Detection and determination of total amlodipine by high-performance thin-layer chromatography: a useful technique for pharmacokinetic studies.

A novel analytical method for determination of the total plasma levels (free and protein bound) of the calcium channel blocking agent amlodipine has been developed using a high-performance thin-layer chromatographic (HPTLC) procedure. Detection and quantitation were performed without internal standards. In previously described methods for the estimation of amlodipine by gas chromatography and high-performance liquid chromatography, only the free levels in plasma and serum were quantified at 7% of the total amlodipine level, with the remaining 93% bound to plasma protein and tissue. The present method employs proteolysis of the plasma proteins by incubating plasma for 2 h in pepsin solution. After proteolysis amlodipine is extracted and a known amount of the extract is spotted on precoated silica-gel 60 F254 plates using a Camag Linomat IV autosampler. Amlodipine was quantified using a dual-wavelength TLC scanner. The method provides a direct estimate of the total amlodipine present in plasma.