The in vitro diffusion of the organophosphate famphur from polydimethylsiloxane (PDS) capsules into plasma and their effects on Litomosoides carinii and Dipetalonema witei in jirds was studied. The in vitro rate of diffusion per 24 hours was constant and was directly proportional to the capsule lumen surface area and inversely proportional to the capsule wall thickness. One capsule implanted subcutaneously into each jird almost completely eliminated the microfilaremia of L. carinii while in situ (5 weeks) but had no effect on the levels of microfilaremia of D. witei. The adults of both species were unaffected. The capsules were well tolerated by the jirds and little tissue response to them was noted. The possibilities of using PDS-incapsulated drugs for prophylactic chemotherapy of canine and human filariasis is discussed.
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