Polymeric colloidal systems containing ethionamide: preparation and physico-chemical characterization

The association of ethionamide with different colloidal systems was evaluated. Nanocapsules (NC), nanospheres (NS), and nanoemulsions (NE) were prepared by interfacial deposition and spontaneous emulsification techniques. Ethionamide was incorporated before (B) and after (A) preparation of nanoparticles. Ethionamide was assayed by HPLC, the particle size was determined using a Nanosizer, and the zeta potential using a Zetasizer 4. Free ethionamide was determined using a combined ultrafiltration-centrifugation technique. The drug release was determined by direct dilution of the nanoparticle dispersion in phosphate-buffer pH 7. All preparations retained acceptable particle size distribution (+/- 300 nm), except the NE. The zeta potential of all formulations was between -36.6 mV and -46.1 mV. Percentages of ethionamide associated were: NC (B: 62.4%, A: 56.2%), NS (B: 53.0%, A: 43.2%), and NE (B: 38.5%). After 45 days, the percentage of drug association with NC increased (B: 66.8%, A: 60.6%). The release profiles demonstrated that associated ethionamide was more readily released from the NC and NS prepared by procedure A rather than B. The ethionamide amount not released (B) was greater in NS than NC. The drug is mainly adsorbed onto the surface of nanoparticles. However, approximately 10% of ethionamide is encapsulated into NC and 20% entrapped into NS, respectively.