Development of radioimmunoassay for sultopride and sulpiride

Sensitive radioimmunoassays for both sultopride and sulpiride in human serum have been developed. The antiserum used was obtained by immunizing rabbits with sultopride albumin conjugate. Using tritiated sultopride as the ligand, a sensitive standard curve was established with a useful range from 0.05 to 5 ng. The antiserum showed less than 1% cross reactivity with sultopride metabolites but 4.5% with sulpiride, which enabled us to establish a sulpiride standard curve between 0.1 and 500 ng. Serum concentrations of sultopride or sulpiride after single oral administration to normal volunteers have been determined using these radioimmunoassays. Serum sultopride levels reached peak 1 hr after the administration and declined with an apparent half life of 3.5 hr, while serum sulpiride levels increased gradually and the high serum level at 2 hr remained for up to 6 hr. Such differences in sultopride and sulpiride pharmacokinetics may depend on their different lipid solubilities.