A
water soluble, biodegradable ABA- or BAB-type tri-block
polymer is disclosed that is made up of a major amount of a hydrophobic A
polymer block made of a
biodegradable polyester and a minor amount of a hydrophilic
polyethylene glycol(PEG) B
polymer block, having an overall average molecular weight of between about 2000 and 4990, and that possesses reverse thermal gelation properties. Effective concentrations of the tri-block polymer and a
drug may be uniformly contained in an aqueous phase to form a
drug delivery composition. At temperatures below the gelation temperature of the tri-block polymer the composition is a liquid and at temperatures at or above the gelation temperature the composition is a gel or semi-
solid. The composition may be administered to a warm-blooded animal as a liquid by parenteral, ocular, topical,
inhalation, transdermal, vaginal, transurethral, rectal, nasal, oral, pulmonary or aural delivery means and is a gel at body temperature. The composition may also be administered as a gel. The
drug is released at a controlled rate from the gel which biodegrades into non-toxic products. 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 tri-block polymer. Because the tri-block polymer is amphiphilic, it functions to increase the
solubility and / or stability of drugs in the composition.