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April 06, 2004

ARVs and Depo-Provera

In addition to OCs, might some antiretroviral drugs such as Nevirapine affect the effectiveness of Depo-Provera, the injectable contraceptive?

Probably not enough to affect contraceptive effectiveness appreciably, although Nevirapine may lower the blood levels of the contraceptive progestin in Depo-Provera somewhat. Again data are sparse, but Nevirapine lowered the blood level of the progestin norethindrone in women taking a single dose of an oral contraceptives by 18% in one study. By extension, it is reasonable to expect Nevirapine to modestly lower the blood levels of Depo-Provera's progestin, MPA, as well.

However the dose of Depo-Provera is high enough so that it gives a good margin of effectiveness. For example WHO conducted a large comparison of 100mg versus the usual 150 mg dose. The lower dose still had excellent effectiveness. So a modest drop in MPA blood levels is unlikely to reduce effectiveness appreciably. Accordingly, WHO has classified progestin injectables for women on ARVs as Category 2 (Generally use, though special care may be needed.)

If there is a vulnerability of effectiveness it is likely to be at the end of the 3-month period when the blood levels of MPA begin to trail off. So although Depo-Provera re-injection can normally be given as much as 2 weeks late, for a woman on Nevirapine, striving to provide the next injection by the end of 3 months appears prudent.

Still, it really would be useful to have more evidence.

References:
WHO. A multicentred phase III comparative trial of Depot-Medroxyprogesterone Acetate given three-monthly at doses of 100mg or 150mg: 1. Contraceptive efficacy and side effects. Contraception. 1986;34:223-35.

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The "Pearls" offer answers to commonly asked questions about family planning. These "Pearls" are prepared by Dr. James D. Shelton, Senior Medical Scientist, Office of Population, United States Agency for International Development (USAID)

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