Challenges for switching central nervous system and psychiatric medication products: A review of the literature.

Background: Switching between versions of medication products happens commonly despite challenges in achieving bioequivalence and therapeutic equivalence. Central nervous system and psychiatric drugs, especially those that are technically demanding to manufacture and have complex pharmacokinetic properties, such as long-acting injectables (LAIs), pose particular challenges to bioequivalence and safe and efficacious drug switching.

Aims: To assess whether drugs deemed "bioequivalent" are truly interchangeable in drug switching.

Methods: We assessed the published literature from January 2017 through June 2023 on PubMed using the MeSH terms "drugs, generic" OR "equivalency, generic" combined with terms for different psychiatric drug classes.

Results: While most of the published studies returned in the search found that switching drug products was safe and clinically comparable, data on most drug classes other than those primarily indicated in the treatment of seizure disorder were sparse. Some studies also provided evidence that real-world outcomes such as adherence and hospitalizations may also be affected by switching. In addition, a review of bioequivalence testing guidance showed inconsistency across agencies and a lack of product-specific guidance from Health Canada, which raises questions about potential claims of bioequivalence for more complex products such as LAIs.

Conclusions: Overall, given the difficulty in treating mental health disorders, prescribers should be cautious when switching products and formulations in a patient who has been stabilized on a drug.