AbstractBackgroundTopical corticosteroids (TCS) and emollients are developed independently by the pharmaceutical industry but are often used together in practice. There is potential for the TCS and emollient formulations to interact on the skin surface affecting TCS absorption into the skin. Clinical guidelines acknowledge this issue but lack an evidence base and differ in their recommendations. There is a current clinical need to establish whether the application protocol employed for TCS and emollient products can impact delivery of TCS to the skin.ObjectivesTo investigate whether the sequence of application of a TCS and emollient and the time between their application can affect TCS skin absorption.MethodsThe delivery of mometasone furoate (MF) to ex vivo human skin was evaluated following the application of Elocon cream either 5 or 30 min, before and after three different emollients. Mechanistic explanation of the changes in drug absorption was provided by modelling the skin permeation data and Raman microscopy of mixed Elocon cream and emollient formulations.ResultsA circa fivefold difference in MF absorption was observed depending on the emollient and application protocol. Applying Elocon cream at short intervals in relation to Hydromol intensive significantly increased MF absorption regardless of the application protocol. In contrast, applying Elocon cream after Diprobase cream or ointment significantly reduced MF absorption relative to Elocon cream alone or when Elocon cream was applied before these emollients. The changes in drug absorption observed were attributed to the presence of emollients altering Elocon cream formulation performance through different mechanisms, including introduction of penetration enhancing excipients and inducing drug crystallization in the mixed TCS emollient layer on the skin surface.ConclusionsEmollients can affect MF absorption in different ways depending on the emollient and sequence of administration. Using a 30 min gap between product applications may not be sufficient to mitigate emollient effects on TCS absorption.