What drug‑drug interactions should be considered when taking ivermectin?

Drug-Drug Interactions with Ivermectin

Azithromycin significantly increases serum ivermectin concentrations and should be used with caution when co-administered, while warfarin may require INR monitoring due to rare reports of increased INR. 1, 2

Critical Pharmacokinetic Interactions

CYP3A4 Enzyme Interactions

Ivermectin is primarily metabolized by cytochrome P450 3A4 (and to a lesser extent 3A5 and 2C9), making it susceptible to interactions with drugs that induce or inhibit this enzyme system 3:

• Strong CYP3A4 inhibitors (e.g., ketoconazole, azole antifungals) can increase ivermectin exposure, potentially enhancing both efficacy and toxicity risk 4
• CYP3A4 inducers (e.g., rifampin, rifabutin, anticonvulsants, corticosteroids) may decrease ivermectin levels and reduce therapeutic efficacy 1, 3
• Anticonvulsants and steroids specifically induce ivermectin metabolism, potentially requiring dose adjustments 1

P-Glycoprotein (P-gp) Transporter Interactions

Ivermectin is a substrate for P-glycoprotein, which normally limits its penetration into the central nervous system 3, 5, 6:

• P-gp inhibitors can increase brain concentrations of ivermectin, potentially causing severe neurotoxicity 6
• Co-administration with drugs that inhibit P-gp (including some antiretrovirals, calcium channel blockers, and certain antifungals) may elevate CNS toxicity risk 3, 6
• Genetic polymorphisms in P-glycoprotein can also predispose patients to increased neurotoxicity 5, 6

Specific Drug Interactions

Documented Interactions

• Warfarin: Post-marketing reports indicate rare cases of increased INR when co-administered; monitor INR closely if combination is necessary 2
• Azithromycin: Significantly increases serum ivermectin concentrations; use with caution and consider dose reduction 1

Food Interactions

• High-fat meals increase ivermectin bioavailability by 2.5 times 1
• Ivermectin should be taken on an empty stomach with water to ensure consistent absorption 1, 2
• When enhanced absorption is desired (e.g., for systemic parasitic infections), taking with food may be beneficial 5

Clinical Monitoring Recommendations

Hepatic Function Considerations

• Use caution in patients with reduced hepatic function, as ivermectin metabolism may be impaired 1
• Avoid combination with other hepatotoxic medications (azole antifungals, certain antiretrovirals, high-dose acetaminophen) in patients with liver disease 7

Alcohol

• Warn patients that alcohol is reported to worsen side effects of ivermectin 1

Special Populations at Higher Risk

Patients with Loa loa Co-infection

• In patients with significant Loa loa exposure (West or Central Africa), pretreatment assessment and careful post-treatment follow-up are essential, as severe or fatal encephalopathy can occur 2
• This risk may be exacerbated by drugs that inhibit P-glycoprotein 6

Elderly Patients

• Treatment should be cautious due to greater frequency of decreased hepatic, renal, or cardiac function and concomitant medications 2

Common Pitfalls to Avoid

• Do not assume ivermectin is free of interactions simply because it is generally well-tolerated; CYP3A4 and P-gp interactions are clinically significant 3, 6
• Do not co-administer with strong P-gp inhibitors without considering increased neurotoxicity risk, particularly in patients with genetic polymorphisms 6
• Do not ignore the timing of food intake, as this substantially affects bioavailability 1, 5
• Always review the complete medication list before prescribing, including over-the-counter medications, supplements, and herbal remedies that may affect CYP3A4 or P-gp 1