Gender May Play Important Role in Viramune (nevirapine) and Sustiva (efavirenz) Blood Levels

By Bonnie Darves

Gender differences may be the reason why women with HIV infection experience greater toxicity problems than do men when treated with nevirapine or efavirenz. Results of a new study on the issue, which has proved problematic for physicians treating women with HIV, were presented last week at the 4th International Workshop on Clinical Pharmacology of HIV Therapy in Cannes, France.

The study is important because the suspected gender differences in response to some antiretrovirals may have serious implications for both toxicity and long-term outcomes, said researchers from universities in Rotterdam and Groningen, The Netherlands. A better understanding of those gender differences could help treating physicians to develop more individualized drug dosing, according to lead researcher Charles la Porte, from University Medical Centre, in Nijmegen.

The retrospective study included data collected from therapeutic drug monitoring samples for nevirapine from 100 women and 268 men (mean age 35.5 years for women and 43.5 for men) treated during 2002. The study enrolled only patients who received the recommended nevirapine or efavirenz doses -- 200 mg twice daily and 600 mg once daily. Patients in whom non-compliance was suspected were excluded from the study.

The researchers found that levels of both nevirapine and efavirenz were higher in women than in men. Specifically, nevirapine levels were 6.7 mg/L in the women and 5.5 in the men. Efavirenz levels were 3.0 mg/L and 2.3, respectively, for the two groups.

Dr. La Porte said that no significant differences were seen between women and men in co-medication use, therapeutic drug monitoring indications, or time between last intake and reporting. As such, gender appeared to be the largest single predictive factor for toxic plasma levels -- which supports the recommendation that "physicians should be on the alert for increased toxicity risk in female patients," he said.

03/31/03

Source
Doctors Guide Dispatch. March 28, 2003.