Melphalan estimation by quantitative thin-layer chromatography. Observations on melphalan hydrolysis in vitro and pharmacokinetics in rabbits.

A simple and specific quantitative high-performance thin-layer chromatographic (HPTLC) assay for melphalan in plasma is described. This assay was linear over the investigated range of 50--3,000 ng/ml, with a minimum level of detection of 20 ng/ml. Comparison with a high-pressure liquid chromatographic (HPLC) technique yielded similar estimates for melphalan concentrations in human plasma samples. The HPTLC method, unlike the HPLC technique, does not resolve monohydroxymelphalan satisfactorily. The HPTLC method was used to determine the activation energy for in vitro melphalan hydrolysis: this was 14.5 kcal/mole. The pharmacokinetics of melphalan in rabbits were also investigated. The mean t1/2 in four animals was 32.6 +/- 10.3 (S.D.) min and following IV administration to two animals the apparent volumes of distribution were 2.20 and 1.73 l/kg.