Evaluation of cutaneous absorption and safety of idoxuridine after topical administration

The absorption of a preparation of the antiviral drug 5-iodo-2'-deoxyuridine (idoxuridine or IDU] has been assessed in rats. A 40% w/v solution of 3H-IDU in dimethyl sulfoxide (DMSO) was topically applied to rats; cutaneous absorption was determined by morphometric evaluation of autoradiographic preparations of the skin. Passage of the drug to the bloodstream was followed using radioisotopic techniques. In addition, the potential irritative action of the same preparation of IDU was investigated in a more suitable animal model. A predictive guinea pig sensitization study was performed according to the Magnusson and Kligman method. 3H-IDU was detected in the epidermis of the rat 60 min after local application. However, it was not possible to determine noticeable levels of the radiolabelled drug in the circulating blood. Experiments on guinea pigs showed slight transient erythematous responses in three animals of the test group following first challenge, and in one animal of the test group and one of the control group, following the second challenge. The overall results of the sensitization test were negative. These results give experimental support for the safety of the IDU preparation studied.