Preclinical safety profile of sildenafil.

Sildenafil citrate, marketed as Viagra, for the treatment of erectile dysfunction, has a proven record of safety in humans as predicted by the results of extensive pharmacological and toxicological testing in animals and in vitro, and confirmed by pharmacokinetic exposure data. The aim of this paper is to review succinctly the main findings resulting from these experiments. Daily doses of sildenafil, within and far beyond the human therapeutic range, were given to dogs and rodents for up to 1 and 2 y, respectively. Plasma analyses were conducted to determine the exposure to sildenafil. We found species-specific effects in dogs (Beagle pain syndrome), mice (marked intestinal dilatation) and rats (adaptive reversible hepatocellular hypertrophy associated with secondary thyroid hypertrophy). All these effects in rodents and dogs have no relevance to humans. Morphometric thickness measurements of the retinal layers carried out in response to clinical observations of visual disturbances in humans indicated no difference between treated and control rats and dogs after up to 24 months of treatment. There was no evidence of histopathologic damage to any structures of the visual pathway. Sildenafil had no effects on fertility, no teratogenic potential, was not genotoxic and has no carcinogenic potential. In rats and dogs, safety ratios were 40:1 and 28:1, respectively, in terms of exposure over 24 h (AUC24 h) and 19:1 and 8:1, respectively, in terms of peak plasma concentration (Cmax). These safety ratios illustrate the separation between exposure to sildenafil of animals at large nontoxic doses and the much smaller human therapeutic exposure. This profile highlights the very low risk of human toxicity for sildenafil. The favourable results of the nonclinical safety evaluation of sildenafil in established animal models have been confirmed by many years of clinical experience during the development and marketing of sildenafil.

Straelensiosis in dogs: a newly described nodular dermatitis induced by Straelensia cynotis.

A distinctive nodular dermatitis induced by Straelensia cynotis, a newly described trombidioid larval mite which resides in hair follicles, was identified in 12 dogs living in France. They all had scattered, small (1 to 3 mm in diameter), pale, firm skin nodules, variable in distribution but always affecting the dorsal regions of the head and trunk; they were distributed over the whole body of seven of the dogs. The animals were otherwise healthy except for three severely infested fox terriers which had a decreased appetite, were lethargic, and whose skin nodules were painful to the touch. The nodules did not induce pruritus. The lesions usually began as erythematous papules which developed into firm pale nodules. The dermatitis resolved within two to 12 months. Topical acaricides were ineffective but the skin nodules regressed after treatments with systemic avermectins. Histologically, each nodule was composed of a dilated follicular ostium containing a well-preserved larval mite, and showed a pseudoepitheliomatous follicular hyperplasia and an abundant perifollicular mucinosis. The larvae were identified as belonging to the genus Straelensia (Acari: Leeuwenhoekiidae). It was clearly established that the three fox terriers had become infested within a fox's den. The nymphs and adults of this species of mite are believed to live in foxes' dens; foxes are considered to be the natural host for the larval stage, and dogs a permissive but occasional host.

Multiple pigmented cutaneous papules associated with a novel canine papillomavirus in an immunosuppressed dog.

Cutaneous papillomavirus infection was diagnosed in a 6-year-old female Boxer dog that was under long-term corticosteroid therapy for atopic dermatitis. Multiple black, rounded papules were present on the ventral skin. Spontaneous regression occurred within 3 weeks after cessation of corticosteroids. Histologically, the lesions consisted of well-demarcated cup-shaped foci of epidermal endophytic hyperplasia with marked parakeratosis. In the upper stratum spinosum and in the stratum granulosum, solitary or small collections of enlarged keratinocytes were observed with basophilic intranuclear inclusion bodies and a single eosinophilic fibrillar cytoplasmic inclusion. Ultrastructurally, viruslike particles (40-45 nm in diameter) were observed within the nucleus, free or aggregated in crystalline arrays. Undulating fibrillar material, thought to be a modified keratin protein, was observed in the cytoplasmic inclusion. Immunohistochemistry, restriction enzyme analysis, and molecular hybridization experiments indicated that these distinctive clinical, histologic, and cytologic features were associated with a novel canine papillomavirus.

Fatal transplacental neosporosis in a deer (Cervus eldi siamensis).

Neospora caninum tissue cysts were found in sections of the brain from a full-term stillborn deer of Eld (Cervus eldi siamensis) from a zoo in France. There was N. caninum-associated nonsuppurative encephalitis and the diagnosis was confirmed in immunohistochemical staining with antibodies specific to N. caninum.

Histochemical study of cutaneous mucins in hypothyroid dogs.

