Does ivermectin interact with ribociclib?

Drug Interaction Between Ivermectin and Ribociclib

Yes, ivermectin and ribociclib have a clinically significant drug interaction that requires careful consideration and likely avoidance of concurrent use.

Mechanism of Interaction

Ribociclib is a moderate-to-strong CYP3A4 inhibitor 1. The FDA label clearly demonstrates that ribociclib increases exposure to CYP3A4 substrates substantially—specifically, it increases midazolam (a sensitive CYP3A4 substrate) exposure by 3.8-fold for AUC and 2.1-fold for Cmax at the 400 mg dose, with even greater effects predicted at 600 mg (5.2-fold and 2.4-fold increases respectively) 1.

Ivermectin is metabolized primarily by CYP3A4 2. When ivermectin is co-administered with CYP3A4 inhibitors, its plasma concentrations increase significantly. The acne vulgaris guidelines specifically list ivermectin among drugs that interact with macrolide antibiotics (which are CYP3A4 inhibitors) 2.

Clinical Significance

The combination would be expected to substantially increase ivermectin plasma levels, potentially leading to toxicity. Ivermectin toxicity can manifest as:

• Central nervous system effects (dizziness, ataxia, seizures—particularly concerning as ivermectin can cross the blood-brain barrier) 3
• Increased risk of adverse effects in vulnerable populations

Recommendation

Avoid concurrent use of ivermectin and ribociclib. If parasitic treatment is absolutely necessary in a patient receiving ribociclib:

1. Consider alternative antiparasitic agents that are not CYP3A4 substrates
2. If ivermectin is unavoidable, consider:
   • Temporary interruption of ribociclib (discuss with oncology team regarding cancer treatment implications)
   • Close monitoring for ivermectin toxicity if co-administration cannot be avoided
   • Awareness that standard ivermectin doses may produce supra-therapeutic levels

Important Caveats

• Ribociclib's inhibitory effect on CYP3A4 is dose-dependent and time-dependent 1
• The interaction would be present regardless of whether ribociclib is dosed at 400 mg (early breast cancer) or 600 mg (advanced breast cancer), though the magnitude may differ
• Recent research confirms ribociclib significantly impacts CYP3A4 substrate metabolism even at the lower 400 mg dose 4
• This interaction is not explicitly listed in ribociclib's FDA label, but the mechanism is clear based on the known metabolic pathways

Bottom line: This is a predictable pharmacokinetic interaction that warrants avoidance of concurrent use to prevent ivermectin toxicity.