The efficacy of 22,23-dihydroavermectin B1 (ivermectin) acting singly or in combination with a benzodiazepine on microfilariae of Onchocerca species and Brugia pahangi (an in vitro study)

Abstract

An in vitro study of the antinematodal action of two groups of compounds which act on the receptor complex of the inhibitory neurotransmitter, Gamma-aminobutyric acid (GAGA) in mammalian systems is described. The compounds, Ivermectin and two benzodiazepines, Diazepam and a water soluble Midazolam were tested singly or in combination against two microfilarial parasites Onchocerca lienalis (closely related to Onchocerca volvulus) and Brugia pahangi. The combination of ivermectin and diazepam at a concentration of 0.1 µg/ml and 33 µg/ml respectively achieved the same effect on microfilarial motility as when ivermectin was given at 1 µg/ml alone or diazepam at 66 µg/ml alone. Similarly, when the combination of ivermectin at 0.1 µg/ml and midazolam at 10 µg/ml was used it achieved the same effect as ivermectin at 1 µg/ml alone or midazolam at 33 µg/ml alone. This showed that both benzodiazepines had a synergistic effect on the activity of ivermectin. The microfilariae of B. pahangi were insensitive to both groups of compounds at all concentrations used.