Investigation of InterferenCe by Nonsteroidal Anti-Inflammatory Drugs in Urine Tests for Abused Drugs

Anecdotal and uncontrolled studies have suggested that nonsteroidal anti-inflammatory drugs produce false-positive resuits in immunoassay urine tests for some drugs of abuse. This study was performed in 60 volunteers who took ibu-profen as either a single 400-mg dose, or 200 mg three times a day, or 400 mg three times a day, and in 42 patients taking ibuprofen, naproxyn, or fenoprofen in therapeutic regimens for more than 30 days. Of the 510 urines collected from 102 individuals during these dosage regimens, two gave false-positive tests for cannabinoid by enzyme-mediated immu-noassay (EMIA), one after 1200 mg of ibuprofen in three divided doses for one day and one in a patient taking naproxyn on a chronic basis; none was falsely positive for benzodiazepines. Two unnes were false-positive for barbitu-rates by fluorescence polarization immunoassay (FPIA), on