DETERMINATION OF APOMORPHINE IN HUMAN PLASMA BY ALUMINA EXTRACTION AND HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

Apomorphine is a powerful agonist of dopaminergic receptors which seve ral years ago was introduced into the therapy of Parkinson's Disease. The pharmacological activity of apomorphine already appears significan t at low doses. Unfortunately, the difficulty in determining the drug in plasma at low concentrations hampers the completion of accurate pha rmacokinetic studies in humans. Considering the analogy of apomorphine with the molecular structure of catecholamines, the extraction of the drug from plasma was optimized by using adsorption on alumina, a tech nique widely used for noradrenaline and adrenaline analysis in clinica l chemistry laboratories. This method proved particularly efficient an d selective in apomorphine extraction from plasma prior to high-perfor mance liquid chromatographic analysis. After pretreatment of 200 mu l of plasma sample with 40 mg of alumina and 10 mu l of tris buffer (pH 8.6), the drug was eluted with 200 mu l of an acidic-organic solution. One volume of the supernatant was mixed with two volumes of phosphate buffer (pH 3.6), and 100 mu l of the obtained mixture were injected i nto the HPLC system. The chromatograph was equipped with a C18 reverse d-phase column and with an electrochemical coulometric detector fitted with a high-sensitivity cell (first electrode 0.00 volts, second elec trode +0.35 volts). Sensitivity (20 pg of injected drug), precision (C V within assay and between assays of 3.7% and 5.6%, respectively) and accuracy were comparable to more complex analytical procedures. The mi niaturisation of the entire sample pretreatment proved very advantageo us for pharmacokinetics studies and, ih principle, for therapeutic dru g monitoring and toxicological investigations. (C) 1997 Elsevier Scien ce Ireland Ltd.