Drug Resinates an Attractive Approach of Solubility Enhancement of Atorvastatin Calcium

A substantial number of new chemical entities and marketed drugs show poor solubility characteristics and amorphisation is one of the favorable approaches to enhance solubility characteristics of such poorly soluble drugs. Formulation efforts in the present study were devoted to investigate amorphisation of a model poorly soluble drug, atorvastatin calcium by molecular complexation with anion exchange resin, Duolite^®AP 143/1093 and hence enhancement in its solubility characteristics. Drug resinates in 1:1, 1:2, and 1:4 weight ratios were prepared by simple batch operation and subsequently studied for drug content, residual solvent content, molecular interactions, solid state characterisation and solubility characteristics. During initial characterisation, all the proportions of drug resinates, except 1:1 proportion showed partial amorphisation of the drug, whereas 1:1 proportion showed complete amorphisation of the drug. This proportion reported distinctly enhanced solubility characteristics over pure drug and other proportions. Such amorphisation and solubility enhancement could be attributed to the binding of individual drug molecules to the functional sites of the resin molecules, either partially or completely, resulting in reduction of crystal lattice energy, a main barrier to dissolution. Hydrophilic nature of ion exchange resin matrices also assisted in enhancing dissolution of the drug from the resinates. During accelerated stability study, there was an insignificant decrease in solubility characteristics of the drug and its amorphous form was also found to be stable in 1:1 proportion. Atorvastatin resinates formed in 1:1 weight ratio were in stoichiometric proportion and such drug resinates in stoichiometric proportion showed to have tremendous potential in conversion of crystalline form of drug substances to its amorphous form and subsequent stabilisation. It hence proved to be a very effective, yet simple approach for improving solubility characteristics of poorly soluble actives.