Ivermectin (Mectizan, MSD) is now widely used to treat human onchocerciasis and lymphatic filariasis a successful broad-spectrum veterinary exo-and endoparasiticide . When used in humans, ivermectin has the added advantage of expelling large worm loads, including head lice in children . Thus the quality of life of rural dwellers in endemic communities is improved by ivermectin. However, lactating women within the first week of breastfeeding are excluded from community-wide distribution because of possible deleterious effects of ivermectin on their suckling newborns. Early research into ivermectin's antiparasitic activity against gutdwelling nematodes in domestic animals led to the proposal that ivermectin mimics the action of gamma-aminobutyric acid (GABA), the nematode-inhibitory neurotransmitter .
In order to ascertain the rationale for excluding lactating mothers from the benefit of ivermectin therapy, we studied the plasma and breast milk concentrations of the drug in four healthy mothers who had lost their babies at birth and had granted informed consent. Blood and breast milk samples were obtained after an overnight fast followed by oral administration of 150 gg. kg -~ ivermectin. Ivermectin was analysed by high-pressure liquid chromatography (HPLC) following derivatization and fluorescent detection as previously described ). Ivermectin was readily detected in the plasma and breast milk of all mothers within i h of drug administration and throughout the 24 h of observation. The mean plasma and milk concentration-time profiles of all four subjects are shown in Fig. . Ivermectin plasma levels ranged from 6.8 to 48.0 ng. ml-1 with a mean (SEM) of 22.6 (0.22) ng. mland in breast milk from 4.2 to 20.6 ng. ml -~ with a mean of 9.85 (0.38) ng. ml-~. Highest plasma concentrations (Cmax) ranged from 27.5 to 48.0 ng.ml -~ with a mean of 37.9