Enzyme induction by moricizine: time course and extent in healthy subjects

Moricizine.HCl, a novel phenothiazine derivative with oral antiarrhythmic activity, was examined for its potential to induce its own hepatic metabolism and to alter the pharmacokinetics of the test substrate, antipyrine, in 12 healthy male subjects. Antipyrine oral clearance increased from a starting value of .74 mL/minute/kg to .98 (+32%, P < .01) after 7 days of moricizine administration (250 mg every 8 hours) and to 1.15 mL/minute/kg after 14 days (+47%, P < .05); t1/2 was correspondingly reduced. Moricizine oral clearance increased from a baseline of 3.01 L/hour/kg to 3.62 (+20%, P < .05) after 6 days of oral moricizine and 4.66 (+51%, not significant) after 13 days. Moricizine t1/2 was marginally, but consistently, increased (+23%, P < .05) instead of decreased as one would expect because of enzyme induction, presumably due to a decrease in systemic bioavailability and its influence on the oral volume of distribution. In half of the subjects who discontinued moricizine after 7 days, antipyrine pharmacokinetic values returned to near baseline 7 days later. Although moricizine was able to induce its own hepatic metabolism and that of antipyrine after 6 or 7 days of continuous administration, the electrocardiographic properties of moricizine did not appear to be altered by continuous dosing.
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