Development of microemulsion of mitotane for improvement of oral bioavailability

Mitotane (o,p'-DDD) is considered to be the drug of choice in the treatment of nonresectable and metastasized adrenocortical carcinoma. However, mitotane has poor solubility in the gastrointestinal tract and very low bioavailability. Consequently, to achieve therapeutic plasma level, high cumulative doses (4-6 g/day) of mitotane were usually used during 3-5 months. To shorten this equilibration time and reduce gastrointestinal side effects, a self-microemulsifying drug delivery system (SMEDDS) of mitotane has been developed.

First time, the solubility of mitotane was determined in various oils and surfactants; then, the influence of oils, surfactants, and cosurfactants on the formation of SMEDDS was investigated by constructing ternary phase diagrams. SMEDDS was characterized by morphological observations and droplet size measurements. Intestinal drug permeation of SMEDDS of mitotane (3 mM) was assessed in an Ussing-type apparatus and the bioavailability was determined in a rabbit model.

The optimum formulation consisted of a mixture of Capryol, Tween, and Cremophor EL (33:33:33). The formulation was found to pass through the intestinal barrier much faster than a solution of mitotane (14.85 +/- 0.8 versus 3.03 +/- 0.2 micromol/cm(2)). Moreover, after oral administration in rabbits, the relative bioavailability was 3.4, compared with that of the conventional form (Lysodren).

This SMEDDS can now be considered as a very good candidate to optimize the administration of mitotane.