Some painkilling drugs may delay or even prevent the healing of fractures.

The main concern is the new generation of non-steroidal anti-inflammatory drugs (NSAIDs). Both drugs, Vioxx and Celebrex, are often used to ease the pain of broken bones.

But for over 20 years there have been occasional reports of impaired bone healing in patients taking NSAIDs. The issue may have escaped attention because the older generation of NSAIDS, such as ibuprofen and indomethacin, only appear to delay healing by a few weeks instead of blocking it. Interestingly, aspirin is one of the few NSAIDs that appears to kill pain without this side effect.

Ibuprofen and indomethacin delay bone healing by about one to two weeks in rats, which is the equivalent to slowing it down by 25 to 50 per cent in humans. None of the rats treated with Vioxx managed to heal their bones. In those treated with Celebrex, none managed to completely heal their bones but about half had some form of bone regrowth.

Traditional NSAIDs inhibit the enzymes cox-1 and cox-2. Cox-2 catalyses the production of hormone-like chemicals known as prostaglandins involved in inflammation, while cox-1 has a variety of roles not specific to the inflammatory response. Since the new generation of NSAIDs such as Celebrex block cox-2 almost exclusively, it was hoped they would have fewer side effects.

But it now seems that cox-2 may be crucial in helping bone-forming stem cells and growth factors do their work.

Journal of Bone and Mineral Research June, 2002 17:963