Convenience and compliance are 2 important factors in assuring a desired therapeutic outcome with any treatment. Although >16 million women in the United States use some form of oral contraceptive, the rate of unintended pregnancy among users during the first year of therapy is still 5%. Intolerance of oral therapy, inability to follow treatment guidelines, and the need to ensure prolonged infertility are just a few reasons why the sustained effectiveness demonstrated by injections of medroxyprogesterone is considered important.
The World Health Organization (WHO) and the International Planned Parenthood Federation encourage the use of this progestin-based, long-acting contraceptive among populations where access to oral contraception is limited. FDA approval for the contraceptive use of medroxyprogesterone was granted in the United States in the 1990s.
Medroxyprogesterone is a derivative of progesterone. When administered every 3 months, it inhibits the natural secretion of gonadotropins, thereby preventing maturation of the ovarian follicles. This causes thinning of the endometrium, which in turn produces a contraceptive effect. Compared to oral agents, its use results in a pregnancy rate ranging from 0 to 0.7% during the first year of use. Although the drug is indicated for the prevention of pregnancy, it has also been used in unique cases of court-mandated chemical castration in confirmed male sex offenders.
Administration and Dosing
The recommended dose of medroxyprogesterone acetate suspension is 150 mg, administered every 3 months (or 13 weeks) by deep intramuscular injection to the gluteal or deltoid muscle. The suspension should be vigorously shaken just before use to guarantee uniform dosage.
To ensure that medroxyprogesterone is not inadvertently administered during a pregnancy, the first injection must be given only (1) during the first 5 days of a normal menstrual period, (2) within the first 5 days postpartum if not breast-feeding, or (3) if exclusively breastfeeding, at the sixth postpartum week. If the time interval between injections exceeds 13 weeks, pregnancy testing should be conducted before drug administration.
Results of a prospective study released in 2004 indicate that medroxyprogesterone can cause loss of bone mineral density in first-time users. Although this loss may be reversed when the injections are discontinued, the long-term impact on peak bone density among adolescent users should be strongly considered when initiating birth control with medroxyprogesterone.
A weight gain of between 5 and 8 pounds is generally seen following the first 2 years of medroxyprogesterone use as birth control, increasing to an average of 16.5 pounds after 6 years. In a long-term trial using medroxyprogesterone, 2% of participants dropped out of the study due to weight gain. Since the formulation has a prolonged duration of action, a return to fertility takes an average of 10 months (time range of 4 to 31 months) after medroxyprogesterone has been discontinued.
In addition to suspected pregnancy, specific contraindications to medroxyprogesterone use include atypical vaginal bleeding, suspected breast malignancy, liver dysfunction, and presence or history of thrombophlebitis. Therapy should be discontinued in the event of sudden changes in, or loss of, vision. Patients also need to be reminded that birth control does not afford protection from sexually transmitted diseases.
In light of recent adverse effects associated with estrogen-based treatments, the desire for ease of compliance and guaranteed effectiveness has brought the focus of contraception to progestin-based therapies.
Medroxyprogesterone provides highly effective contraception with a prolonged duration of activity. It has been used worldwide for many years with the endorsement of WHO and is gaining favor in the United States when other birth control methods prove inadequate. Medroxyprogesterone is manufactured as a sterile suspension, in prefilled syringes of 150 mg, by Teva Pharmaceutical Industries Ltd and Greenstone Ltd.