How long does ivermectin stay detectable in blood, stool, and hair?
Executive summary
Ivermectin is rapidly absorbed and cleared from blood with an elimination half‑life in humans of roughly 12–14 hours, and modern mass‑spectrometry methods can detect low nanogram‑per‑mL concentrations in plasma/whole blood down to ~0.5–1 ng/mL [1] [2]. Detectability in stool is more complex: veterinary data show parent drug residues can appear for weeks (up to ~40 days in horses), whereas human stool testing recommendations that extend for months reflect monitoring for parasite persistence or recrudescence, not direct measurement of lingering ivermectin [3] [4] [5]. Available sources do not document reliable human hair‑residue data for ivermectin; related animal/topical acaricide studies show residues on hair/skin for about a month but cannot be directly extrapolated to oral ivermectin in people [6].
1. Blood: quickly eliminated but measurable with sensitive assays
Pharmacokinetic studies report an elimination half‑life for ivermectin in human plasma around 12.6–13.4 hours after single oral doses, meaning blood concentrations fall by roughly half every 12–14 hours, and conventional sampling in early studies measured plasma up to 56 hours post‑dose [1]. Analytical LC‑MS/MS and sensitive HPLC/fluorometric assays can detect ivermectin at low ng/mL levels—the method validated for small human plasma or whole blood volumes reported a lower limit of quantification of ~0.97 ng/mL and a limit of detection of ~0.485 ng/mL [2]. Because ivermectin is lipophilic and distributes into tissues and skin, plasma concentrations are relatively low compared with total body burden, so “detectable” windows depend on assay sensitivity: highly sensitive methods can find traces beyond a couple of days, but standard clinical assays aligned with the drug’s half‑life imply that most blood levels fall below routine detection within several days [2] [7] [1].
2. Stool: drug residues vs parasite detection — two different clocks
Data from veterinary pharmacokinetics show that parent ivermectin can be measurable in feces for an extended period in some species, with one horse study reporting detectable faecal ivermectin concentrations for about 40 days after oral dosing [3]. In humans, however, the repeated stool testing recommended for months after treatment (for example, three stool exams over three months for strongyloidiasis) reflects monitoring for viable parasites or larvae and documented occasional recrudescence of larvae up to ~106 days post‑therapy, not persistence of the drug itself [8] [4] [5]. High‑sensitivity molecular assays (PCR) can detect parasite DNA long after treatment—sometimes for years in follow‑up studies—which can be misread as treatment failure if one conflates DNA detection with live parasites or drug presence [9]. The provided human sources do not supply direct, quantitative timelines for ivermectin parent‑drug detectability in human feces; veterinary data suggest weeks, but translating that to humans requires caution [3] [4].
3. Hair and skin: scant human data, animal/topical studies hint at month‑long residues
There is no direct human study in the provided material measuring oral ivermectin residues in hair. A topical veterinary/selamectin example shows detectable residues on hair/skin for about a month after application in dogs, demonstrating that lipophilic antiparasitic agents can persist on epidermal surfaces well beyond plasma clearance in animals [6]. Ivermectin’s documented distribution into skin and tissues in humans implies potential for some sequestration, but without human hair‑or‑skin residue studies in the supplied sources, any numeric claim about detectability in human hair would be speculative [2] [7]. The reporting therefore supports a cautious, evidence‑based conclusion: animal/topical analogues show ~1 month detectability on hair/skin, but no verified human hair detection timelines are present in the sources [6] [2].
4. What this means in practice and limits of the record
Practically, a single oral dose produces blood concentrations that decline rapidly (half‑life ~12–14 h) and are unlikely to be above routine detection beyond a few days to a week unless using highly sensitive MS methods that reach sub‑ng/mL limits [1] [2]. Fecal drug residue data come mainly from animals (up to ~40 days) while human stool testing timelines in clinical guidance reflect parasite recovery/relapse risk rather than pharmacokinetic drug persistence [3] [4] [5]. There is an explicit limitation in the reviewed literature: no direct human studies in these sources quantify oral ivermectin residues in hair, and several human sources focus on parasite monitoring rather than measuring drug concentrations in stool or hair [6] [9] [8]. Where alternative viewpoints exist—for example differing species, formulations (topical vs oral), or assay sensitivities—the sources indicate these variables materially change detectability windows and must be considered when interpreting any test result [6] [2].