Combination of Olanzapine and Samidorphan Has No Clinically Significant Effect on the Pharmacokinetics of Lithium or Valproate.

BACKGROUND AND

OBJECTIVE

Olanzapine is an atypical antipsychotic indicated for the treatment of schizophrenia and, either as monotherapy or as an adjunct to lithium or valproate, for bipolar I disorder. Multiple daily doses of olanzapine do not affect the pharmacokinetics of lithium or valproate; therefore, concomitant olanzapine administration does not require dosage adjustment of lithium or valproate. ALKS 3831, a combination of olanzapine and the opioid receptor antagonist samidorphan (OLZ/SAM), is currently under development to provide the established antipsychotic efficacy of olanzapine while mitigating olanzapine-induced weight gain. Olanzapine is recognized as one of the most efficacious antipsychotics; however, the benefits of olanzapine are offset by its propensity to cause significant weight gain, which may lead to long-term metabolic sequelae. This study evaluated the effects of multiple daily doses of OLZ/SAM on the pharmacokinetics of lithium or valproate in healthy subjects.

METHODS

This was an open-label, single-sequence, two-cohort study (ALKS3831-B101) conducted at a single center in the USA. Thirty-four healthy adult subjects were assigned (1:1) to receive lithium carbonate 300-mg tablets (cohort 1) or divalproex sodium 500-mg tablets (cohort 2), once every 12 h on days 1-7. Once-daily oral doses of OLZ/SAM (olanzapine 10 mg/samidorphan 10 mg) bilayer tablets were administered on days 8-18. Subjects resumed every 12-h doses of lithium or valproate concomitantly with the once-daily oral doses of OLZ/SAM on days 12-18. Plasma concentrations of lithium and valproic acid (valproate) were quantified in blood samples collected prior to and up to 12 h after lithium or valproate dose administration on days 7 and 18. Pharmacokinetic parameters of lithium and valproate, including maximum plasma concentration and area under the plasma concentration-time curve over a 12-h dosing interval, were calculated. The ratio of geometric means of maximum plasma concentration and area under the plasma concentration-time curve over a 12-h dosing interval in the presence and absence of OLZ/SAM, and its two-sided 90% confidence intervals, were derived from a mixed-effects model. Adverse events were monitored throughout the study.

RESULTS

The 90% confidence intervals for the ratios of geometric means, in the presence vs. absence of OLZ/SAM, were within the equivalence interval of 80-125% for both maximum plasma concentration and area under the plasma concentration-time curve over a 12-h dosing interval of lithium and of valproate. The safety profiles of lithium or valproate co-administered with OLZ/SAM were consistent with what has been previously reported for lithium or valproate. The safety profile of OLZ/SAM was consistent with that observed in previous clinical studies with OLZ/SAM.

CONCLUSIONS

Consistent with previously reported findings on olanzapine, administration of multiple doses of OLZ/SAM did not have a clinically significant effect on the pharmacokinetics of lithium or valproate. Co-administration of OLZ/SAM and lithium or valproate was generally well tolerated; the safety profile of OLZ/SAM was consistent with that observed in previous clinical studies.