Atomistic simulation study of surfactant and polymer interactions on the surface of a fenofibrate crystal

It is currently of great interest to the pharmaceutical industry to control the size and agglomeration of nano- and micro-particles for the enhancement of drug delivery. Typically, surfactants and polymers are used as additives to interact with and stabilize the growing crystal surface, thus controlling size and agglomeration; however, selection is traditionally done empirically or using heuristics. The objective of this study was to use molecular dynamic simulations to investigate and predict additive interactions, and thus, evaluate the stabilization potential of individual and multiple additives on the surface of the model drug fenofibrate. Non-ionic surfactant Tween 80, anionic surfactant sodium dodecyl sulfate (SDS), and polymers hydroxypropyl methylcellulose (HPMC) and Pullulan were evaluated individually on three distinct crystal surfaces [(001), (010), (100)], as well as in surfactant-polymer combinations. HPMC was determined to have the strongest interaction with the surfaces of the fenofibrate crystal, and therefore, was predicted to be the most effective individual additive. A mixture of HPMC with SDS was determined to be the most effective mixture of additives, and more effective than HPMC alone, indicating a synergistic effect. The predictions of mixed additives indicated a relative order of effectiveness as follows: HPMC-SDS>HPMC-Tween 80>Pullulan-Tween 80>Pullulan-SDS. The simulations were subsequently validated by an anti-solvent crystallization of fenofibrate where it was found that HPMC individually, and a mixture of HPMC-SDS, produced the smallest and most stable crystals, as measured by laser diffraction; this, in combination with measurements of the crystal growth rate in the presence and absence of additives confirmed the results of the simulations.