Are there documented human cases of parenteral ivermectin administration and their outcomes?
Executive summary
Documented human cases of parenteral (typically subcutaneous) ivermectin administration exist, almost exclusively as emergency, off‑label use of veterinary formulations to treat life‑threatening Strongyloides hyperinfection or disseminated strongyloidiasis when oral absorption is impossible; many reports describe clinical improvement but serious neurological toxicity and drug accumulation have also been recorded [1] [2] [3]. Regulatory and pharmacology reviews emphasize that parenteral ivermectin is not approved for humans, oral delivery is the licensed route, and parenteral use remains a rescue option supported only by case reports and small series [4] [5].
1. Documented cases: what the medical literature reports
Multiple peer‑reviewed case reports and small case series describe humans receiving subcutaneous or other parenteral ivermectin—usually a veterinary preparation—most often for Strongyloides stercoralis hyperinfection in immunosuppressed patients who had paralytic ileus or could not absorb oral medication; these reports include successful clinical responses and measured serum drug concentrations [1] [2] [3] [5]. Specific publications include a 2005 Clin Infect Dis. case report of a 23‑year‑old with disseminated strongyloidiasis treated with subcutaneous ivermectin (200 μg/kg daily) and other reports of successful rescue therapy in transplant and critically ill patients [1] [2] [6].
2. Outcomes: successes and harms described in the reports
Outcomes in the published cases range from clinical cure or stabilization after parenteral dosing to markedly adverse events; some series report therapeutic serum concentrations and parasite clearance, while at least one review links drug accumulation after parenteral therapy (>40 ng/mL) to encephalopathy, demonstrating that neurological toxicity is a documented risk [3]. Broader surveillance and case series outside the hyperinfection context also document neurological adverse events after ivermectin exposure (confusion, ataxia, seizures), underscoring that even when parenteral therapy can save a life, it carries measurable danger—especially in critically ill or polypharmacy patients [7] [8].
3. Pharmacology and why parenteral use was tried
Pharmacokinetic analyses show that when enteral absorption is impaired, subcutaneous or other parenteral administration can raise and sustain plasma ivermectin levels that are antiparasitic, and case reports measured serum concentrations consistent with efficacy after parenteral dosing (e.g., rising to several ng/mL and sustained levels after repeated subcutaneous injections) [9] [1]. At the same time, ivermectin is highly protein bound and metabolized by hepatic CYP enzymes; hypoalbuminemia, impaired clearance, drug–drug interactions (e.g., CYP3A4 or P‑glycoprotein inhibitors), and critical illness can alter distribution and increase CNS penetration—mechanisms invoked to explain observed encephalopathy [5] [7].
4. Regulatory status, practice implications, and hidden agendas
No parenteral ivermectin product is approved for human use; published cases used veterinary formulations as a last‑resort, off‑label intervention under compassionate or emergency circumstances, a fact repeatedly emphasized in the literature and product monographs [10] [5]. This creates an implicit tension: clinicians faced with fatal disseminated strongyloidiasis may resort to veterinary formulations, and case reports naturally highlight successes—potentially biasing visibility—while systematic safety data are lacking, leaving regulatory guidance and liability concerns unresolved [10] [3].
5. Balanced takeaway and limits of the evidence
The medical record documents that parenteral ivermectin has been used in humans and can be lifesaving for Strongyloides hyperinfection when oral drug delivery is impossible, but the evidence base is limited to case reports and small series, parenteral formulations are not licensed for people, and serious neurological toxicity with drug accumulation has been reported; therefore parenteral use remains an emergency, last‑resort measure rather than an established therapy [1] [3] [4]. Available sources do not provide randomized or large observational data to define safety margins, dosing standards, or long‑term outcomes for parenteral human use, so conclusions must be confined to the documented case literature [3] [2].