Use of clays as drug delivery systems: possibilities and limitations

The need for safe, therapeutically effective and patient-compliant drug delivery systems continuously leads researchers to design novel tools and strategies. Clay minerals are widely used materials in drug products both as excipients and active agents. When administered simultaneously, drug–clay interactions have been observed and studied, but until recently were not considered as a possible mechanism to modify drug release. In recent years, and based on their high retention capacities as well as swelling and colloidal properties, clays have been proposed as very useful materials for modulating drug delivery. This paper first reviews the studies on drug–clay interactions, and then those focused on the applications of natural clays and their semi-synthetic or synthetic derivatives to carry out specific functions in new drug delivery systems. In particular, clays are used to delay and/or target drug release or even improve drug dissolution. Finally, new strategies are reported for increasing drug stability and simultaneously modifying drug delivery patterns through the use of clay minerals.