Safety and efficacy of 3- and 5-day regimens of levamisole in loiasis: a randomized, placebo-controlled, double-blind clinical trial.

Individuals with high Loa loa microfilarial densities (MFD) risk serious adverse events (SAEs) following ivermectin treatment. A single dose of levamisole (LEV) induces a temporary, progressive MFD decrease. This double-blind, randomized, placebo-controlled trial evaluated the safety and efficacy of 3-day and 5-day LEV regimens for the treatment of loiasis in the Republic of the Congo. Participants were randomly assigned to receive placebo (PLA), LEV-3, or LEV-5. Safety was assessed by the occurrence of SAEs and the frequency and severity of AEs. Efficacy was measured by changes in Loa loa MFD. No SAEs were reported, and AE severity was comparable across treatment arms. On day 5, MFD reductions were greater in the LEV-3 and LEV-5 groups compared to PLA ( -1.6%, 29.3%, and 51.4%, respectively; P < 0.001). By day 7, a higher proportion of participants achieved ≥40% MFD reduction in the LEV-5 group (44.4%) compared to LEV-3 (34.6%) and PLA (8.3%) (P = 0.051). Post hoc contrasts confirmed significantly greater MFD reduction with LEV-5 versus LEV-3. These findings suggest that a 5-day LEV regimen is safe and moderately effective for reducing L. loa MFD and may represent a promising alternative for individualised management in loiasis-endemic areas, particularly where onchocerciasis is hypoendemic and coendemic with loiasis. Trial registration: NCT06252961.