What are the potential side effects of ivermectin?

Ivermectin Side Effects

Ivermectin is generally well-tolerated at approved doses for parasitic infections, with the most common side effects being dizziness, nausea, fever, headache, muscle or joint pain, and skin reactions, while serious adverse events are rare. 1

Common Side Effects

When used at standard dosing (200-250 μg/kg) for approved parasitic infections, patients typically experience mild and transient symptoms: 2

• Dizziness, nausea, fever, headache, and muscle/joint pain are the most frequently reported side effects 1
• Skin reactions including rash, urticaria, and contact dermatitis may occur 3
• Gastrointestinal symptoms such as vomiting, diarrhea, and abdominal pain are common 3
• These effects are generally mild and self-limited, requiring no specific intervention 4

Mazzotti Reaction (Onchocerciasis-Specific)

When treating onchocerciasis, patients may develop a Mazzotti reaction due to microfilarial death, characterized by: 1

• Tender lymphadenopathy, headache, bone/joint pain, fever, urticaria, and asthma 1
• Severe reactions occur in approximately 9% of patients after initial treatment but decrease significantly with subsequent doses (18% after second dose, 11% after third dose) 5
• All severe adverse reactions appear within 48 hours of the first dose 5
• Side effects requiring therapy occurred in 32% after first dose but diminished to 18% and 11% after subsequent treatments 5

Serious Adverse Events (Rare)

Serious complications are uncommon but include: 3

• Encephalopathy (rare, primarily in patients heavily co-infected with Loa loa): confusion, lethargy, stupor, seizures, or coma 3
• Hepatotoxicity: cytolysis and elevated liver enzymes have been reported 6
• Cardiac effects: sinus tachycardia and cardiac dysfunction 6
• Neurological symptoms: ataxia, tremors, seizures, and paresthesia (typically only with overdose or veterinary formulation exposure) 3

Special Populations at Higher Risk

Patients with severe liver disease may be at increased risk for toxicity, as safety in this population is not well-established 1, 2

Elderly patients warrant particular caution due to greater frequency of decreased hepatic, renal, or cardiac function 3, 6

Patients with Loa loa co-infection require pretreatment assessment and careful post-treatment monitoring due to risk of fatal encephalopathy 3

Management of Adverse Effects

• Topical reactions can be relieved with topical corticosteroids and oral antihistamines 1
• Severe reactions in onchocerciasis may require pretreatment with corticosteroids in high-risk patients 1
• First-time treatment should occur under strict medical supervision for at least 48 hours given that severe reactions occur within this timeframe 5

Important Dosing Considerations

• Take on an empty stomach with water, as bioavailability increases 2.5-fold with high-fat food 1, 3
• Standard dosing for parasitic infections is 200-250 μg/kg 2
• Overdose symptoms (at 25-50 mg/kg in animal studies) include ataxia, tremors, decreased activity, and mydriasis 3

COVID-19 Context

In COVID-19 studies, moderate certainty evidence suggests ivermectin may increase the risk of serious adverse events in hospitalized patients (RR 3.10,95% CI 0.54-17.89), though the evidence remains imprecise 7. The WHO strongly recommends against ivermectin for COVID-19 outside clinical trials, noting it diverts resources from proven therapies 7.