The pharmacokinetics of sulpiride was studied in 6 healthy volunteers after intravenous and oral (tablets) administration of 100 mg. An open two- and in two subjects a three-compartment model was applied following intravenous administration. The average total distribution volume during the terminal slope was 2.72 +/- 0.66 l/kg and total systemic clearance was 415 +/- 84 ml/min. The serum half-life of the terminal slope following intravenous administration averaged 5.3 h (range 3.7--7.1 h) according to the two-compartment model. In two subjects the half-lives were 11.0 and 13.9 h when the three-compartment model was applied. Determinations of urinary excretion rates of unchanged sulpiride indicated a half-life of 7.15 h. Following intravenous administration, 70 +/- 9% of the dose was recovered unchanged in urine within 36 h; the mean renal clearance was 310 +/- 91 ml/min. Sulpiride was absorbed slowly, with peak concentrations appearing between 3 and 6 h after oral administration. The recovery of unchanged drug in urine following oral administration was 15 +/- 5% of the dose, with a mean renal clearance of 223 +/- 47 ml/min. The bioavailability determined from combined plasma and urine data was only 27 +/- 9%. The low bioavailability was probably due to incomplete absorption.

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Schizophrenic patients were treated with fixed doses of sulpiride (800 mg) or chlorpromazine (400 mg) during eight weeks using a double-blind design. In order to examine relationships between pharmacokinetic, clinical and biochemical parameters in relation to treatment the following variables were recorded before and 1, 2, 4 and 8 weeks after treatment. Concentrations of sulpiride, CPZ, 7-OH-CPZ, nor,-CPZ were determined in serum and CSF using liquid chromatography and mass fragmentography. Clinical variables were psychotic morbidity and side effects as evaluated by CPRS, NOSIE and side effect ratings. Monoaminergic variables were concentrations of the major cerebral monoamine metabolites, HVA, 5-HIAA and MOPEG in the cerebrospinal fluid as measured by mass fragmentography. Prolactin levels in serum and CSF were measured by radioimmunoassay.During steady state, concentrations of sulpiride in serum varied fourfold between patients and CPZ twentyfold. Drug concentrations in serum and CSF were highly correlated in CPZ-but not in sulpiride-treated patients. Although sulpiride passed into the CSF, transport between serum and CSF was restricted. In the sulpiride group, improvement of psychotic morbidity and HVA elevation in CSF tended to be negatively related to the drug concentrations in serum. Sulpiride-treated patients with extrapyramidal side effects had significantly higher drug concentrations in serum.In CPZ-treated patients, improvement of psychotic morbidity, HVA elevation and prolactin elevation all tended to be positively correlated to drug concentrations in serum and CSF. CPZ-treated patients with extrapyramidal side effects also had significantly higher CPZ concentrations in serum.In both treatment groups, the MOPEG reduction in CSF tended to be correlated to improvement of psychotic morbidity.The study supplied clinical evidence for the view that antipsychotic drugs belonging to the phenothiazine and benzamide series induce antipsychotic effects in schizophrenic patients in a graded fashion which is proportional to the degree of interaction with the central dopaminergic mechanisms. The results also support the view that sulpiride has a more selective effect on central dopaminergic mechanisms than chlorpromazine.In the schizophrenic patients studied and with the doses used, sulpiride concentrations tended to be maximal with regard to clinical and biochemical effects. For CPZ on the other hand, drug concentrations in some patients seemed to be too low to induce optimal effects.

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