Effect of esomeprazole on pharmacokinetics of phenytoin in rabbits

Esomeprazole is commonly prescribed proton pump inhibitor for gastritis and peptic ulcer disease. Most of the time in clinical practice, phenytoin and esomeprazole are prescribed for patients of generalized seizures with concomitant peptic ulcer. Hence there are chances of drug-drug interaction because of modulations of isoenzymes CYP2C9 and CYP2C19, are involved in metabolism of phenytoin and esomeprazole. But it is important to maintain the therapeutic level of phenytoin in plasma for effective seizures control. So, the aim of the study was to determine the effect of esomeprazole on the pharmacokinetics of phenytoin in rabbits. In a parallel design study, phenytoin, 30 mg/kg/day per oral was given daily for 14 days. On day 15, blood samples were taken at various time intervals between 0-24 hours. In esomeprazole-phenytoin group, phenytoin was administered for seven days as mentioned earlier and from day 8th onward, esomeprazole 2.8 mg/kg along with phenytoin 30 mg/kg/day was administered till 14th days and blood samples were drawn as above on 15th day. Plasma phenytoin levels were assayed by HPLC and pharmacokinetic parameters were calculated. In esomeprazole-phenytoin group, there was a significant increase of t1/2el than phenytoin alone group and significant increase in AUC0-24 was also observed in the esomeprazole and phenytoin treated group. These results suggest that esomeprazole alters the pharmacokinetics of phenytoin. Confirmation of these results in further clinical studies will warrant changes in phenytoin dose or frequency when esomeprazole is co-administered.