R. E. Howells

The chemotherapy of onchocerciasis VIII Levamisole and its combination with the benzimidazoles.

In two separate studies the antifilarial activity of levamisole, mebendazole and their combination, and of flubendazole combined with levamisole, were investigated in a total of 96 patients. Ten patients received levamisole 2·;5 mg kg−1 on two occasions during the first week and then weekly for three weeks. Twelve patients received mebendazole 30 mg kg−1 daily in divided doses for three weeks. Thirteen patients received a combination of levamisole and mebendazole. In 12 patients mebendazole was given after two ‘priming’ doses of levamisole. A control group of 11 patients received vitamin preparations. In the second study 20 patients received flubendazole 30 mg kg−1 daily in divided doses for three weeks combined with levamisole 2·5 mg kg−1 given on two occasions in the first week and then weekly. A control group of 18 patients received vitamin preparations. The microfilaricidal effect of the drug regimes was determined by weekly skin snips during and one week after completion of therapy.Levamisole was ine...

The exsheathment of Brugia pahangi microfilariae under controlled conditions in vitro

Two reproducible techniques for the exsheathment in vitro of microfilariae of Brugia pahangi, and other sheathed microfilariae, are described. Microfilariae were isolated from infected cat blood by filtration and suspended in Hanks Balanced Salt Solution. The first technique involved the incubation of isolated microfilariae for one hour in 20 mM CaCl2 in a phosphate-free Balanced Salt Solution, during which time approximately 90% of the microfilariae lost their sheaths. The second method of exsheathing microfilariae of B. pahangi involved exposure of microfilariae to solutions of endopeptidase (5.8 units/ml) or papaya extract protease (3.0 units/ml) in Ca2+-free HBSS. Exsheathment rates of 95--100% occurred within 30 minutes in both enzyme solutions. Both the Ca2+ ion and the endopeptidase technique have proven equally effective in stimulating exsheathment of microfilariae of Brugia malayi, Wuchereria bancrofti and Litomosoides carinii. Such artificially exsheathed microfilariae are used for in vitro cultivation studies. The viability of Ca2+- and endopeptidase-exsheathed microfilariae of B. pahangi has been confirmed by inoculation of exsheathed larvae into susceptible female mosquitoes.

Brugia pahangi in the BALB/C mouse: a model for testing filaricidal compounds.

The BALB/C mouse infected with Brugia pahangi has been evaluated as a model for the selection of filaricidal compounds with activity against immature worms. Mice were infected by the intraperitoneal inoculation of 50 infective larvae and candidate compounds were administered by the intraperitoneal (i.p.), subcutaneous or oral route once daily from day 4 to day 8 post infection. Animals were examined on days 29 to 32 post infection. Variation in the larval recoveries from undrugged mice within and between experimental groups limited the value of drug assessments based upon percentage worm recoveries. The infection rate of undrugged mice was 85% over-all, range 60 to 100%. Using the infection rate of drugged v. undrugged animals as the criterion of activity the test has been evaluated with a series of standard nematicidal compounds. Levamisole and the benzimidazole carbamates, mebendazole, flubendazole and fenbendazole given i.p. at 10 mg/kg daily were active in this screen whilst DEC, DEC-N-oxide, ivermectin, amoscanate, metrifonate and suramin were inactive at the dosages tested. No retardation of growth or morphological abnormalities were observed in worms from the drugged mice.

Combination of the antibiotics erythromycin and tetracycline with three standard antimalarials against Plasmodium falciparum in vitro

Combinations of antibiotics and standard antimalarials have been assayed against P. falciparum in vitro, using incorporation of 14C isoleucine as an indicator of drug action. Chloroquine and erythromycin have been shown to act synergistically against a chloroquine-resistant strain and additively towards a chloroquine-sensitive strain, confirming their action against sensitive and resistant P. berghei in vivo, described elsewhere. Combinations of erythromycin with mefloquine or quinine acted anergically in 24 hour assays in which unphysiologically high concentrations of quinolinemethanol were necessary for demonstrable drug effect. In 48 hour assays, an additive effect was obtained with these combinations. Tetracycline is additive in combination with each of the standard antimalarials used in this study. The relevance of results obtained in vitro to parasite drug sensitivities in vivo is discussed.

A comparison of the pyrimethamine and cycloguanil sensitivities of the pre-erythrocytic and erythrocytic stages of drug-sensitive and -resistant strains of Plasmodium yoelii

The cycloguanil and pyrimethamine sensitivities of the pre-erythrocytic and erythrocytic stages of a drug-sensitive and drug-resistant strain of Plasmodium yoelii have been compared. With both compounds, and in both parasite strains, the pre-erythrocytic stages were more sensitive to inhibition than were the erythrocytic stages. In the resistant strain the increase in the level of drug tolerance in the erythrocytic stages was paralleled by a corresponding loss of sensitivity in the pre-erythrocytic stages.

A simple method for the identification of compounds which inhibit tubulin polymerization in filarial worms

The incubation in vitro of excised ovaries of Dirofilaria immits in medium containing mebendazole between 10(-5) and 10(-8) M for four or six hours results in the accumulation of up to 20% of oogonial cells in arrested mitotic metaphase. In aceto-orcein-stained squashes of the tissue, cells possess condensed chromosomes but no detectable spindle microtubules. Similar results were obtained with colchicine, but the lowest effective concentration of this drug was 10(-7) M. This procedure affords a simple and rapid method for detecting compounds capable of inhibiting tubulin polymerization in filarial worms.