A water soluble biodegradable ABA- or BAB- type triblock polymer is disclosed that is made up of a major amount of a hydrophobic polymer made up of a poly(lactide-co-glycolide) copolymer or poly(lactide) polymer as the A-blocks and a minor amount of hydrophilic polyethylene glycol polymer B-block, having an overall weight average molecular weight of between about 2000 and 4990, and that possesses reverse thermal gelation properties. Effective concentrations of the triblock polymer and a drug may be uniformly contained in an aqueous phase to form a drug delivery composition. The release rate of the drug may be adjusted by changing various parameters such as hydrophobic/hydrophilic component content, polymer concentration, molecular weight and polydispersity of the triblock polymer. Because the triblock polymer is amphiphilic, it functions to increase the solubility and/or stability of drugs in the composition, as demonstrated by a phase diagram illustrating the gelation behaviour of aqueous solutions of a PLGA-PEG-PLGA triblock copolymer studied at different concentrations and temperatures.
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