[A method to quantify diazepam with high resolution liquid chromatography in patients undergoing multiple therapy].

A rapid, sensitive and specific method useful in monitoring diazepam in patients receiving multiple therapy is presented. Plasma was extracted in the presence of borate buffer with hexane and the drug was quantified by HPLC in a Novapak C 18 column. The limit of detection in plasma was about 30 ng/mL. Analytical recovery of the drug added to plasma was about 70%. Within-day variation and between-day variation ranged from 5.9 to 8.3 and 5.9 to 10.7%, respectively. The method was applied in the determination of diazepam levels in patients treated with this drug in combination with other drugs commonly used in our hospital. The concentrations found in most of the patients were in the therapeutic range. It was not possible to detect the drug in one patient with concomitant administration of magnesium hydroxide, which can be attributed to a reduced absorption of diazepam in presence of the antiacid. Average steady-state concentrations of diazepam in psychiatric patients, submitted to 5 mg doses t.i.d. during four weeks, were in the range of 200 to 450 ng/mL.