Drug levels and HIV

July 2001     View PDF     En español

Women and pharmacology

There are known and possible other considerations for women with regard to how drugs are processed in the body. Studies describing some of these considerations note sex differences in metabolism, drug levels and side effects.

One study that looked at differences in blood levels of the NNRTI drug, delavirdine (Rescriptor), in men and women showed that women who took delavirdine + AZT (Retrovir) had nearly twice the amount of delavirdine in their blood at trough levels than men, even though both took the same doses. Possible explanations for this difference include weight and body mass differences and hormones. Whatever the cause, the study suggests that women may absorb some drugs differently than men and that researchers should watch for this effect.

In addition to higher drug levels in blood, some studies report increased or varied side effects from anti-HIV drug use in women. A ritonavir study showed that women experienced more nausea, vomiting and malaise than men. Some women also experienced a unique and potentially dangerous side effect caused by ritonavir—excessive menstruation. While the cause of these differences remains unknown, it suggests that women and men might need different drug doses to lessen these effects.

Little research has taken place to evaluate different dosing schemes in women. It remains unknown if or how people might safely decrease their doses and maintain potency of a drug when faced with side effects. In the short-term, it’s probably unwise to simply decrease doses of anti-HIV drugs to manage side effects. Reduced dosing may result in fewer side effects, but it may also cause the drug to fail or HIV to develop resistance to it.

Drug interactions between anti-HIV therapy and other drugs commonly used by women are another important consideration. For instance, some protease inhibitors decrease estrogen among women on hormone replacement therapy (HRT) or oral contraceptives, while the protease inhibitor indinavir (Crixivan) and the NNRTI efavirenz (Sustiva) increase estrogen.

Practically speaking, women on protease inhibitors should be counseled on how to alter the dose of their oral contraceptives or HRT to maintain effectiveness and/or use other methods of birth control. Also, this suggests that some protease inhibitors might decrease the natural level of estrogen in women, leading to other health issues associated with low estrogen levels (like early menopause or loss of bone density).

As the field of HIV drug pharmacology becomes more complicated, many basic questions remain regarding differences in women. In order to answer them, it’s critical that sufficient numbers of women participate in studies of new therapies, as well as other studies that may reveal possible sex differences. Industry, government and community must work together to prioritize these research areas and to address the barriers that remain for women’s involvement in research.

Drug interactions

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