Influence of Surfactant on the Characteristics of W 1 /O/W 2 -Microparticles

The water-in-oil-in water (W 1 /O/W 2 ) double emulsion evaporation technique is widely used when the microencapsulation of soluble agents like naloxone HCl is intended. The present work shows the effect of HLB emulsifiers added to phase O on microsphere morphology, size, release, drug encapsulation efficiency. The addition of sorbitan ester to first emulsion (W 1 /O) and the HLB of the surfactant have an important effect on the characteristics of poly-lactide- co -glycolide (PLGA) microparticles (MP). This MP with sorbitan esters added were smaller and released the hydrophilic drug, naloxone, with no-significant difference at pH 5 versus pH 7.5 (phosphate medium). This is an important fact when long-drug release is considered since it is known that PLGA degradation leads to media acidification. The HLB value had an important effect on drug loading. Sorbitan monooleate led to the highest naloxone loading. Because of its low HLB (4.3), it is most suitable for stabilizing the W 1 /O emulsion, which is fundamental for the successful entrapment of a hydrophilic compound in MP prepared by double emulsion technique. Finally, drug solubility in the MP matrixes cannot be considered as a predictive parameter for drug encapsulation. Both surfactants increased the naloxone solubility in the polymer PLGA and only sorbitan monooleate increased the drug entrapment.