Induction of microsomal enzyme activity by flupenthixol in chronic schizophrenics

The effect of long-term treatment with flupenthixol on hepatic microsomal enzyme activity was studied in 12 chronic schizophrenic outpatients who had been receiving two weekly maintenance doses for at least 6 months. Antipyrine half-life was measured in the 12 patients while they continued to receive the drug. Flupenthixol was then discontinued for 6 weeks and antipyrine half-life was repeated in 7 of the 12 patients. In the 12 patients the plasma antipyrine elimination half-life was 4-24 h (mean 9.73 +/- 1.61 h) when receiving flupenthixol and there was a significant negative correlation between antipyrine half-life and the dose of flupenthixol (r = 0.582, P less than 0.05). In the seven patients to whom antipyrine was given on two occasions, antipyrine half-life was 7.33 +/- 1.07 h and 12.04 +/- 1.87 h on and off flupenthixol treatment respectively. The clearance significantly decreased when flupenthixol was discontinued, but there was no change in the apparent volume of distribution.