Effects of formulation and preparation method on drug entrapment of minoxidi niosomes

Abstract

Vesicular dosage forms are known to enhance drug penetration into and through the skin. A relatively new class of vesicular dosage forms, niosomes, is thought to be a good alternative for the costly and less stable phospholipid-based liposomes. This present study focused on the effects of formulation and processing factors on feasibility of niosome formation from commonly available non-ionic surfactants. Minoxidil was used as a model for drugs with borderline partition coefficients, which are usually cumbersome to formulate into a vesicular dosage form. Entrapment efficiency was used as a parameter to indicate the effects of formulation factors on the resultant niosomes. Niosome formulations were prepared by a method devoid of organic solvent. The results of the study indicated that it was feasible to prepare niosomes from Span®40, Span®60, and Brij®76 without use of organic solvent. However, cholesterol was required as an additive in all cases, but at different weight ratios. Total lipid concentration, presence of a stabilizer (either dicetylphosphate or Solulan®C24 at 5% by weight), and composition of the aqueous phase (pH and presence of propylene glycol as a co-solvent) affected feasibility of niosome formation as well as the entrapment efficiency. Equilibrating time also affected the entrapment efficiency of niosomes, depending on their membrane compositions. It was also possible to load minoxidil into blank niosomes by a continuous stir of blank niosomes with drug solution. The entrapment efficiency, however, was much lower than that obtained when the drug was included during the process of vesicle formation. The present study illustrates the role of formulation and processing factors on feasibility of niosome formation and on the entrapment efficiency of the resultant niosomes. These results could be used as a guideline for pharmaceutical scientists who wish to optimize a niosome delivery system for a drug with a borderline partition coefficient.