Evaluation of solid lipid microparticles produced by spray congealing for topical application of econazole nitrate

The aims of this study were to evaluate the feasibility of solid lipid microparticles (SLM) suitable for topical administration using the spray congealing technique and to study the skin permeation of a drug from SLM in comparison with solid lipid nanoparticles (SLN). Econazole nitrate was employed as model drug and Precirol ATO 5 as lipidic carrier. SLM and SLN were both prepared at 5:1, 10:1 and 12.5:1 lipid to drug weight ratios. SLM had particle size from 18 to 45 micron, while SLN showed a mean diameter between 130 and 270 nm; the encapsulation efficiency ranged from 80 to 100%. SLM and SLN were then incorporated into HPMC K 100M hydrogels and ex-vivo drug permeation tests were carried out. The results show that the permeation rate of ECN depends both on the particle size and on the amount of lipid used: at high drug loading, SLM gels can improve the permeation rate of the drug respect to SLN formulations,while at low ECN content the particle dimensions do not influence the release. In conclusions the results confirm the usefulness of SLN as carriers for topical administration and suggest the potentiallity of SLM for the delivery of drugs to the skin.