Paliperidone Palmitate Long-Acting Injectable Given Intramuscularly in the Deltoid Versus the Gluteal Muscle: Are They Therapeutically Equivalent?

Paliperidone palmitate long-acting injectable is a second-generation antipsychotic indicated for the treatment of schizophrenia. According to the product monograph, the monthly maintenance dose of paliperidone palmitate can be given in either the deltoid or gluteal muscle. Unfortunately, many clinicians may misinterpret these directions to mean that these intramuscular sites are interchangeable, and thus therapeutically equivalent. Currently, the literature on this topic is sparse, but the published pharmacokinetic studies and Food and Drug Administration submission data on paliperidone palmitate show discrepancies in the elimination half-life, peak plasma concentration, and absorption rate that are dependent on the site of injection. The degree of shifts in pharmacokinetic parameters suggests that paliperidone palmitate injections via the deltoid and gluteal muscle are not bioequivalent and therefore are not therapeutically equivalent. Thus, using the same maintenance dosing regimen at both sites or switching between sites of injection may result in unforeseen consequences in patient outcomes.