High oral doses of mebendazole are used experimentally for the treatment of human alveolar and cystic echinococcosis. In order to assess bioavailability of this drug 1.5 g doses were given to 3 volunteers. Measurable plasma concentrations of 17 to 134 nmol/l were found only if mebendazole was given together with a fatty meal. In a patient with cholestasis plasma concentrations were higher than in the 3 normal subjects. In patients on long term treatment the increase in plasma concentration after administration of a 1 g dose varied between 0 and 500 nmol/l. It is concluded that systemic availability of mebendazole is enhanced by concomitant food intake. In view of the large intra- and interindividual variation in plasma concentration, monitoring plasma levels during long term therapy appears advisable.

SummaryA procedure for determining the anthelmintic drug mebendazole in plasma of patients is described. Mebendazole together with the internal standard ciclobendazole is extracted with chloroform at pH 11. The extract is analyzed isocratically on a LiChrosorb SI 60 column with a mobile phase consisting of acetonitrile / water-saturated chloroform / ammonia (75/92.5/0.1) at 307 nm. Reproducibility with a coefficient of variation of 3 to 10% is attainable for the concentration range of 20 to 200 ng mebendazole / ml plasma. Mebendazole plasma concentrations in patients with echinococcosis on chronic therapy with mebendazole ranged from 6 to 11 7 ng/ml.

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