Mechanism of action and pharmacokinetics

The most important mechanism whereby DMPA protects against unwanted pregnancy is the inhibition of ovulation. The mid-cycle surge of gonadotropins is eliminated. Estrogen levels in the peripheral circulation of DMPA acceptors are within the range usually found in the early follicular phase of a normal menstrual cycle. Additional antifertility effects include the formation of an atrophic endometrium and a thick, viscous cervical mucus, which impedes sperm penetration. Fallopian tube motility may also be decreased.

Based on studies that measured gonadotropin levels in DMPA users, ovulation is suppressed for at least 14 weeks following each intramuscular injection and 15 weeks following subcutaneous injection of DMPA. Following either a single dose or multiple tri-monthly injections of 150 mg DMPA, the levels of medroxyprogesterone acetate (MPA) in the peripheral circulation increase and reach peak concentrations at approximately 8–10 days following the last injection. The serum concentrations of DMPA then gradually decline for the remainder of the 12-week dosing interval. Depending on the sensitivity of the assay, MPA may be found in the serum more than 200 days following a single injection of 150 mg DMPA. Repeat injections of intramuscular DMPA at 12-week intervals do not result in an accumulation of drug as determined by the assay of MPA at frequent intervals. Recovery of the reproductive axis and pregnancy is quite variable from patient to patient. Pregnancy may occur as early as 4 months after the last DMPA injection and as late as 31 months or longer after stopping DMPA in order to conceive. The return of fertility is unrelated to the number of DMPA injections the patient has received.

Candidates for use

Depot medroxyprogesterone acetate is a contraceptive modality which is particularly suited for women who desire a long-acting, coitus-independent, convenient, highly efficacious method of family planning. Women who have medical conditions in which estrogen is contraindicated and who desire very effective contraception may wish to consider the use of DMPA, as it does not increase liver globulin production of angiotensin or clotting factors. For women with sickle cell disease, DMPA is the contraceptive method of first choice as it decreases blood loss and acute sickle cell crises. Another group of women who are especially suited to using DMPA as their contraceptive method are those with seizure disorders as it has been correlated with decreased seizure activity. Additionally, anticonvulsant medications should not interfere with the efficacy of DMPA, as they do with some other methods of hormonal contraception. DMPA is also used to treat endometriosis and may improve other conditions such as dysmenorrhea and anemia. For women who choose not to reveal their contraceptive choice to others, DMPA is ideal as it is not visible or palpable, nor does it require the patient to store the medication. It is also particularly well suited for teens and is associated with significantly fewer repeat teen pregnancies at 1 year than oral contraceptives or nonhormonal methods.

There are some women who should not receive DMPA. Current breast cancer is an absolute contraindication to DMPA. DMPA should be used with caution if there is no acceptable alternative for patients with: past breast cancer with no disease for 5 years; undiagnosed abnormal vaginal bleeding; a current pulmonary embolus or deep vein thrombosis; breastfeeding less than 6 weeks post partum; blood pressure 160/100; vascular disease; history of stroke or ischemic heart disease; migraine headaches with aura; diabetes with retinopathy, neuropathy, nephropathy, other vascular disease or more than 20 years of disease duration; multiple risk factors for coronary artery disease; active viral hepatitis; decompensated cirrhosis; hepatoma or benign hepatic adenoma. Patients must be advised that DMPA does not protect against sexually transmitted infections (STIs). DMPA users who are at risk for STIs should also use barrier methods for STI prevention. It should also not be used for women who wish to become pregnant within a year as only 50% of women who desire fertility after DMPA are pregnant by 6–10 months after the last injection. Women who are unable to return to the clinic every 3 months who desire effective, reversible, long-acting contraception should consider using the implant or an intrauterine device.

Initiating DMPA use

Depot medroxyprogesterone acetate is a long-acting, highly convenient family planning method which is easy to administer. It is an aqueous suspension of microcrystals administered by injection every 12 weeks. While women must currently return to a clinic for reinjection every 11–13 weeks, women could theoretically be taught to give themselves subcutaneous DMPA at home, thus eliminating the need to return to the clinic. The injection site should not be massaged immediately following each injection as this disperses the steroid and shortens its time of effectiveness.

A woman who has been consistently using another method of hormonal contraception may switch over to DMPA at any time. Women undergoing elective termination of pregnancy may be given DMPA prior to being discharged from the clinic. Postpartum women may also receive DMPA prior to hospital discharge.