Pharmacokinetics of cephalexin in dogs and cats after oral, subcutaneous and intramuscular administration.

A three-way crossover study was carried out in 10 dogs and nine cats to establish the pharmacokinetic parameters of the semi-synthetic cephalosporin antibiotic, cephalexin sodium, when administered orally, subcutaneously or intramuscularly. Ten dogs received a subcutaneous or intramuscular injection of 10 mg/kg bodyweight cephalexin or an oral dose of three 50 mg cephalexin tablets; the peak serum concentrations achieved were 24.9, 31.9 and 18.6 micrograms/ml, respectively, and the times taken to reach these peak levels were 1.2, 0.9 and 1.8 hours. Nine cats received either a subcutaneous or intramuscular dose of 0.25 ml cephalexin suspension (approximately 20 mg/kg bodyweight) or an oral dose of one 50 mg tablet; the peak serum concentrations achieved were 54.0, 61.8 and 18.7 micrograms/ml for the subcutaneous, intramuscular and oral administrations respectively, with times to peak concentrations of 1.1, 0.7 and 2.6 hours.

Spermatogenesis in the grey squirrel (Sciurus carolinensis) and changes during sexual regression.

In the testes of sexually active grey squirrels 8 stages of spermatogenesis were recognized each with a characteristic association of germ cells. The low numbers of spermatozoa in squirrel testes are the result of fewer spermatogonial divisions compared with those of most other mammals as well as a low efficiency of spermatogenesis, with only 42% of the germ cells becoming spermatozoa. A period of testicular regression which may be prolonged follows the breeding season in June/July. In fully regressed testes no stages of spermatogenesis could be recognized, the lumen of the seminiferous tubules was occluded and no stages later than primary spermatocytes were seen.

Progesterone concentrations in peripheral plasma of non-pregnant and pregnant grey squirrels (Sciurus carolinensis).

Plasma concentrations of progesterone in non-pregnant female grey squirrels were never greater than 3.2 nmol/l and no significant differences were found between levels in anoestrous, pro-oestrous and oestrous animals. During pregnancy, plasma concentrations of progesterone increased significantly and reached a maximum level of 318 nmol/l at around day 35 of the 44 day period of gestation. After parturition, plasma concentrations of progesterone fell sharply. The corpora lutea of pregnancy began to regress in size at about day 30 of gestation, before the maximum levels of progesterone in the plasma were reached, which suggests that there is an extra-ovarian source of progesterone. Chromatography of pregnancy plasma extracts showed that no significant amount of 5 alpha- or 5 beta-pregnane-3,20-dione was present and that progesterone accounted for 90% of the assay-positive material in pregnancy plasma from grey squirrels.