Drug Interactions between Cycloset and letermovir

ADJUST DOSE: Coadministration with moderate inhibitors of CYP450 3A4 may significantly increase the plasma concentrations of bromocriptine. Orally administered bromocriptine is extensively metabolized in the gastrointestinal tract and liver by CYP450 3A4, with approximately 93% of the absorbed dose undergoing first-pass metabolism and only the remaining 7% reaching systemic circulation. As such, inhibitors of CYP450 3A4 may markedly reduce the metabolic clearance of bromocriptine. The interaction has been studied with erythromycin, a moderate CYP450 3A4 inhibitor. When a single 5 mg oral dose of bromocriptine was given following a 4-day treatment of erythromycin estolate 250 mg four times a day in five male volunteers, mean bromocriptine peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 4.6- and 3.7-fold, respectively, compared to administration of bromocriptine alone. High bromocriptine plasma levels may increase the frequency and/or severity of adverse effects such as nausea, headache, dizziness, somnolence (e.g., episodes of sudden sleep onset), hypotension, syncope, and impulse control problems or compulsive behaviors (e.g., gambling or sexual urges; uncontrolled spending).

MANAGEMENT: Caution and close monitoring for development of adverse effects are advisable during coadministration of bromocriptine with moderate CYP450 3A4 inhibitors. Bromocriptine dosage may need to be reduced to avoid toxicity. The prescribing information for Cycloset, a bromocriptine product indicated for use in adults with type 2 diabetes mellitus to improve glycemic control, recommends limiting the dose to 1.6 mg daily during concomitant use of a moderate CYP450 3A4 inhibitor.

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