New long-acting injectable microcapsule contraceptive system

• Published in: American journal of obstetrics and gynecology Vol. 135; no. 3; p. 419
• Main Authors: Beck, L R, Cowsar, D R, Lewis, D H, Gibson, J W, Flowers, Jr, C E
• Format: Journal Article
• Language: English
• Published: United States 01.10.1979
• Subjects: Animals; Capsules; Delayed-Action Preparations; Female; Haplorhini; Injections, Intramuscular; Lactates; Methods; Microspheres; Norethindrone - administration & dosage; Norethindrone - blood; Papio; Polymers; Time Factors; Progestational Hormones; Progesterone > analysis; Contraceptive Agents, Progestin > administraction and dosage; Contraceptive Agents > administraction and dosage; Estrogens > analysis; Norethindrone > administraction and dosage; Biology; Contraception; Hormones; Family Planning; Research Methodology; Contraceptive Agents, Progestin > analysis; Endocrine System; Contraceptive Agents, Female > administraction and dosage; Clinical Research; Contraceptive Methods; Contraceptive Agents, Female > analysis; Contraceptive Agents > analysis; Injectables; Physiology; Norethindrone > analysis; Animals, Laboratory
• ISSN: 0002-9378; 1097-6868
• DOI: 10.1016/0002-9378(79)90717-8

A new long-acting, injectable contraceptive which provides continuous controlled release of the steroid norethisterone (NET) for a precise period of 6 months following a single intramuscular injection is described. The prototype system consists of microcapsules made of the biodegradable polymer d, l-polylactic acid, in which micronized crystals of NET are homogeneously dispersed. NET is slowly released from the microcapsules following intramuscular injection at a rate of 0.90 microgram NET/day/mg of microcapsule by diffusion of the steroid from the polymer matrix. Three different doses of a standard preparation of microcapsules were tested in normally cycling female babbons (4 to 5 baboons/group). Following injection of either 300, 200, or 100 mg of microcapsules containing 75, 50, or 25 mg of NET, blood samples were collected at selected intervals and analyzed for NET, estrogen, and progesterone by radioimmunoassay. All three doses provided continuous NET release for 6 months following injection. The NET serum profiles for the different doses are parallel, and ovulation was inhibited in all baboons for 6 months following treatment.