Safety, Efficacy of Levamisole in Individuals With Loiasis Infection

loa loa infection
Loa Loa, Posterior End. It Is The Causative Agent Of Loiasis Filariasis. (Photo By BSIP/UIG Via Getty Images)
Researchers conducted a study to assess the safety and efficacy of levamisole in individuals with loiasis parasitic infection.

A single dose of levamisole was found to be safe and temporarily decreased microfilarial densities (MFD) of Loa loa among individuals with loiasis parasitic infection, according to results of a double-blind, randomized, placebo-controlled trial published in Clinical Infectious Diseases.

Individuals (N=389) with a loiasis parasitic infection were recruited in 2019 by the Congolese administrative department of Lékoumou in the Republic of Congo. Participants were stratified into 3 cohorts by baseline MFD and levamisole dose. Among the 3 cohorts, cohort 1 comprised participants (n=81) with low MFD (1-1999 mfs/mL) who were randomly assigned in a 1:1:1 fashion to receive either levamisole 1 mg/kg, levamisole 1.5 mg/kg, or placebo. Cohorts 2 (n=111) and 3 (n=63) comprised participants with MFD between 1 and 14,999 mfs/mL and MFD greater than or equal 14,999 mfs/mL, respectively. Participants in cohorts 2 and 3 were randomly assigned in a 1:1 fashion to receive either levamisole 2.5 mg/kg or placebo; Loa MFD was assessed through day 30.

The study population comprised more men than women and participants were aged between 18 and 65 years.

Among participants in cohort 1, there were no reports of severe adverse events and 15 reported mild or moderate adverse events of mild and moderate severity. Of note, the researchers found no significant changes in MFD between the 3 cohorts (P >.05).

Among participants in cohorts 2 and 3, there were no severe adverse events observed and 17 reported mild and transient adverse events, of which 13 were related to the trial. The researchers found that the frequency of adverse events was increased among participants who received levamisole compared with those who received placebo (P =.018). Of note, participants who had an adverse event were found to have significantly increased baseline MFD (mean, 19,645 vs 9877 mfs/mL; P =.020).

The researchers found that the median MFD of Loa loa were significantly decreased among participants who received levamisole 2.5 mg/kg vs those who received placebo at days 2 (P =.001), 7 (P =.001), and 30 (P =.036). In addition, the proportion of participants who had a 40% decrease in MFD at day 2 was significantly increased among those who received levamisole 2.5 mg/kg vs those who received placebo (P <.001); however, this trend was no longer statistically significant by day 7 (P =.269).

Overall, there was high variability of MFD reduction among participants included in the study.

This study may have been limited by its inclusion of participants with differing baseline MFD.

The researchers noted that these results “…suggest a possible effect of [levamisole] on Loa MFD at a dose that is well-tolerated.” In addition, “other trials using higher doses or repeated doses [of levamisole] for several days are needed to identify the most effective [treatment regimen],” the researchers concluded.


Campillo JT, Bikita P, Hemilembolog M, et al. Safety and efficacy of levamisole in loiasis: a randomized, placebo-controlled, double-blind clinical trial. Clin Infect Dis. 2021;ciab906. doi:10.1093/cid/ciab906