Development of a low-dose monthly injectable contraceptive system: I. Choice of compounds, dose and administration route.

A low-dose combined estrogen-progestogen sustained release system has been developed. The control of crystal size of the steroids produced sustained dissolution in vitro and in vivo. A dose-response experiment carried out in healthy women indicated that 10 mg of norethisterone (NET) with 1 mg of ethinylestradiol (EE2) when given by intramuscular injection maintained NET serum levels above 1 ng/ml for at least 25 days. The system is considered suitable for one month contraceptive protection.