Sustained antibacterial activity of doxycycline-loaded poly(D,L-lactide-co-glycolide) and poly(epsilon-caprolactone) nanoparticles.

Aim: To increase the entrapment efficiency of doxycycline (DXY)-loaded poly(D,L-lactide-co-glycolide) (PLGA):poly(epsilon-caprolactone) (PCL) nanoparticles by up to 70% by varying the different formulation parameters such as polymer ratio, amount of drug loading (w/w), solvent selection, electrolyte addition and pH in the formulation.

Method: Biodegradable polymers PLGA and PCL are used in various ratios for nanoparticle preparation using the water-in-oil-in-water double emulsion technique for water-soluble DXY. The physicochemical characterization of nanoparticles included size and surface charge measurement, study of surface morphology using scanning-electron microscopy, Fourier transform infrared spectroscopy study, differential scanning calorimetry analysis and in vitro release kinetics study.

Results: The mean particle size ranged from 230 to 360 nm, as measured by dynamic laser light scattering, and scanning-electron microscopy confirmed the spherical nature and smooth surface of the nanoparticles. Fourier transform infrared spectroscopy analysis of void nanoparticles, drug-loaded nanoparticles and native DXY indicated no interaction between the drug and polymer in the nanoparticle. Differential scanning calorimetry analysis of drug-loaded nanoparticles indicated a molecular level dispersion of DXY in the formulation. The antibacterial activity of native DXY and DXY-loaded nanoparticles were tested using a strain of Escherichia coli (DH5alpha) through growth inhibition and colony-counting method. The results indicated that DXY-loaded nanoparticles are more effective than native DXY due to the sustained release of DXY from nanoparticles in the E. coli strain.