Plasma concentrations of thiothixene and clinical response in treatment-resistant schizophrenics

Plasma concentrations of thiothixene were measured during treatment of 42 treatment-resistant schizophrenic patients. Inter-individual variability was marked even when patients were treated with the same dose or dose regimen. Intra-individual variability was less but still considerable. A highly significant correlation was found between dose and plasma concentration, but this relationship was unpredictable for individual patients. A median plasma concentration of 12 to 15 ng/ml might be expected with daily doses of 60 mg. No definite range of therapeutic plasma concentrations could be determined. Patients who attained moderate degrees of improvement did so at a median dose of 26 ng/ml, which is within the range of therapeutic plasma concentrations previously reported for thiothixene in similar patients.