What human safety data exist for subcutaneous or intramuscular ivermectin formulations intended for injection?
Executive summary
Human safety data for subcutaneous (SC) or intramuscular (IM) ivermectin intended for injection are extremely limited: a handful of case reports and small pharmacokinetic observations describe compassionate use of veterinary SC formulations in life‑threatening strongyloidiasis, while formal clinical trials of injectable ivermectin in humans do not exist and the FDA has not approved any parenteral product for people [1] [2].
1. What evidence exists from human case reports and clinical practice
Published case reports document successful rescue therapy with subcutaneous veterinary ivermectin in patients with disseminated or hyperinfective Strongyloides stercoralis who could not absorb oral drug due to ileus, showing clinical responses and measurable rises in serum ivermectin after SC dosing; these reports emphasize that such use is exceptional, requires regulatory permission (investigational new drug, IND), and is based on limited numbers rather than controlled safety trials [1] [2] [3].
2. Pharmacokinetic signals from human observations
Small human observations indicate that SC administration can produce higher or more sustained plasma concentrations than failed oral dosing in severely ill patients—one report noted serum ivermectin rising from 0.8 ng/mL after oral dosing to 5.8 ng/mL 16 hours after a first SC dose, and serial SC doses produced levels up to 7.9 ng/mL with evidence of metabolite accumulation and prolonged antiparasitic effect [3].
3. Controlled safety data — largely absent for parenteral routes in humans
Randomized or well‑controlled safety studies exist for oral ivermectin dosing (including dose‑escalation trials of high oral doses showing tolerability up to many times standard doses without clear CNS toxicity), but equivalent clinical trials testing SC or IM injectable formulations in humans are not available in the peer‑reviewed literature; therefore robust, generalizable safety data for injected ivermectin in people are lacking [4].
4. What the veterinary and pharmacology literature shows about IM/SC formulations and risks
Veterinary injectable ivermectin formulations are well characterized for cattle and swine, with documented dose regimens, oil‑based vehicles, and kinetic differences between SC and IM routes in animals—animal studies show prolonged plasma residence and altered absorption depending on formulation, which implies that small changes in vehicle or route can materially change human exposure if translated, a risk acknowledged in pharmacokinetic reviews [5] [6]. Veterinary labels and product monographs universally warn “not for use in humans” and list excipients (e.g., glycerol formal, propylene glycol) and residue warnings that further complicate direct human use [7] [8] [9].
5. Reported adverse events and regulatory stance
Accidental or significant exposure to veterinary ivermectin in humans has been associated with rash, edema, headache, dizziness, nausea, vomiting and diarrhea in case reports and summaries, and regulators (CDC guidance cited in case literature) acknowledge veterinary SC ivermectin as a possible last‑resort option but require IND oversight—this underscores that adverse effects have been observed with non‑standard exposures and that official pathways exist precisely because safety data are limited [10] [2] [1].
6. Gaps, hidden agendas and the potential for misuse
There is an implicit commercial and access tension: veterinary injectable products are widely available and engineered for livestock dosing, which has fueled off‑label attempts to use them in humans during crises, yet manufacturers and regulators explicitly prohibit human use and the literature repeatedly cautions that veterinary excipients and concentration differences matter for safety [7] [9]. Separately, broader debates around ivermectin for COVID‑19 led to increased public interest in non‑standard formulations, but existing authoritative reviews and drug databases emphasize the absence of quality evidence for injected human use and recommend approved routes and indications instead [10].
Conclusion — what can confidently be said
Conclusive human safety data for SC or IM injectable ivermectin simply do not exist beyond case reports, small pharmacokinetic observations, and extrapolation from animal studies; regulatory guidance treats veterinary injectable products as last‑resort, IND‑governed options when oral therapy is impossible, and the medical literature repeatedly calls for caution and controlled study rather than ad‑hoc use [1] [2] [5] [3] [4].