SENSITIVE DETERMINATION OF FREE AND PLASMA PROTEIN-BOUND DIPYRIDAMOLE BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

For many years dipyridamole (DP) has been used in the treatment of hypertension as a vasodilator, but recently it has been recognised as an anti-platelet aggregation agent and to potentiate anti-metabolite activity. A rapid and sensitive (20 nM) procedure for the determination of free and protein-bound DP in plasma, using reversed-phase high-performance liquid chromatography on an Ultrasphere XL ODS (3-mu-m) column (70 mm x 4.6 mm I.D.) with ultraviolet detection (280 nm), is reported. Free and bound DP were separated using ultrafiltration. Concentrations of DP between 0.1 and 10-mu-M were measured in plasma with a relative standard deviation of < 9.6%. The subsequent determination of DP levels in patients orally administered 450 mg per day showed that DP binding to plasma protein is higher than 90%.