An in situ gelling system for parenteral delivery

Polymer complexes formed by electrostatic interactions or hydrogen bonds between polymer strands can be utilized as a drug delivery system, as its ability to undergo a sol-gel transformation in response to changes in temperature, pH, and solvent concentration can lead to an in situ forming delivery system. A polymer complex of polyacrylic or polymethacrylic acid and polyethylene glycol, previously reported to be formed primarily by hydrogen bonds, is being investigated as such a system. Stable below pH less than or equal to 5.7, the complex is insoluble in water but dissolves in a hydroalcoholic solvent to yield a clear viscous solution. Upon injection, the diffusion of ethanol from the liquid transforms the system into a gel upon contact with physiological conditions. The gel disappears from the site with time due to dissociation of the complex. Water-soluble and low molecular weight, the dissociated components can be eliminated by glomerular filtration. Using a concentration of 50% ethanol as the cosolvent, the system can be injected by syringe. Thus, an interpolymer complex of polymethacrylic acid and polyethylene glycol may be utilized as a parenteral controlled-release drug delivery system.