PHARMACOKINETICS OF DEPOT MEDROXYPROGESTERONE ACETATE CONTRACEPTION

Depot medroxyprogesterone acetate (DMPA) is ail aqueous suspension of 17-acetoxy 6-methyl progestin administered by intramuscular injection for long-term contraception. This highly effective injectable formulat ion of medroxyprogesterone acetate (MPA) has a prolonged duration of a ction since the progestin is released slowly from the muscle. MPA is d etected in the serum within 30 minutes after an injection of 150 mg. S erum concentrations vary between individual women but generally platea u at about 1.0 ng/mL for about three months, after which there is a gr adual decline. In some women, MPA can be detected in the serum for as long as nine months after a single injection of 150 mg. The circulatin g MPA initially inhibits the midcycle leutinizing hormone (LH) peak, b ut LH and follicle stimulating hormone (FSH) levels remain in the rang e of those for the luteal phase of a pretreatment control cycle. Since ovulation is inhibited, serum progesterone levels remain low (< 0.4 n g/mL) for several months following an injection of DMPA. When MPA leve ls fall below 0.1 ng/mL, ovulation resumes. Thus, return to fertility is delayed for several months if a woman wishes to conceive after rece iving one or move injections of DMPA. Following an injection of DMPA, serum estradiol levels initially are in the early to midfollicular pha se range (mean approximately 50 pg/nL). Serum estradiol levels begin t o rise about four months after a single injection when MPA levels fall below 0.5 ng/mL. For women who have used DMPA for several years, seru m estradiol levels range between 10 and 92 pg/mL, with mean levels of about 40 pg/mL. Despite these low levels of estradiol, hot flushes are a rare event, and the vaginal epithelium remains moist and well rugat ed. Women using DMPA for several years do not observe a change in brea st size. DMPA causes the endometrium to become atrophic, with small, s traight endometrial glands and decidualized stroma. The cervical mucus remains thick and viscid. DMPA is a very effective form of contracept ion because of its multiple mechanisms of action and slow release into the circulation.