Determination of the antihypertensive drug 1-[2-ethoxy-2-(3′-pyridyl)ethyl]-4-(2′-methoxyphenyl)piperazine (IP/66) in rat and human plasma by high-performance liquid chromatography and isotope dilution mass spectrometry

Abstract

In connection with pharmacokinetic studies on the antihypertensive drug 1-[2-ethoxy-2-(3′-pyridyl)ethyl]-4-(2′-methoxyphenyl)piperazine (IP/66) (I), appropriate high-performance liquid chromatographic (HPLC) and gas chromatographic—mass spectrometric isotope dilution (GC—MS—ID) methods for its determination in rat and human plasma, respectively, were developed. In both techniques, deproteinized and basified plasma samples were extracted and purified by adsorption on an Extrelut-1 column, then the drug was eluted with dichloromethane. Quantitative HPLC analysis was performed on a C 8 reversed-phase column. The mobile phase was phosphate buffer (0.02 M, pH 2.8)—acetonitrile (65:35), with UV detection at 208 nm. The internal standard was 1-[2-butoxy-2-(3′-pyridyl)ethyl]-4-(2′-methoxyphenyl)piperazine, a homologue of I. The inter-assay coefficient of variation (C.V.) was 9.9% for a drug level of 2 μg/ml. Quantitative GC—MS—ID analysis was performed with a DB-17 fused-silica capillary column using the selected-ion monitoring technique. The deuterated form of I, 1-[2-ethoxy-2-(3′-pyridyl)ethyl]-4-2′-trideuteromethoxyphenyl)-piperazine, utilized as internal standard, was synthesized. The inter-assay C.V. was 7.36% for a drug level of 1 ng/ml.