Lack of a pharmacokinetic drug-drug interaction between lithium and valproate when co-administered with aripiprazole

What is known and Objective: The antipsychotic, aripiprazole, plus lithium or valproate demonstrates rapid and significant improvement in manic symptoms that is sustained over the long term. A previous report showed that therapeutic doses of either lithium or valproate had no clinically significant effects on the pharmacokinetics of aripiprazole. We aimed to determine the effects of co‐administration of aripiprazole on the steady‐state pharmacokinetics of lithium or valproate in healthy subjects. Materials and Methods: Two similarly designed, open‐label, single‐sequence studies were conducted. Healthy subjects received daily oral doses of either lithium (450 mg every 12 h) or valproate (500 mg every 12 h) on Days 1–7. Following Day 7 was a 2‐day washout period, and on Day 10, subjects began receiving oral doses of aripiprazole (10 mg once daily) for 2 days. Aripiprazole was then titrated from 10 to 20 mg once daily to establish tolerance of aripiprazole. On Day 14, the dose was escalated and subjects received aripiprazole 30 mg once daily for 13 days. Beginning on Day 20, subjects received lithium (450 mg every 12 h) or valproate (500 mg every 12 h) concomitantly with aripiprazole 30 mg once daily through Day 26. Serial blood samples for serum lithium or valproate concentration determination were collected for up to 12 h post‐lithium or valproate administration on Days 7 and 26. Results: The lithium study enrolled 32 healthy subjects (72% completed the study), and the valproate study enrolled 48 healthy subjects (58% completed the study). In both studies, the 90% confidence intervals for the ratios of population geometric means, with and without aripiprazole, were contained within 80% and 125% for both the C_max and AUC_τ, respectively. Furthermore, the addition of aripiprazole did not change the median T_max of lithium or valproate (4 h). Thus, the addition of aripiprazole did not affect the steady‐state pharmacokinetics of lithium or valproate. The majority of subjects (76·9% for aripiprazole plus lithium and 68·4% for aripiprazole plus valproate) reported adverse events, but this adverse event profile is consistent with what has been observed in other studies. What is new and Conclusion: The addition of aripiprazole to either lithium or valproate had no clinically meaningful effects on the pharmacokinetics of either drug. In addition, co‐administration of aripiprazole with lithium or valproate demonstrated no unexpected safety signals in healthy subjects.