Drug: Ivermectine

A systematic review and meta-analysis of 282 records from 238 distinct foci across 19 sub-Saharan African countries found that sustained mass drug administration of ivermectin drives onchocerciasis toward elimination of transmission. Ten or more years of treatment at 80% or higher coverage, 15 to 19 years of treatment, and twice-yearly dosing were each strongly associated with reaching or approaching elimination. Elimination of transmission was reported in 9% of records and being close to it in a further 30%. Ivermectin kills the microfilariae, not the long-lived adult worms, so repeated rounds over many years are needed and 61% of records still showed ongoing transmission. Elimination depends on sustained high coverage, not the drug alone.

In a randomized trial in Papua New Guinea, a single dose of ivermectin plus diethylcarbamazine plus albendazole cleared Wuchereria bancrofti microfilariae from the blood in 96% of participants at both 12 and 24 months, against 32% at 12 months for a single dose of the standard two-drug regimen. At 24 months clearance was 56% after a single dose of the two-drug regimen and 75% after two annual doses of it, so the single triple-drug dose was superior to both, matching in one treatment what the two-drug regimen needs repeated annual rounds to achieve. Moderate short-term reactions were more common with the three-drug dose than the two-drug regimen, 27% against 5%, with no serious adverse events. This was 182 adults in one setting.

In a multicenter randomized trial across Italy, Spain and the UK, a single 200 microgram per kilogram dose of ivermectin cleared Strongyloides stercoralis infection at 12 months in 86% of participants, statistically indistinguishable from four doses at 85%. The trial was stopped early for futility because extra doses added no benefit and were tolerated less well, establishing the single dose as the standard. This was measured in a non-endemic population with mostly imported, non-disseminated infection. Severe disseminated strongyloidiasis and hyperinfection in people who are immunocompromised are managed differently. The trial was open-label.

In a Fijian trial that assigned island communities to different strategies, one round of mass ivermectin cut scabies prevalence from 32.1% to 1.9% at 12 months, a 94% relative reduction, the largest of any group, and cut impetigo, the skin infection scabies drives, by 67%. This was three island communities, so few independent units sit behind the summary figure. Mild adverse events were more frequent with ivermectin than permethrin, 15.6% against 6.8%, and it is a single trial in one region.

In two randomized, double-blind trials, a single 10-minute application of 0.5% ivermectin lotion, with no nit combing, left 94.9% of patients louse-free the day after treatment and 73.8% still louse-free at day 15, against 17.6% for the vehicle control. Adverse events were similar in both groups. The trials were funded by the product maker, they tested a specific topical formulation, not tablets, and the day-15 figure shows clearance is high but not complete.

In two identically designed, randomized, double-blind, vehicle-controlled pivotal trials, once-daily ivermectin 1% cream for 12 weeks achieved treatment success, rated clear or almost clear, in 38.4% and 40.1% of people with moderate-to-severe papulopustular rosacea, against 11.6% and 18.8% on the vehicle cream. Inflammatory lesion counts fell 76.0% and 75.0% from baseline, against 50.0% for the vehicle. These were manufacturer-sponsored trials of a topical cream for papulopustular rosacea, a use separate from the oral antiparasitic role. Rosacea is linked to Demodex skin mites, which the cream is thought to target, and treatment success here means clear or almost clear, not a cure.

The three largest randomized trials in outpatients agree. TOGETHER found a relative risk of 0.90 (credible interval 0.70 to 1.16) for hospitalization or extended emergency observation. ACTIV-6 found a recovery hazard ratio of 1.07 (0.96 to 1.17), a median 12 versus 13 days, with 10 versus 9 hospitalizations or deaths. PRINCIPLE, the largest at 8811 participants, found recovery a median 2.06 days faster but well below its own threshold for a meaningful effect, with no difference in hospitalizations, deaths, or recovery at six months. These trials studied mild-to-moderate outpatient COVID, largely in vaccinated populations. PRINCIPLE did detect a small recovery-time difference, but one its investigators had defined in advance as too small to be clinically meaningful, and it did not carry through to hospitalization or long-term recovery.

A Cochrane review that excluded 7 of 14 earlier trials for failing prospective registration or integrity checks pooled the remaining evidence. For outpatients it found moderate-certainty evidence of little or no effect on all-cause mortality (risk ratio 0.77, 95% confidence interval 0.47 to 1.25, 6 trials, 2860 participants) and high-certainty evidence of no effect on quality of life. The picture held once the trials with the weakest methods were set aside. Evidence for inpatients with severe disease remained very low certainty, so no strong claim can be made there. The strength of this review is what it excluded: seven trials that were not prospectively registered or were not randomized, including work later withdrawn for data problems.

Ivermectin binds glutamate-gated chloride channels found in the nerve and muscle cells of invertebrates. Binding opens the channels, chloride floods in, the cells are hyperpolarized, and the parasite is paralyzed and dies. Mammals do not use these channels at the nerve-muscle junction, and an intact blood-brain barrier keeps the drug out of the mammalian central nervous system, which is the basis of its wide safety margin at approved doses. The selectivity depends on the blood-brain barrier holding the drug out of the brain. The same channel family exists in the mammalian central nervous system, so very high doses, or a compromised barrier, can produce neurological effects, which is the mechanism behind overdose toxicity.

An early laboratory study reported that adding ivermectin to infected monkey kidney cells produced roughly a 5000-fold reduction in SARS-CoV-2 RNA at 48 hours. The concentration required was many times higher than the blood and lung levels reachable in a person at approved or tolerable oral doses, which is the gap the later clinical trials had to test. A cell-culture result at a concentration that cannot be achieved safely in people does not establish a clinical effect. This finding launched the clinical question; it did not answer it. The large trials that followed found no meaningful benefit.