Lapachol [2-hydroxy-3(3-methyl-2-butenyl)-1,4-naphthoquinone] suspended in mineral oil and Freund's incomplete adjuvant administered by gavage to mice significantly reduced Schistosoma mansoni cercarial penetration and worm burdens between 8% and 100%, depending on dosage. High toxicity resulted from this treatment. Lapachol (0.9%) in the diet of mice reduced infection by 80% after 24 hours of feeding and by 96.9% after 3 days of feeding. Protection declined from 70% to 35% from 0 to 3 days after a single 24-hour feeding period. The sodium salt of lapachol at 0.5% in the drinking water reduced infection between 26.7% and 72.6%. Mice were protected from tail immersion and whole-body-wading challenge infections. Ultraviolet spectrophotometry demonstrated that the lapachol is secreted, presumably by the sebaceous glands, onto the skin where it acts as a topical barrier to penetration. Toxicity with dietary treatment (2,600 mg lapachol/kg mouse body wt./day) was limited to body-weight loss, which was completely recovered 7 days after treatment. No blood or histopathological changes were seen in mice treated for 4 days.
Present address: New York State Veterinary College, Cornell University, Ithaca, New York 14850.