Pirprofen

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Abstract
Synopsis: Pirprofen1 is a non-steroidal anti-inflammatory drug, related structurally to drugs such as ibuprofen, ketoprofen and naproxen. Published clinical trials indicate that pirprofen 600 to 1200 mg/day as 2 or 3 divided doses is a suitable alternative to usual therapeutic dosages of aspirin, flurbiprofen, ibuprofen, indomethacin, ketoprofen, naproxen, piroxicam and sulindac in the treatment of rheumatoid arthritis, osteoarthritis, ankylosing spondylitis, musculoskeletal disorders and non-articular rheumatism. More studies are required to evaluate its potential relative to other commonly used drugs in the treatment of gout, juvenile rheumatoid arthritis and dysmenorrhoea. In patients with acute postsurgical, trauma or cancer pain, single oral or intramuscular doses of pirprofen 200 to 400mg provide equivalent analgesic activity to usual therapeutic doses of aspirin, diflunisal, ketoprofen, noramidopyrine, paracetamol and pentazocine. As with other nonsteroidal anti-inflammatory drugs, gastrointestinal complaints are the most frequently reported side effects. At equivalent analgesic or anti-inflammatory dosages, pirprofen probably causes fewer side effects than aspirin and appears to be as well tolerated as the other agents with which it has been compared. Long term tolerability, particularly compared with some of the newer, purportedly less gastrotoxic agents or formulations, needs to be investigated further. Pirprofen does not appear likely to offer any particular advantage with respect to efficacy and tolerability over other non-steroidal anti-inflammatory drugs, except aspirin. However, as no one agent is the most suitable drug for all patients requiring such therapy, pirprofen may be considered along with other drugs of this type in the therapy of arthritic conditions and acute pain states. Pharmacodynamic Properties: In experimental animal models, pirprofen has been shown to possess anti-inflammatory, analgesic and antipyretic activities similar to those of several other non-steroidal anti-inflammatory drugs commonly used in the treatment of rheumatic conditions. The ulcerogenic activity of pirprofen in animals appears similar to that of diclofenac, flurbiprofen and indomethacin. The relative gastrointestinal toxicity compared with other non-steroidal anti-inflammatory drugs needs to be investigated further in animals and human subjects. Pirprofen inhibits the secondary phase of platelet aggregation induced by collagen and arachidonic acid in vitro but does not influence ADP-induced primary platelet aggregation in vitro or in vivo. Unlike aspirin whose effect is irreversible, pirprofen is a reversible inhibitor of prostaglandin synthetase in vitro and in vivo. It inhibits the cyclo-oxygenase but not the lipoxygenase pathway of arachidonic acid metabolism. Pirprofen is an inhibitor of leucocyte chemotaxis in vitro and in vivo in man, and it does not adversely affect cartilage in animal models of degenerative joint disease unlike certain other non-steroidal anti-inflammatory drugs. Pharmacokinetic Properties: Peak plasma concentrations of about 20 mg/L are attained about 1 to 1.5 hours after the oral ingestion of a 200mg dose of pirprofen in man; pharmacokinetics are linear over a dose range from 50 to 600mg. The rate of absorption is slowed by food or concomitant antacid administration, although the extent of absorption is unaffected. Steady-state plasma concentrations are achieved after 3 to 4 doses administered every 6 to 8 hours. The pharmacokinetics of pirprofen best fit a 2-compartment model: the total apparent volume of distribution is 8 to 12L, and that of the central compartment is 5L, where the drug is extensively bound (> 99.5%) to plasma proteins. Pirprofen diffuses into synovial fluid where relatively stable concentrations are maintained despite fluctuations in plasma concentration during repeated oral doses. The drug is extensively metabolised in the liver, and 11 metabolites have been identified in human urine. The major metabolites do not possess pharmacological activity. Unchanged drug and metabolites are excreted primarily as glucuronide conjugates in urine. 80% of a radiolabelled dose is excreted in urine and 8% in faeces over 24 hours. The elimination half-life is 6 to 7 hours and plasma clearance is 1.2 L/h. In patients with severe renal impairment, the half-life of pirprofen is prolonged to about 10 hours. Therapeutic Trials: In patients with rheumatoid arthritis and osteoarthritis, pirprofen 600 to 1200 mg/day is at least as effective and as well tolerated as aspirin 3600 mg/day, flurbiprofen 300 mg/day, ibuprofen 1200 mg/day, indomethacin 75 to 150 mg/day, ketoprofen 200 to 300 mg/day, naproxen 500 to 1000 mg/day, piroxicam 20 mg/day and sulindac 400 mg/day. Comparisons with aspirin were generally long term and demonstrated that pirprofen was better tolerated at equivalent anti-inflammatory dosages. Comparisons with other non-steroidal anti-inflammatory drugs were mainly of short duration (1 to 6 weeks). Longer term comparative trials are therefore required and, although unlikely to show differences in efficacy at optimal dosages, differences in relative tolerability might be revealed. In ankylosing spondylitis pirprofen 750 to 1000 mg/day appears as effective as indomethacin up to 125 mg/day and ketoprofen 300 mg/day. Open studies in patients with gout and juvenile rheumatoid arthritis have yielded encouraging results but comparative studies are required to determine the role of pirprofen in these conditions. Pirprofen 800 to 1200 mg/day is as effective as indomethacin 100 to 150 mg/day, ketoprofen 300 mg/day and piroxicam 20 mg/day in the short term (1 to 2 weeks) treatment of pain and inflammation associated with acute musculoskeletal disorders and non-articular rheumatism. Pirprofen 600 to 800 mg/day is effective in relieving pain and other symptoms associated with dysmenorrhoea but studies are required to determine its efficacy relative to other agents more commonly used in this condition. In moderate to severe pain (postsurgical, trauma, cancer), single oral doses of pirprofen 200 to 400mg are at least as effective as aspirin 650 to 900mg, diflunisal 500mg, ketoprofen 150mg, oxyphenbutazone 250mg, paracetamol 650mg, pentazocine 100mg and zomepirac 100mg. With intramuscular administration, a single dose of pirprofen 400mg is more effective in relieving pain than noramidopyrine 1000mg but less effective than pentazocine 60mg. Intramuscular pentazocine, however, produced more centrally mediated side effects such as nausea and vomiting. Side Effects: Pirprofen has been well tolerated in most patients to date. However, further data are required to determine its side effect profile more clearly in patients receiving long term therapy, particularly when compared with other frequently used non-steroidal anti-inflammatory drugs. The most frequent side effects are mild gastrointestinal complaints, followed less frequently by mild central nervous system and cutaneous effects. Both the frequency and nature of side effects appear similar to other non-steroidal anti-inflammatory drugs. Pirprofen is probably less likely to cause gastrointestinal effects and tinnitus than aspirin. It may produce fewer central nervous system effects than indomethacin, but tends to produce more gastrointestinal complaints. Pirprofen-induced hepatitis has been reported in several patients receiving long term therapy. Dosage: The usual starting dosage of pirprofen is 800 mg/day in 2 divided doses, and once improvement has occurred 600 mg/day may prove sufficient for maintenance therapy. An initial dosage of 1200 mg/day in 3 divided doses can be administered for 1 to 2 weeks in patients with rheumatoid arthritis or ankylosing spondylitis. For the relief of pain, the single dose is 200 to 400mg depending on pain severity up to a maximum of 1200 mg/day. Pirprofen 400mg can be administered intramuscularly for severe acute pain followed after several hours by another injection if necessary; once the pain has abated, the patient should be transferred to oral medication. The usual precautions and contraindications to non-steroidal anti-inflammatory drug therapy apply to pirprofen.