What serious adverse reactions to ivermectin have been reported in children versus adults?
Executive summary
Clinical reports and reviews find serious adverse events from oral ivermectin are uncommon in children: systematic reviews of children <15 kg (1,088 kids) found 1.4% had adverse events and none were serious [1] [2]. In adults, pharmacovigilance and case-series link rare but severe neurological events (including encephalopathy and deaths) mainly to high Loa loa microfilarial loads, co‑infection or overdose, and to mass‑treatment programs in sub‑Saharan Africa [3] [4].
1. Children’s safety record: limited data, few serious events
Available pooled data on young children show mild, self‑limited reactions rather than life‑threatening events. An individual patient data meta‑analysis covering 1,088 children under 15 kg reported 18 adverse events in 15 children (1.4%) and explicitly found no serious adverse events in that dataset [1] [2]. A multicentric observational study of infants and small children treated for scabies likewise reported seven mild adverse events among 170 patients and no serious events [5]. These sources indicate published pediatric evidence to date documents mostly minor reactions for the studied indications, but they also acknowledge data are limited and that some regulatory labels still withhold approval under a weight cutoff because controlled pediatric studies are sparse [6] [7].
2. Adults: rare but documented severe neurological and fatal outcomes tied to context
In adults, pharmacovigilance studies and case series have identified rare but serious neurological adverse events, including encephalopathy and deaths, particularly where ivermectin was given to people heavily infected with Loa loa or in settings where drug interactions or genetic variants might permit central‑nervous‑system penetration. A review of serious neurological adverse events found case reports in international safety databases and discussed mechanisms such as co‑infection with Loa loa and MDR‑1 (P‑glycoprotein) gene variants that could allow ivermectin into the brain [3]. A systematic pharmacovigilance study found 667 suspected serious adverse drug reactions after ivermectin between 2003 and 2020, with 209 deaths among antinematodal agent reports; it stressed severe encephalopathies in patients with heavy Loa loa infections and uneven reporting across countries [4].
3. Mechanisms and risk factors that differentiate adults from children in reports
The literature links the most severe adult events to specific biological or programmatic risk factors: high Loa loa microfilarial loads (leading to post‑treatment encephalopathy), possible genetic mdr‑1 variants, drug–drug interactions, and overdoses from veterinary formulations or misuse [3] [4] [8]. For pediatric populations the main signals in the reviewed studies were mild reactions attributed to parasite killing (an inflammatory “Mazzotti”-type response) and not to encephalopathy; but authors note pediatric pharmacovigilance systems and databases often lack weight data, limiting detection of rare weight‑specific harms [1] [5] [9].
4. Common and serious reactions reported across age groups
Common, typically transient side effects listed by clinical resources include nausea, diarrhea, dizziness, swelling, pruritus, fever, rash, myalgia and headache — reactions that often relate to parasite die‑off and immune responses [10] [11]. Serious reactions reported in adults include severe skin reactions, liver injury and, most prominently in safety reviews, neurological events up to fatal encephalopathy in the context of Loa loa co‑infection or overdose [10] [4] [3]. For children, the cited systematic reviews and observational studies report only mild, self‑limiting events in the assembled cohorts [1] [5].
5. Data gaps, reporting biases and regulatory caution
Authors repeatedly emphasize limited data and reporting gaps: active surveillance databases often lack weight information so pediatric cases may be undercounted; reporting varies by country and mass‑treatment programs may both reveal and confound risk signals [1] [4]. Regulatory labels and drug information note that safety in children under 15 kg has not been fully established and that topical ivermectin has different pediatric labeling than oral forms [6] [12] [7]. These constraints mean absence of evidence of serious pediatric harm in published series does not equal proof of absence.
6. Practical takeaways and competing viewpoints
The conservative medical position reflected in product monographs and major clinics is to dose oral ivermectin by weight and to withhold or use caution below 15 kg because controlled pediatric data remain limited [6] [7]. Conversely, systematic reviews of published small‑child cases conclude existing limited data suggest safety and have called for reconsideration of the contraindication in some contexts [1] [2]. Public‑health signals in adults — serious neurological events linked to Loa loa and programmatic use — warn clinicians to screen travel/exposure history and avoid misuse or veterinary formulations [4] [8].
Limitations: available sources do not mention every specific adverse event a clinician might encounter; weight‑stratified pharmacovigilance is incomplete and surveillance biases exist [1] [4].