Comparative biochemical pharmacology of the oxicams.

The chronicity of the inflammatory process requires persistent tissue concentrations of non-steroidal anti-inflammatory drugs (NSAIDs), best achieved by using a drug with a long half-life as a once-daily regimen. The oxicams proved to be one of the most promising classes of NSAIDs. They have a similar molecular structure, though substitution of the benzothiazine ring by a thienothiazine system gives tenoxicam a more hydrophilic character. Tenoxicam is thus characterised by lower penetration into tissues requiring more lipophilic properties, e.g. the CNS and skin and, consequently, a lower incidence of adverse reactions at these target organs. Poor diffusion into hepatic cells--as a result of a small free fraction, tight binding to proteins and hydrophilic character--explains its low hepatic extraction ratio and--as a consequence--a long half-life. Compared to indomethacin and diclofenac, the oxicams have a moderate inhibitory activity on the synthesis and release of prostaglandins; tenoxicam is half as active as piroxicam, reflecting the correspondent difference in their steady-state plasma concentrations.