No Clinically Significant Interaction Between Verzenio and Mebendazole
There is no documented drug interaction between Verzenio (abemaciclib) and mebendazole, and these medications can be used together without dose adjustment.
Pharmacologic Basis
The FDA label for Verzenio specifically addresses drug interactions and focuses exclusively on CYP3A inhibitors and inducers 1. Abemaciclib is metabolized primarily by CYP3A4, making it susceptible to interactions with strong/moderate CYP3A inhibitors (requiring dose reduction) and CYP3A inducers (which should be avoided) 1.
Mebendazole, however, does not significantly interact with the CYP3A system in a clinically meaningful way. A comprehensive pharmacokinetic review of mebendazole interactions identified interactions with:
- CYP inducers (phenytoin, carbamazepine, phenobarbital) - which decrease mebendazole levels
- Cimetidine - which increases mebendazole levels
- Ritonavir - which decreases mebendazole levels 2
Notably absent from this list is any interaction with CDK4/6 inhibitors or medications metabolized by CYP3A4.
Abemaciclib's Effect on Other Drugs
Research demonstrates that abemaciclib does not cause clinically meaningful drug-drug interactions as a perpetrator drug. Despite downregulating CYP mRNA in vitro (including CYP1A2, 2B6, 2C8, 2C9, 2D6, and 3A), clinical studies using a drug cocktail approach found no clinically relevant effects on substrates of CYP3A4, CYP2C9, CYP2D6, or CYP1A2 3. This indicates that abemaciclib is unlikely to alter the metabolism of concomitant medications through CYP pathways.
Clinical Monitoring Considerations
While the drugs can be co-administered, be aware of:
Abemaciclib's effect on serum creatinine: Abemaciclib inhibits renal tubular transporters (OCT2, MATE1, MATE2-K), causing reversible creatinine elevation without true renal injury 4. Approximately 50% of patients experience changes in renal function classification, with 22.6% requiring dose adjustments of other renally-excreted medications 4. This is a false elevation and should not be mistaken for actual kidney damage.
Mebendazole is typically short-term: Most anthelmintic therapy with mebendazole is brief (days to weeks), minimizing any theoretical interaction risk 2.
Bottom Line
Proceed with concurrent use without dose modification. Monitor for abemaciclib's known adverse effects (diarrhea 83.5%, neutropenia 45.8%, fatigue 40.6%) 5, but do not attribute these to mebendazole interaction. If creatinine rises during concurrent therapy, recognize this as an expected abemaciclib effect rather than true renal injury 4.