Concomitant use of any of the following drugs: isoniazid, iproniazid, dantrolene, ticrynafen (tienilic acid), ibufenac, bromfenac, benoxaprofen, zileutan, nicotinic acid, trovafloxacin, perhexiline, dilevavol, labetalol, pemoline, felbamate, tolcapone, diclofenac, AIDS drugs (HIV+ subjects are excluded anyway), and troglitozone.