Characterization of drug release from diltiazem-loaded polylactide microspheres prepared using sodium caseinate and whey protein as emulsifying agents

The influence of milk protein emulsifying agents on the characteristics, pa rticularly drug release, of polylactide microspheres was investigated. Dilt iazem loaded polylactide (PL) microspheres were successfully prepared using the dairy proteins, sodium casinate (SC) and whey protein isolate (WPI) as the emulsifying agents. Microspheres were characerized in terms of microsp here yield, electron microscopy, particle size, drug loading, DSC and XRD a nalysis and drug release. The yields of microspheres obtained were 53-63% a nd were independent of the emulsifying agent used. SEM revealed that, regar dless of the emulsifying agent employed, the microspheres were of good sphe ricity, but the surface appearance of the microspheres was not the same in all cases. The milk proteins resulted in microspheres approximately half th e size of those obtained with methylcellulose (MC). Significant differences in drug loading were observed between the three emulgents, the MC systems giving the highest values. Release profiles were sigmoidal in shape and wer e well fitted to the equation ln(x/1 - x = k . t - k . t(max), reflecting d egradation controlled drug release. The parameter k increased with drug loa ding, while tmax decreased. The relationships between the release parameter s [P. k and t(max))] and loading (L) could be quantified by equations of th e form P = a . L-N, N being negative in the case of tmax. Apart from the ef fect on loading efficiency, neither SC nor WPI appeared to significantly al ter drug release. The quantitative relationships observed in this study may have more general application in quantifying drug release from drug-polyme r composites at low loadings where polymer degradation controls drug releas e.