Injectable depot contraceptives on d-norgestrel basis. I. Pharmacokinetic studies in dog and baboons

Effect of two new androgen esters on serum levels of testosterone in castrated rhesus monkey

The pharmacokinetics of two new androgen esters were tested in castrated male rhesus monkeys. A single injection of 40 mg of 20 Aet-2 (testosterone-trans-4-n-pentyl cyclohexyl carboxylate) increased serum testosterone to three times the castrate levels and was maintained nearly at this level until day 182. When given as four separate injections of 20 mg each, 20 Aet-2 increased serum testosterone within 24 hours and the peak levels were attained on day 2 (34.6 +/- 6.20 nmol/L) which was more than five times the levels obtained by 40 mg 20 Aet-2 given as a single injection. This was followed by a decrease in serum testosterone until day 98 when the levels were similar to that in animals given a single injection of 20 Aet-2. Administration of 40 mg of 3 Ad (testosterone-cis-3-(n-hexyl) cyclobutane carboxylate) given as a single injection increased serum testosterone levels to reach a peak level (47.4 +/- 4.64 nmol/L) on day 5 followed by a gradual decrease to castrate levels by day 70. The profile of serum testosterone in animals injected with 80 mg of 3 Ad as four separate injections was similar to that in animals given a single dose of 40 mg of 3 Ad. The data suggest a correlation between the bioavailability of the drug and the formulation of the vehicle. The possible effect of hydrolysis rate on pharmacokinetics of the drugs is discussed.

Pharmacokinetics of levonorgestrel in the rat

Levonorgestrel was administered intravenously as a bolus to adult female rats and blood samples were collected at various time intervals. Serum concentrations of levonorgestrel were measured by radioimmunoassay. Analysis of data for two- and three-compartment open models indicated that in the rat, as in the human and the rabbit, a tri-exponential equation provided a better fit of the data. The half-lives for the alpha, beta and gamma phases were 10.1 min, 42.7 min and 23.1 hours, respectively. These values were closer to those reported for women than were the half-lives reported for the rabbit. The alpha and the beta phases appeared to last for 51 min and 1.3 hours, respectively, and the gamma phase was longer than 45 hours.

Long-acting contraceptive agents: structure activity relationships in a series of norethisterone and levonorgestrel esters

A large number of esters of norethisterone (17 alpha-ethynyl-17 beta-hydroxyestr-4-en-3-one) and levonorgestrel (D-(-)-13 beta-ethyl-17 alpha-ethynyl-17 beta-hydroxygon-4-en-3-one) were synthesized and tested for biological activity. The test employed in these studies was the duration of estrus suppression in cycling mature rats. In the norethisterone series several esters exhibited duration of activity comparable to that of norethisterone enanthate. In the levonorgestrel series the butanoic, cyclobutylcarboxylic and cyclopropylcarboxylic esters were longer acting than medroxyprogesterone acetate (17 alpha-acetoxy-6 alpha-methylpregn-4-ene-3,20-dione) when prepared as aqueous microcrystalline suspensions.

Treatment of rhesus monkeys (Macaca mulatta) with intravaginal rings impregnated with either progesterone or norethisterone

The effects of both progesterone- and norethisterone-loaded intravaginal rings were investigated in twenty-five rhesus monkeys for 52 weeks. The intravaginal rings were designed to provide a sustained release of either the human dosage level of the hormone or ten times this level. Untreated placebo rings were used for control purposes. The devices were well retained. With the exception of increased plasma fibrinogen levels in animals treated with norethisterone, no marked differences in either local or systemic toxicity between the progesterone and norethisterone intravaginal rings were apparent. Following insertion of the hormone-treated intravaginal rings, a dose-related decrease in vaginal bleeding was recorded. The vaginal microbial flora were assessed qualitatively and semiquantitatively and all groups including the placebo controls showed a changes in mcirobial populations. Terminal studies indicated that at high dose levels, ovulation was suppressed and widespread atrophy of the uterine mucosal and glandular endometrial epithelium had occurred. An increase in cervical mucus was observed within the lumen of the endocervical canal in a proportion of hormone-treated animals. In the vagina, a dose-related focal or diffuse atrophy of the mucosal epithelium was found.

A new principle of injectable depot contraceptives. I Drug selection and studies in monkeys

The aim of the investigations was to develop a long-acting depot contraceptive on the basis of norethisterone or levonorgestrel. Disappointing results with levonorgestrel nonanoate and levonorgestrel undecylate showed that elongation of the fatty acid, esterified with the steroid, decreased the bioavailability of the latter due to incomplete hydrolysis of the ester. Therefore, several new compounds were synthesized which contained a bifunctional molecule between the steroid and the fatty acid. In vivo studies showed an increase in hydrolysis when glycolic acid was taken as the "bridge", compared to the hitherto known esters. Due to the new principle of the steroid-fatty acid connection, in the case of norethisterone, it was possible to introduce tridecanoic acid as lipophilic release controlling substituent without a loss of bioavailability in the baboon. This compound (called: "norethisterone glycotridecanoate") and the corresponding levonorgestral derivative were chosen for a pharmacokinetic-clinical study in women.