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Women and Pharmacology

March 2001

There are known and potential considerations for women with regard to how drugs are processed in the body, a field of study called pharmacology. Studies describing some of these note sex differences in metabolism, drug levels, and/or side effects. This article highlights some important observations for women living with HIV.


Delavirdine Study

Project Inform has previously reported on a study that looked at differences in blood levels of the NNTRI drug, delavirdine (Rescriptor) in men and women. As with almost all drugs, the amount of delavirdine in the blood rises to a high or peak level after taking the drug and then gradually declines to a trough or lowest level just before taking the next dose. But this study showed that women who took delavirdine (Rescriptor) + AZT (Retrovir) had nearly twice the amount of delavirdine (1.8 times more) in their blood at trough levels than men, even though both were taking exactly the same doses.

Potential explanations for this difference include weight and body mass differences and hormonal influences. Whatever the cause, the study suggests that women may absorb drugs differently than men in some cases and that researchers should be careful to watch for this effect.


Ritonavir Study

In addition to higher drug levels in blood, some studies have reported increased or varied side effects associated with anti-HIV drug use in women. A study looking at ritonavir (Norvir) 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, like the delavirdine study, it also suggests that women and men might need different dosage levels of drugs to lessen these effects. Little research has taken place to evaluate different dosing schemes in women, and it remains unknown if or how people might safely decrease doses and maintain potency and durability of a drug when faced with side effect concerns. In the short-term, it's probably unwise to simply decrease doses of anti-HIV drugs to manage side effects. Reduced dosing might result in lower side effects, but it may also cause the drug to fail or the virus to develop resistance to it.

Therapeutic drug monitoring, a testing process that may tell people the actual blood levels of the drugs they are taking, is currently being evaluated and may shed light in these areas. While still in the research phase, it's important that women seek out and participate in studies that include this new technology so that more information is gleaned that includes the experiences of women.


Drug Interactions

Drug interactions between anti-HIV therapies and other drugs commonly used by women are another important pharmacologic consideration. For instance, it is known that some protease inhibitors decrease the level of estrogen among women receiving hormone replacement or oral contraceptives, whereas the protease inhibitor indinavir (Crixivan) and the NNRTI efavirenz (Sustiva) increases the level of estrogen.

Practically speaking, women on protease inhibitors should be counseled on how to alter the dose of their oral contraceptives or hormone replacement therapy to maintain effectiveness and/or use alternative methods of birth control. Additionally, this also suggests that some protease inhibitors might decrease the natural level of estrogen in women, leading to other potential health considerations associated with low estrogen levels (such as early menopause and/or loss of bone density).


Commentary

As the field of HIV drug pharmacology becomes more complicated, many basic questions remain regarding differences in women. In order to answer these questions, it is critical that sufficient numbers of women participate in studies of new therapies, as well as other studies that may reveal potential gender 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.


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