53. Thote, Amol J.; Chappell, John T., Jr.; Gupta, Ram B.; Kumar, Rajesh.  Reduction in the initial-burst release by surface crosslinking of PLGA microparticles containing hydrophilic or hydrophobic drugs.    Drug Development and Industrial Pharmacy  (2005),  31(1),  43-57.


Sustained-release approaches are emerging for the delivery of drugs from polymer encapsulation.  However, the most persistent problem that remains is the initial burst release of the drug, which can exceed the toxic limits.  Dexamethasone, a hydrophobic drug, was encapsulated in poly(lactide-co-glycolide) (PLGA) microparticles using the solvent evapn. method.  The drug release profile of these microparticles was studied and the initial burst was reduced by crosslinking of the microparticle surface using ethylene glycol dimethacrylate and tri(ethylene glycol) dimethacrylate.  Due to surface crosslinking, an addnl. diffusional resistance was created, which prevented easy dissoln. of the drug into the release medium and brought about a substantial redn. in the initial burst release.  Moreover, the time required for reaching a stationary-state release was also obsd. to be delayed, prolonging the sustained drug delivery.  This concept was further tested with a hydrophilic drug, the sodium salt of dexamethasone phosphate, encapsulated in PLGA polymer microparticles and was obsd. to reduce the burst release as well.  For synthesizing the polymer microparticles contg. dexamethasone, an o/w microemulsion and solvent evapn. technique was used; whereas, for those contg. dexamethasone phosphate, w/o/o/o phase sepn./coacervation technique was used.  The surface crosslinking was performed by UV radiation.


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