Which completed randomized ivermectin trials reported on pre‑exposure or post‑exposure prophylaxis and what were their dosing regimens?

1. The randomized trial most frequently cited as prophylaxis: Ivercar‑Tuc and its dosing

A 1:1 randomized trial labelled Ivercar‑Tuc (reported as a medRxiv preprint and discussed across reviews) tested an “intensive” prophylactic approach in healthcare workers in Tucumán, Argentina: the experimental arm received oral ivermectin 2 × 6 mg tablets (12 mg total) every seven days plus iota‑carrageenan nasal spray six times per day for four weeks, and the trial reported fewer infections in the treated group versus control ^{[1] [4]}.

2. Other randomized prophylaxis signals reported in reviews — sparse details and mixed formats

Systematic reviews and meta‑analyses that compiled randomized trials list several prophylaxis studies and cluster trials but rarely provide full dosing details for all randomized prophylaxis arms in their summaries; reviewers note some prophylaxis RCTs (including ones combining ivermectin with other agents) but emphasize small sample sizes and heterogeneous regimens, which limits pooled inference ^{[5] [3] [6]}.

3. Trials that were randomized but not principally prophylactic (and dosing referenced in treatment trials)

Several rigorously randomized trials focused on treatment rather than prophylaxis but have been cited when discussing possible prophylactic regimens: pilot and treatment RCTs tested single doses (for example a 400 µg/kg single dose in an early treatment pilot) and multi‑day higher‑dose schedules (for example targeted 600 µg/kg daily for six days in a large outpatient platform trial), illustrating the wide range of dosing strategies explored even outside prophylaxis studies ^{[7] [8] [9]}.

4. What authoritative reviewers conclude about prophylaxis evidence and recommended doses

Major evidence syntheses — Cochrane and the BMJ living prophylaxis review — conclude that reliable evidence is lacking to support ivermectin for prevention after exposure and that completed randomized trials are small and of uncertain quality; Cochrane explicitly found no solid evidence for post‑exposure prevention and categorized dosing schemes variably as low (≤0.2 mg/kg single dose) or high (>0.2 mg/kg or repeated dosing) when synthesizing trials ^{[2] [10]}. The BMJ and other commentators suggested, early in the pandemic, that pragmatic prophylaxis trial designs could test two single doses a week apart, a regimen used in some compassionate or pilot contexts, but this was a methodological suggestion rather than evidence of efficacy ^[11].

5. Limits of the published randomized prophylaxis record and how to interpret dosing claims

The public‑facing literature mixes peer‑reviewed RCTs, preprints, observational cohorts, and combination intervention trials (ivermectin plus iota‑carrageenan), and many systematic reviews pool disparate dosing schemes (single low dose, weekly low fixed tablet doses, multi‑day high microgram‑per‑kg regimens) without a uniform protocol; as a result, precise, consistently reported prophylactic dosing across completed randomized trials is limited in the available sources and reviewers caution against extrapolating single trial regimens into practice until larger, high‑quality RCTs confirm benefit and safety ^{[1] [5] [2]}.

6. Bottom line for prophylaxis dosing: what can be stated with confidence

Only a small number of randomized studies explicitly tested ivermectin for pre‑exposure prophylaxis, the best‑documented randomized pre‑exposure regimen in the available record used weekly 12 mg oral ivermectin plus daily nasal iota‑carrageenan sprays for four weeks (Ivercar‑Tuc) ^[1], while other randomized trials addressed treatment with diverse dosing (single 400 µg/kg, or multi‑day regimens up to 600 µg/kg/day) and reviewers conclude the overall randomized evidence does not support routine prophylactic use pending robust, consistent RCT data ^{[7] [8] [2]}.