Impact of antinucleants on transdermal delivery of testosterone from a spray

The goal was to explore whether the incorporation of antinucleant polymers into a testosterone spray formulation could stabilize a putative supersaturated state and improve the delivery of the drug across the skin. Several antinucleants were screened using differential scanning calorimetry (DSC) and two candidates showed particular promise: a cyclodextrin derivative (RAMEB) and a vinylpyrrolidone/vinyl acetate copolymer (Kollidon VA64). These agents also improved significantly the long-term stability of saturated solutions of the drug. Further, using the method of mixed cosolvents, it was possible to create, in the presence of 5% w/v antinucleant polymer, supersaturated ethanol/propylene glycol/water (4:1:1 v/v) solutions of the drug with degrees of saturation between 1.4 and 2.6; however, these metastable systems existed only transiently under carefully controlled conditions and had reverted back to equilibrium solubilities of the drug within 6 h. When the same solutions were administered to hairless rat skin in vitro from mechanical sprays, no improvement in testosterone delivery, relative to a nonstabilized control, was observed. It appears, therefore, that the in situ crystallization process of the drug is more complex and incompletely understood (and cannot be predicted from DSC experiments). The complicated evaporation/volatilization process, which takes place when a spray is pulverized, requires better characterization before the use of supersaturation for testosterone delivery can be optimized.