A comparison of indomethacin and diclofenac in the inhibition of experimental heterotopic new bone formation.

The effect of the two nonsteroidal antiinflammatory drugs Diclofenac and Indomethacin on the formation of heterotropic and orthotopic bone in rats was compared. Experimental heterotopic bone formation was induced by implanting demineralized bone matrix into the abdominal wall of rats. Indomethacin (3 mg/kg), Diclofenac (3, 6 or 12 mg/kg), or saline were given as daily subcutaneous injections. 3H-proline and 45Ca were given 24 h before the animals were killed. The net amount of bone formed by induction after three weeks was decreased by 15% by Indomethacin and Diclofenac in a dose of 3 mg/kg. The higher dose of 6 mg/kg of Diclofenac caused a higher degree of inhibition (30%), while 12 mg/kg produced toxic effects. Orthotopic bone was not affected by treatment with Indomethacin or Diclofenac. Although both drugs inhibit prostaglandin synthesis to a different degree, they exert similar effects on induced heterotopic bone, suggesting that this action is caused by an inhibition of the inflammatory response to trauma.