[Acaricidal activity of "Medifox" against the human itch mites Sarcoptes scabiei]

The acaricidal activity of Medifox was evaluated in terms of the itch mites to lend support to the validity of its regimen to treat human scabies. Experiments using mainly females, eggs, and larvae withdrawn from the burrows on the skin of patients with scabies were performed. Permethrin contained in 0.4% aqueous Medifox emulsion was found to affect an itch mite by contact and intestinal routes, without a marked knock-down effect; however, the signs of intoxication are irreversible and lead to the death of Medifox-treated mites. In an in vitro experiment, 100% death of specimens occurred 24-48 hours after immersion of the active stages in the aqueous emulsion for 1 min, depending on the stage of their development. Visual inspection of the course of embryogenesis and the hatch of larvae from eggs under a light microscope established that 20-40-min exposure to Medifox emulsion did not prevent the final formation of a larva and its hatch if the egg was at the late stages of embryogenesis. Long-term (180-min) exposure yielded a 100% ovicidal effect. An in vivo experiment indicated that there were no viable mites in the scabies burrows after single-to-double treatment of patients. Repeated applications are required due to their incomplete ovicidal effect. As a matter of fact, the third treatment is additional to create the "safety factor" of therapy. It is concluded that there is an agreement of the results of in vitro and in vivo experiments, by studying Medifox as an example. The findings suggest that the chosen Medifox treatment regimen including three consecutive treatments results in complete eradication of all the stages of the causative agent on the patient.