Biological efficacy and plasma norethisterone levels of orally administered norethisterone enanthate in rat and hamster.

Norethisterone enanthate (NET-En) is a well known intramuscular contraceptive drug. The long acting nature of this preparation when administered orally was evaluated in female rats and hamsters using fertility inhibition test and from the plasma levels of norethisterone (NET). An oral dose of 20-60 mg NET-En was administered to random groups of six female rats and hamsters and were mated after five and ten days with males of proven fertility. The fertility inhibition rate was determined from vaginal delivery. A dose-dependent reduction in fertility was seen in rats 5 days after oral administration of NET-En. This effect was found to be less pronounced and not significant 10 days after administration of similar doses of NET-En. In hamsters, a similar but less pronounced effect was noted. The decrease in fertility was significant only at the 60 mg dose. The plasma levels of NET estimated by RIA over a period of 15 days, in a different set of treated rats, suggested rapid absorption of NET-En within a day, and drug concentration decreased slowly, the levels on the 4th day ranged from 0.9-2.3 with the 10 mg and 1.0-4.0 ng/ml with the 20 mg dose. Detection of adequate levels of NET in plasma during the estrous cycle in rats, and the fertility inhibition observed in female rats and at higher doses in hamsters, suggest that NET-En is orally active.

Interferencia endometrial de los estrógenos sintéticos en la regulación de la fertilidad / Endometrial interference of synthesis estrogens in fertility regulation

Inicialmente la actividad antiovulatoria de algunos preparados estrógeno/progestacional, era la acción requerida para controlar la fertilidad. A la fecha se ha conseguido una notable reducción en la dosis de ambos componentes hormonales, ofreciendo menos efectos colaterales, con una eficacia anticonceptiva aceptable. Actualmente se dispone de una variedad de esas combinaciones, en donde el estrógeno sintético concentra de 80 a 20 µg/tableta y la prescripción se inicia o el 1er. día o el 5o. día del ciclo menstrual. Al analizar el plasma y el endometrio simultáneamente obtenida de usuarias crónicas que incluían en la tableta dosis de 30 o 50 µg del estrógeno sintético, se observó un perfil de 17B-estradiol como el de la maduración folicular de los ciclos ovulatorios sólo en las mujeres que tomaban la dosis más baja. Sin embargo, este fenómeno de ciclicidad no se obtuvo a nivel local; paralelamente la progesterona circulante en ambos grupos nunca fue > 5.0 ng/ml. La observación indica que se debe buscar un periodo crítico local durante el ciclo menstrual ovulatorio, con mucho menores dosis hormonales para controlar la fertilidad