Inhibition of heterotopic osteogenesis in rats by a new bioerodible system for local delivery of indomethacin.

A study was done to evaluate the effect of a system for the local delivery of indomethacin on demineralized bone-induced formation of heterotopic bone in the abdominal muscles of rats. Two separate investigations were conducted on a total of forty-eight Wistar rats. In both series, two types of implants were used: polyorthoester and demineralized bone (Group A, the control group) and polyorthoester with 5 per cent indomethacin and demineralized bone (Group B, the experimental group). In the first series, host-tissue responses and osteoinduction were evaluated histologically at two, three, and four weeks after the implantation. In the second series, the formation of bone was quantified on the basis of uptake of 85Sr at four weeks after the implantation. The polyorthoester system for the local delivery of indomethacin significantly inhibited demineralized bone-induced heterotopic formation of bone, as demonstrated by light microscopy and by uptake of 85Sr. The polyorthoester, with or without the drug, caused little tissue reaction and was resorbed almost completely at four weeks.