Biodistribution of mild analgesics.

1 Macro-autoradiographic methods were used to assess the biodistribution of [3H]-, or [14C]-acidic (aspirin, indomethacin, phenylbutazone) and non-acidic (antipyrine, aminopyrine, paracetamol) mild analgesics in rats with carrageenan-induced inflammation. 2 At anti-inflammatory doses all the acidic drugs (and/or their metabolites) were found to reach high concentrations in the stomach wall, liver, blood and bone marrow, kidney cortex and the inflamed tissue, that is, the tissues in which these drugs exert their therapeutic or side-effects. 3 In contrast, at analgesic doses, the non-acidic mild analgesics (and/or their metabolites) are equally distributed throughout the body with the exception of the gastro-intestinal lumen and the liver. This distribution pattern correlates well with the lack of acute side-effects and anti-inflammatory action of these drugs at therapeutic doses.