Piroxicam

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Abstract
Synopsis: Piroxicam1 is an N-heterocyclic carboxamide of 1,2 benzothiazine 1,1 dioxide with analgesic and anti-inflammatory activity. It has an extended half-life of about 40 hours and is suitable for once daily administration. Published studies indicate that piroxicam 20mg daily is comparable with aspirin 3 to 6g, indomethacin 75 to 150mg, phenylbutazone 400mg, naproxen 500mg, ibuprofen 1200 to 2400mg and diclofenac 75mg in rheumatoid arthritis. In osteoarthritis, piroxicam 20mg daily is comparable in efficacy with aspirin 2.6 to 3.9g, indomethacin 75mg, naproxen 500mg and fenbufen 600mg but is generally better tolerated than aspirin or indomethacin in patients with arthritic diseases. Piroxicam 20mg was at least as effective as indomethacin 75mg in a study in anyklosing spondylitis. As with other non-steroidal anti-inflammatory drugs gastrointestinal complaints are the most frequently reported side effects and their frequency and severity appears to be dose-related. Pharmacology: Piroxicam is a new non-steroidal analgesic and anti-inflammatory agent unrelated chemically to other available drugs. In nonspecific animal models of inflammation its potency (weight-for-weight) is similar to that of indomethacin. As an analgesic piroxicam is more potent (weight-for-weight) than aspirin, fenoprofen, ibuprofen, naproxen or phenylbutazone in inhibiting phenylquinone-induced writhing. In preliminary studies, piroxicam 20mg daily caused less faecal blood loss than aspirin 3.8g daily in humans. Piroxicam, like many other non-steroidal anti-inflammatory drugs, inhibits the secondary phase of platelet aggregation induced by adenosine diphosphate and col lagen-induced aggregation. In vitro and in vivo, piroxicam is an inhibitor of prostaglandin synthesis, being a selective reversible inhibitor of the cyclo-oxygenase step of arachidonic acid metabolism. Pharmacokinetics: Piroxicam is readily absorbed from the oral or rectal routes and reaches steady-state after about 7 days. After repeated doses of 20mg daily (the usual therapeutic dose) for 2 weeks, mean plasma concentrations 48 hours after the last dose are still within the therapeutic range. Piroxicam penetrates into the synovial fluid of patients with rheumatoid arthritis and attains concentrations about 40 % of those in plasma. On the basis of available data piroxicam appears to be extensively metabolised to inactive metabolites. The elimination half-life of piroxicam is extended due to a low clearance rate and has usually been calculated at around 38 hours in healthy subjects. Therapeutic Trials: In patients with rheumatoid arthritis piroxicam has been shown to be superior to placebo in practically all assessment criteria. Piroxicam 10mg twice daily was comparable with aspirin in maximum tolerated doses (2.65 to 6.3g daily) and 20mg once daily comparable with aloxiprin 4.8g daily. Studies comparing piroxicam with indomethacin, phenylbutazone and the phenylalkanoic or phenylacetic acid derivatives have generally indicated that piroxicam 20mg once daily or in divided doses, is comparable in efficacy with indomethacin 75 to 150mg, ibuprofen 1200mg daily, naproxen 500mg daily, diclofenac 75mg daily and phenylbutazone 400mg daily. As with other recently introduced non-steroidal drugs used in rheumatic diseases, piroxicam is better tolerated than aspirin, indomethacin or phenylbutazone. Long term open studies in rheumatoid arthritis have involved relatively small numbers of patients, but have shown that the drug maintains its effectiveness for periods of up to 2 years. These studies have also shown that prolonged administration of dosages of up to 40mg daily are poorly tolerated by the gastrointestinal tract. In patients with osteoarthritis, piroxicam 20mg daily appears to be at least as effective aspirin 2.6 to 3.9g daily, naproxen 500mg daily, or fenbufen 600mg at night and comparable with indomethacin 75mg daily in small numbers of patients. Long term studies in adequate numbers of patients demonstrated that the effectiveness of the drug is maintained without an increase in dosage and that at dosages of 20mg daily it is well tolerated by patients with osteoarthritis. A comparative trial indicates that piroxicam 20mg is an alternative to indomethacin 75mg in ankylosing spondylitis. Open trials in acute gout have been promising, but further comparative trials are necessary to determine the role of piroxicam relative to that of established drugs. In women with moderate to severe episiotomy pain, piroxicam 20 to 40mg was comparable with aspirin 648mg in providing pain relief. In acute musculoskeletal disorders doses of 40mg daily for the first 2 days, reducing to 20mg thereafter were comparable with phenylbutazone 600mg daily for 2 days and 300 to 400mg thereafter. Side Effects: The most frequently reported side effects have been gastrointestinal effects, but these have generally occurred less frequently with piroxicam than with therapeutically equivalent doses of aspirin, indomethacin or phenylbutazone. Peptic ulceration has occurred infrequently (1% overall incidence) at a dosage of 20mg daily, but has been 2 to 5 times more frequent at a dose of 40mg daily. Dosage: The usual initial and maintenance dose in rheumatoid arthritis and osteoarthritis is 20mg daily given as a single daily dose.

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