PLA stereocomplexes for controlled release of somatostatin analogue.

Reversible stereoselective complexes were spontaneously formed from mixing acetonitrile solutions of enantiomeric D-poly(lactide) (D-PLA), L-poly(lactide) (L-PLA), and octreotide (an octapeptide, somatostatin analogue). Hetero-stereocomplexes of poly (D-lactide) and L-octreotide were obtained by spray freezing of solution of D-PLA and octreotide. An additional transition temperature close to the melting point of enantiomeric PLA was observed in DSC thermogram. The same phenomenon was observed in stereocomplex of D-PLA/L-PLA and octreotide. The enthalpy of both transition temperatures correlate with peptide content in the hetero-stereocomplex. The spray method produced compact and smooth micro particles compared to particles formed by precipitation in acetonitrile solution. The particle size of stereocomplexes was in the range of 1.5 to 4 microm for all formations. Increasing peptide concentration in the stereocomplex increases the release rate of the peptide, and increases polymer degradation rate as monitored by lactic acid release form stereocomplexes.