Efavirenz Treatment and False‐Positive Results in Benzodiazepine Screening Tests
Departments of 1Internal Medicine VI, Clinical Pharmacology and Pharmacoepidemiology, and 2Dermatology, University Hospital Heidelberg, Heidelberg, and 3Schwerpunktpraxis Mannheim, Mannheim, Germany
We investigated the effect of efavirenz treatment on the results of drug screening tests of urine samples obtained from 100 patients infected with human immunodeficiency virus. Of 50 patients who received efavirenz, 49 tested positive for benzodiazepines in
1 drug screening test, whereas of 50 patients who did not receive efavirenz, only 1 tested positive for benzodiazepines in
1 drug screening test. The major metabolite 8‐hydroxy‐efavirenz is responsible for this cross‐reactivity.
Received 11 December 2008; accepted 29 January 2009; electronically published 11 May 2009.

