What are the clinical signs and timeline of ivermectin overdose in adults and children?
Executive summary
Ivermectin overdose in humans most commonly produces gastrointestinal upset, circulatory instability and a range of neurological symptoms that can progress from lethargy and confusion to seizures, coma and rarely death; onset can be within hours but some neurotoxic effects may evolve over days [1] [2] [3]. Children follow largely the same spectrum of toxicity as adults, but safety for those under 15 kg is not established and dosing must be weight‑based, which complicates overdose risk assessment in small children [4] [5] [6].
1. Early signs — stomach, skin and mild neurologic disturbance
The first complaints after excessive ivermectin exposure are typically gastrointestinal — nausea, vomiting and diarrhea — often accompanied by non‑specific complaints such as headache, dizziness, pruritus or mild tremor; these are the earliest documented manifestations in public‑health advisories and poison‑control reports [1] [2] [3]. Dermatologic reactions can also appear and, while usually minor, pharmacovigilance data link ivermectin to rare but serious skin reactions including Stevens‑Johnson syndrome, toxic epidermal necrolysis and DRESS, which clinicians should consider when rashes accompany systemic signs [7].
2. The neurologic spectrum — from sleepiness to seizures and coma
Neurologic toxicity ranges from somnolence, gait imbalance, confusion and visual disturbances to frank seizures, depressed consciousness and coma; authoritative case series and clinical reviews note that serious neurological events—abasia, tremor, loss of consciousness and coma—have occurred after overdose or in special circumstances where blood‑brain barrier protection is compromised [8] [3] [7]. Although ivermectin is normally excluded from the human brain by P‑glycoprotein pumps, mutations in the ABCB1 gene or coexisting conditions that weaken the blood‑brain barrier appear to permit CNS penetration and explain severe neurotoxicity in some patients [3] [8].
3. Timeline — hours to days, with possible delayed progression
Signs can appear within hours of a large ingestion — animal and veterinary reports document central‑nervous‑system signs developing within 5–48 hours — and human case reports and advisories likewise describe early onset GI and neurologic symptoms, with some neurologic deterioration occurring over days rather than instantaneously [9] [10] [1] [2]. The variability in onset reflects dose, formulation (human versus highly concentrated veterinary preparations), individual susceptibility (including transporter mutations), and whether other CNS‑depressant drugs are present; clinicians therefore monitor exposed patients for an extended period even if initial signs are mild [11] [3] [12].
4. Differences in children and dosing‑related risks
Therapeutic dosing is weight‑based (commonly ~150–200 mcg/kg as a single oral dose), and labels and drug guides emphasize that safety in children under 15 kg has not been established, making accidental overdose in small children a particular concern when adult‑formulation or veterinary products are used [4] [5] [6]. Reported pediatric toxicity follows the adult pattern — GI symptoms and neurologic depression — but because young children have smaller margins between therapeutic and harmful doses and dosing errors are more likely, conservative management and rapid consultation with poison control or emergency specialists is recommended [4] [12].
5. Severity, treatment and limits of the evidence
Life‑threatening poisoning is rare but documented, with hypotension, seizures, respiratory depression and death reported in surveillance and public‑health advisories; treatment is primarily supportive — airway, breathing, circulation, symptomatic care, and consideration of activated charcoal if presentation is early — and there is no routinely available antidote [2] [12] [3]. Crucially, the literature has limits: many serious ADRs are rare, some case series involve co‑morbid infections (confounding symptoms), and there is sparse controlled data on human overdose thresholds, so much guidance derives from pharmacovigilance, case reports and veterinary experience rather than large human overdose trials [8] [7] [12].
6. Context and caveats — misuse, veterinary products and public narratives
Public health agencies and poison centers have repeatedly warned that misuse of ivermectin for unapproved indications and ingestion of veterinary formulations has driven many recent toxicity reports, a point that colors both clinical caseloads and media narratives and may inflate perceptions of risk tied to very high‑concentration animal products [1] [2] [11]. At the same time, regulatory and pharmacovigilance studies affirm that therapeutic ivermectin, when correctly dosed, is generally well tolerated — the debate is not over whether ivermectin can be used safely in approved indications but over preventing misuse and recognizing rare but serious idiosyncratic or overdose‑related events [4] [8] [7].