Effect of timiperone on 3H-spiroperidol binding to rat striatal dopamine receptors

Carbonyl reduction of timiperone in human liver cytosol

This in vitro study using human liver enzymes was undertaken in order to compare the mechanism of metabolic reduction of timiperone, a potent butyrophenone neuroleptic, with that of haloperidol. Conversion of timiperone to reduced timiperone in liver cytosol was confirmed. The carbonyl reductase inhibitors (menadione IC50 5-18 microM; ethacrynic acid IC50 26-51 microM) potently inhibited both timiperone reductase and haloperidol reductase activity, while 4-methylpyrazole (alcohol dehydrogenase inhibitor) had no effect and phenobarbital (aldehyde reductase inhibitor) had a weak inhibitory effect. The formation of reduced timiperone was highly correlated with the formation of reduced haloperidol(r = 0.87, n = 6, P < 0.02). Timiperone reductase activity was approximately 40% lower than haloperidol reductase activity (at a substrate concentration of 100 microM, two-tailed t-test, P < 0.05). The Michaelis-Menten constant (Km) and maximum velocity (Vmax) of reduced timiperone formation were much lower than reduced haloperidol formation (K(m) values: 29.7 +/- 15.1 versus 381.3 +/- 1.1 microM, n = 3, P < 0.01; Vmax: 0.81 +/- 0.19 versus 6.00 +/- 1.47 nmol/mg/min; n = 3, P < 0.05). However, the ratio Vmax/K(m) (clearance) for timiperone was 1.3-2.4 times higher than for haloperidol, indicating that metabolic clearance of timiperone by carbonyl reductase may be similar to or slightly higher than for haloperidol.

Plasma concentrations of timiperone and its reduced metabolite in the patients on timiperone

Plasma levels of timiperone (TIM) and reduced timiperone (RTIM) were determined in 10 schizophrenic patients who were treated with TIM. Activities of ketone reductase in red blood cells (RBC) were assayed using TIM and haloperidol (HAL) as substrates. Plasma levels of TIM and RTIM ranged from 3.2 ng/mL to 9.5 ng/mL and from 1.7 ng/mL to 7.6 ng/mL, respectively, and approximately four-fold inter-individual variations in RTIM/TIM (0.37-1.43, 0.67 +/- 0.25) were observed. There were significant and positive correlations between plasma levels of TIM or RTIM with the daily doses of TIM (mg/kg body weight); TIM (ng/mL)= 19.5 x daily dose of TIM (mg/kg) + 1.3, r = 0.79, n = 18, P < 0.01; RTIM (ng/mL) = 13.1 x daily dose of TIM (mg/kg) + 0.7, r = 0.73, n = 18, P < 0.001). Given 0.3 mg/kg of TIM, a plasma level of TIM as 7.15 ng/mL was predicted, which is approximately 60% that of HAL. The activity of TIM reductase in RBC was determined as approximately 70% of HAL reductase in RBC, although the correlation between the activities of TIM reductase and HAL reductase in RBC was high (r = 0.98, n = 10, P < 0.001).

Disposition of timiperone, 4'-fluoro-4-[4-(2-thioxo-1-benzimidazolinyl)piperidino]butyrophenone, a neuroleptic, in the rat on repeated oral dosage

1. The metabolic disposition of [14C]timiperone was studied in male Wistar strain rats receiving an oral dose of 0.5 mg/kg consecutively daily for 21 days. 2. Blood concentrations of 14C indicate that absorption of [14C]timiperone on repeated dosage may be similar to that after a single dose. 3. Tissue levels of 14C after repeated doses were increased to up to double those after a single dose, but the decline of tissue concentrations after the 21st dose was similar to that after a single dose. Thus, no rat tissue show accumulation. 4. Repeated administration did not affect the metabolism of timiperone. 5. Excretion of 14C on the third day of repeated medication was urine, 44.7% and faeces 52.4% of the cumulative dose, and total daily excretions were more than approx. 97% of the cumulative dose in days 3-21 of the repeat dosage schedule.