Biol. Pharm. Bull. 30(9) 1784—1786 (2007)

hibitors used to treat human immunodeficiency virus (HIV)1. Tenofovir can be administered once-daily at a dose of 300 mg in combination with other antiretroviral drugs. The advantage of once-daily dosing is a reduction in patient drug load. Also, tenofovir appeared to be well tolerated with low rates of drug-related therapy discontinuation in several clinical trials. Thus, tenofovir use is expected to increase. However, some drug interactions with tenofovir and coadministered drugs have been reported. Furthermore, tenofovir has been associated with renal impairment. Recently, several determination methods for plasma tenofovir using high-performance liquid chromatography (HPLC) or liquid chromatography-tandem mass spectrometry (LC-MS-MS), have been reported. HPLC methods, however, are procedurally complicated, such as solid-phase drug extraction and derivatization with chloroacetaldehyde. Also, when using the LC-MS-MS method the MS-MS detector needs to be delicately set. In addition, LCMS-MS equipment is very expensive. We aimed, therefore, to develop a conventional procedure for determining tenofovir using liquid chromatography coupled with mass spectrometry (LC-MS).