Dapsone (DAP) is a synthetic sulfone drug with bacteriostatic activity, mainly against Mycobacterium leprae. In this study we have investigated the interactions of DAP with cyclodextrins, 2-hydroxypropyl-b-cyclodextrin (HPbCD) and b-cyclodextrin (bCD), in the presence and absence of water-soluble polymers, in order to improve its solubility and bioavailability. Solid systems DAP/HPbCD and DAP/bCD, in the presence or absence of polyvinylpyrrolidone (PVP K30) or hydroxypropyl methylcellulose (HPMC), were prepared. The binary and ternary systems were evaluated and characterized by SEM, DSC, XRD and NMR analysis as well as phase solubility assays, in order to investigate the interactions between DAP and the excipients in aqueous solution. This study revealed that inclusion complexes of DAP and cyclodextrins (HPbCD and bCD) can be produced in order to improve DAP solubility and bioavailability in the presence or absence of polymers (PVP K30 and HPMC). The more stable inclusion complex was obtained with HPbCD, and consequently HPbCD was more efficient in improving DAP solubility than bCD, and the addition of polymers had no influence on DAP solubility or on the stability of the DAP/CDs complexes.

Transdermal applications of drugs present many advantages in terms of absorption, however this is not easily obtained through the transdermal route. The principle barrier is the stratum corneum and one of the strategies that have been found to promote cutaneous drug penetration is through the use of absorption enhancers. Many substances have been identified as absorption enhancers. Although the list of substances that promote absorption is growing, in most cases, there is a direct correlation between the effects of absorption enhancers and their skintoxicity. The use of these substances depends therefore on studies which focus on local and systemic toxicity, as well as action mechanisms.