A dermal mucinosis, visualized as dermal alcianophilic material, is occasionally present in canine hypothyroidism (myxedema). Various histochemical reactions (alcian blue/periodic acid-Schiff [PAS], alcian blue at pH 2.6, alcian blue at pH 1.0, critical electrolytical concentrations with and without dimethylsulfoxide, differential hydrolysis by hyaluronidases) were performed on skin biopsies from six dogs (four females and two males ranging from 8 to 13 years) affected by hypothyroidism, all of them presenting dermal mucinosis in hematoxylin and eosin-stained sections. In these dogs, the only polysaccharidic compound involved in the dermal mucinosis was hyaluronic acid. In this study, hyaluronic acid dermal deposits of hypothyroid dogs were significantly different from those of controls in subepidermal connective tissue and loose reticular connective tissue but not in periadnexal zones. We recommend the combined alcian blue/PAS reaction as a routine technique to assess dermal mucinosis in hypothyroid dogs.

Human carcinogenic risk assessment based on hormonal effects in a carcinogenicity study in rats with the antifungal agent, fluconazole.

Fluconazole is an orally active bis-triazole antifungal agent that acts by selective inhibition of lanosterol 14 alpha-demethylase, a key enzyme for maintenance of the fungal cell wall. It is not genotoxic. In a 2 year carcinogenicity study in Sprague-Dawley rats, fluconazole decreased mammary fibroadenomas in females and adrenal pheochromocytomas in males, and increased hepatic adenomas in males. The pattern of these changes is explicable in terms of a hormonal imbalance, corroborated in other studies with fluconazole in rats by changes in the weights of hormone-sensitive organs and circulating levels of 17 beta-estradiol. The decreases in mammary tumors are probably a consequence of aromatase inhibition by fluconazole at high dose levels. The tumor effects observed in this study are extremely unlikely to be of relevance to humans, since the hormone effects observed in this study do not occur in humans treated with therapeutic dose levels of fluconazole. This study illustrates the importance of seeking a mechanistic interpretation of rodent tumor findings, which may then be assessed for its relevance to the clinical use of a drug.

Fat, frail and dying young: survival, body weight and pathology of the Charles River Sprague-Dawley-derived rat prior to and since the introduction of the VAFR variant in 1988.

Trends in survival and body weight were evaluated in 2140 control Sprague-Dawley-derived [Crl: COBS-CD(SD)BR and Crl: COBS-VAF CD(SD)BR] rats used for 24-month rat carcinogenicity studies between 1979 and 1991. Body weight and survival were remarkably stable in the CD-COBS rats used during 1979-1987: at 24 months, the mean survival in males was 68 +/- 5%, and 60 +/- 5% in females. With the CD-COBS-VAF rat, a variant of the CD-COBS strain used between 1988 and 1991, the survival at 24 months dropped to 41 +/- 3% in males, and 44 +/- 7% in females compared to the CD-COBS. The CD-COBS-VAF rat had a significantly reduced life span (P < 0.001 at 24 months), a significant increase in mean body weight (males at 6 months: 672 +/- 24 g vs. 536 +/- 6 g; females: 359 +/- 7 g vs 308 +/- 3 g; P < 0.001) and food consumption (males at 6 months: 31.3 +/- 3.3 vs. 25.4 +/- 2.1 g d-1; females: 22.0 +/- 2.7 g v. 20.3 +/- 2.0 g d-1; P < 0.001). CD-COBS-VAF rats which failed to survive up to study termination had individual body weights at 3, 6 and 12 months which were significantly higher (P < 0.001) than those which survived until 24 months. Our historical data base of control rats (CD-COBS and CD-COBS-VAF) in carcinogenicity studies revealed a significant (males: P < 0.001); females: P < 0.01) and inverse linear relation between mean 3-month body weight and 24-month survival. When compared to CD-COBS animals, CD-COBS-VAF rats showed an increase in the incidence of pituitary tumours in males, mammary fibroadenomas in females, an increase in the incidence of severity of glomerulonephrosis, and a greater incidence of animals which died without any obvious pathology. It is concluded that, in our Sprague-Dawley substrains, both the individual and the group mean body weights in early adult life appear predictive for the individual and group life expectancy. The decrease in longevity in the CD-COBS-VAF rat is principally due to disease and degeneration processes associated with fast growth and high body weight.

Cardiotoxicity of hydralazine and minoxidil in the rat. Influence of age.

In this study, the cardiotoxicity of isoproterenol, hydralazine and minoxidil was compared between young (1.5 months old) and mature (5 months old) rats. Both age classes were also compared for the effect of hydralazine on blood pressure and heart rate. For the 3 compounds, myocardial necrosis was observed and was more marked in mature than in young rats. The age-related increase in sensitivity to cardiotoxic effects which has already been described for isoproterenol, can therefore be extended to hydralazine and minoxidil. Hydralazine produced hypotension and reflex tachycardia. This latter effect appeared to have a longer duration in mature animals, which may be one of the explanation for their increased sensitivity to the cardiotoxic effect of the compound.