P. Giunchedi et al., In vitro degradation study of polyester microspheres by a new HPLC method for monomer release determination, J CONTR REL, 56(1-3), 1998, pp. 53-62
Biodegradable polyesters have increasing importance as materials used for t
he preparation of microspheres. The knowledge of their degradation process
is important to prepare microparticulate delivery systems with suitable dru
g release rates. In this work an in vitro degradation study of empty and dr
ug loaded microspheres is described. Three different polyesters were used:
two poly-D,L-lactides of different molecular weight and a poly-D,L-lactide-
co-glycolide (50:50). Diazepam has been chosen as the model drug. Solvent e
vaporation and spray-drying were used as preparation methods. To study the
polymer degradation process, a new HPLC method is proposed for the direct a
nd (in the case of the copolymer) simultaneous determination of the monomer
(s): lactic acid (LA) and glycolic acid (GA). SEM and particle size analysi
s highlight the different characteristics of the particles, depending on th
eir preparation method: spray-dried spheres result to be always smaller wit
h respect to particles obtained by solvent evaporation. The results obtaine
d indicate in particular that: the preparation methods play an important ro
le in determining the degradation behaviour of microspheres, as unloaded sp
ray-dried particles are characterized by a higher monomer release fate with
respect to microspheres obtained by solvent evaporation; PLGA spheres degr
ade faster than PDLLA microparticles, according to the higher hydrophilicit
y of the copolymer; the two monomers are released at a different rate in th
e case of PLGA (faster for GA, slower for LA); the presence of diazepam inc
reases the polymer degradation rate, with respect to empty particles. (C) 1
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