmission electron microscopy. The results of this study have demonstrated that increased muscle mass in pGH-treated dogs is related to hypertrophy of muscle fibers and not due to edema. Exogenous GH administration has an anabolic effect on skeletal muscle in dogs.

Rat Urinary Bladder Hyperplasia Induced by Oral Administration of Carbonic Anhydrase Inhibitors

The carbonic anhydrase inhibitors, acetazolamide and MK-0927, were given by oral route to male Sprague-Dawley rats at 200 mg/kg/day and 25 mg/kg/day, respectively, for up to 4 weeks. Sequential necropsies were performed and urinary bladders were examined by light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Similar urinary bladder changes were seen with both compounds. SEM evidenced slight multifocal urothelial changes consisting of cell swelling, dissociation, degeneration, and exfoliation after 3 and 5 days of treatment. After 2 and 4 weeks of treatment, elevated or leafy microridges on the luminal cell surfaces were seen together with foci of swollen cells. After a 2-month-recovery-period, the urothelial surfaces were normal. LM and TEM showed multifocal vacuolation of the urothelium associated with inflammation of the underlying lamina propria after 3 and 5 days of treatment. Cellular hypertrophy and hyperplasia of the transitional epithelium was seen after a 5-day treatment, persisted without increasing severity after 2 and 4 weeks of treatment, and totally regressed after the recovery period. It was concluded that, in the rat urinary bladder, oral administration of acetazolamide and MK-0927 induced early degeneration and inflammation followed by epithelial regeneration, resulting in a reversible hyperplasia of the transitional epithelium.

Spontaneous renal disease in laboratory animals.

Publisher Summary This chapter discusses spontaneously occurring renal diseases in laboratory animals. Spontaneously occurring renal diseases are common in laboratory animals. However, the diseases vary with each species examined. The chapter also discusses the importance of knowing the background disease patterns in laboratory animals. Knowing the background diseases in a species or strain of animal will aid an investigator in selecting or avoiding a given species for experiments. Such knowledge is also important to understand the similarities or differences between animal and human renal diseases. In some cases, the renal diseases in animals are identical to a human disease whereas in other cases, the diseases in animals have no human counterpart. An example of a disease occurring in animals but not in humans is the chronic renal disease of rats. All rat strains develop chronic renal disease. The cause is unknown, but it is rat-specific with no counterpart in humans. The renal anatomy, histology, and physiology of laboratory animals and humans are similar but not identical. Laboratory animals have a single renal papilla in contrast to humans where there are several conical regions called pyramids. Like humans, animals have a uniform tan to brown color and a smooth glistening capsular surface of the kidney. The functional unit of the kidney is the nephron and the distal tubule is connected to a system of collecting ducts. The nephrons and collecting ducts arise from different embryological primordial. The glomerulus consists of a tuft of capillaries enclosed within Bowmans capsule. The capillaries are lined by thin endothelium and a thin visceral layer of epithelium.

Morphological Changes in the Pituitary Gland of Dogs Chronically Exposed to Exogenous Growth Hormone

Growth hormone (GH) synthesis and release from the pituitary is regulated by hypothalamic releasing hormone, insulin-like growth factor-1 (IGF-1), and somatostatin. However, the potential effects of pharmacological doses of exogenous GH on the pituitary are not well studied. To determine the potential chronic effects of exogenous GH on pituitary morphology in dogs, porcine GH (pGH) was administered subcutaneously to 3 groups of dogs (4 animals/sex/group) at doses of 0.025, 0.1, and 1.0 IU/kg/day for 14 wk. A group (4/sex) of dogs served as the vehicle control. The pituitaries from all dogs were weighed and fixed in appropriate fixatives for light and electron microscopic examination; in addition, cells of the pars distalis were quantitated by a point counting method following immunostaining to identify cells containing GH, prolactin (PRL), and adrenocorticotrophic (ACTH) hormones. Administration of pGH resulted in a statistically significant (p ≤ 0.05) increased pituitary weight through the high dose. By light microscopy (LM), hypertrophy of pars distalis cells was evident in mid- and high-dose female dogs. The pituitaries of dogs given the lowest dose (0.025 IU/kg/day) of pGH were not remarkable based on weight and LM findings. In addition, transmission electron microscopic (TEM) examination of the pituitary gland of high-dose dogs demonstrated, in both sexes, pituitary cells with variably dilated rough endoplasmic reticulum and decreased numbers of secretory granules; some of these cells reacted positively to GH immunostaining. Quantitative analysis of the pituitary gland of high-dose males and females showed an increase in the absolute volume of all cell populations studied: GH-, PRL-, and ACTH-positive cells. Based on the LM and TEM findings, the increased volume of the cell populations studied is likely related to cellular hypertrophy. The expected elevation in serum GH levels following repeated administration of pGH and an associated elevation in serum IGF-1 levels resulted in morphologic changes in the pituitary gland of dogs given high doses (≥0.1 IU/kg/day) of pGH; these observations differed from the reported findings in pituitaries of transgenic mice secreting large quantities of bovine GH.