Pharmacokinetics of omeprazole in rats with water deprivation for 72 hours.

Dehydration can occur by excessive sweating, polyuria, severe diarrhea and hyperthermia. Previous studies reported that the expressions of CYP1A1/2 and 3A1(23)/2 were not changed in male Sprague-Dawley rats with 72 h water deprivation (dehydrated rats), and that the metabolism of omeprazole is mainly catalysed via CYP1A1/2, 2D1 and 3A23/2 in rats. Hence, it could be expected that the hepatic metabolism of omeprazole would not be changed considerably in dehydrated rats, if the contribution of CYP2D1 to the metabolism of omeprazole in dehydrated rats is not considerable. Therefore, the pharmacokinetics of omeprazole were compared after intravenous (20 mg/kg) and oral (40 mg/kg) administration in control rats and in dehydrated rats. After intravenous administration, the time-averaged nonrenal clearance (Cl(nr)) values of omeprazole were comparable between the two groups of rats. This could be supported by comparable in vitro intrinsic clearance (Cl(int)) values for the disappearance of omeprazole in rat hepatic microsomes and the comparable free (unbound to plasma proteins) fractions of omeprazole in plasma in the two groups of rats. After oral administration, the AUC values of omeprazole were also comparable in the two groups of rats. The above data suggest that the dehydration state did not affect considerably the pharmacokinetics of omeprazole in rats.