A Sensitive Isocratic Liquid Chromatography Assay for the Determination of Dipyridamole in Plasma with Electrochemical Detection

For many years, dipyridamole (DP) has been used in the treatment of hypertension as a vasodilatator, but recently it has been recognized as an anti-platelet aggregation agent and to potentiate cytotoxic. A rapid and very sensitive (1 nM) procedure for the determination of free and protein-bound DP in plasma, using reversed-phase high-performance liquid chromatography on a μBondapark C18 (10μm) column (300 × 3.9 mm I.D.) with coulometric detection (+ 0.65 V), is reported. Free and bound DP were separated using ultrafiltration. The liquid-liquid extraction from plasma included solvent extraction using diethyl-ether and a preparative column to separate DP from constituents normally found in plasma. The particular columns used contained a specially modified form of diatomaceous earth which requires no-preconditioning washes. The overall recovery from plasma was 52 ± 12 % at the concentration of 0.5 ng/ml (1 nM). Concentrations of DP between 1 nM and 1 μM were measured in plasma with relative standard deviations under 7.6 % (n = 6). The subsequent determination of DP levels in patients orally administered from 107 to 500 mg/m2/day showed that DP binding to plasma protein was higher than 90 % with a mean at 97.2 % (95.5 % to 92.3 %).