The chemotherapy of onchocerciasis X. An assessment of four single dose treatment regimes of MK-933 (ivermectin) in human onchocerciasis.

Nineteen patients from an area of vector control in the savanna region of Northern Ghana, all with moderate to heavy infections with Onchocerca volvulus and some with ocular involvement, were treated with 50, 100, 150 or 200 micrograms kg-1 of ivermectin. Detailed monitoring of clinical and ocular reactions and of alterations in skin microfilarial counts and laboratory indices were carried out during the first 28 days. Microfilarial counts in skin snips and detailed ocular examinations were then repeated at intervals over a period of nine months. Ivermectin slowly eliminated microfilariae from the skin and eye without serious adverse clinical or ocular reactions in all treated groups. There was little difference in efficacy between doses of 100, 150 and 200 micrograms kg-1, and these were more effective than the 50 micrograms kg-1 dose. Very low levels of skin microfilariae were maintained for nine months. Microfilariae were not eliminated from the eye for at least three months. The drug was neither macrofilaricidal nor embryotoxic. However, it produced a dose-dependent stimulation of embryogenesis manifest at one month and succeeded by a suppression of embryogenesis at three months after therapy. In areas where transmission of onchocerciasis has been interrupted, ivermectin may need not be given more often than once a year. The efficacy of the drug on single dosage and the mild adverse reactions produced, if confirmed in subsequent controlled studies, would greatly simplify the treatment of onchocerciasis and would reintroduce new concepts of the role of chemotherapy in the control of onchocerciasis.