Pharmacokinetics of Oxicam Nonsteroidal Anti-Inflammatory Agents

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Oxicam nonsteroidal anti-inflammatory drugs (NSAIDs) are a group of structurally closely related substances with anti-inflammatory, analgesic and antipyretic activities. They have a weakly acidic character and are extensively bound to plasma proteins.

Piroxicam, the most widely used oxicam, is well absorbed after oral administration. Peak plasma concentrations (Cmax) of the drug are reached within 2 to 4 hours. Piroxicam has a small volume of distribution and a low plasma clearance. It undergoes hepatic metabolism and only 5 to 10% is excreted unchanged in urine. The elimination half-life varies between 30 and 70 hours. Age of the patient and renal or hepatic dysfunction do not seem to have any major effect on the pharmacokinetics of piroxicam. The drug reduces the renal excretion of lithium to a clinically significant extent, but the clinical significance of piroxicam-aspirin (acetylsalicylic-acid) and piroxicam-acenocoumarol interaction has not been established. Ampiroxicam, droxicam and pivoxicam are prodrugs of piroxicam that have been synthesised to reduce piroxicam-related gastrointestinal irritation. All prodrugs are well absorbed, but Cmax values are reached later than those following administration of piroxicam.

Tenoxicam is used in the management of rheumatic and inflammatory diseases. Mean Cmax values are achieved 2 hours postdose. Food reduces the rate but not the extent of absorption. The oral bioavailability of tenoxicam is 100% and rectal bioavailability is 80%. Like piroxicam, tenoxicam has a low volume of distribution and low plasma clearance. It is eliminated through hepatic metabolism. The mean elimination half-life is 60 to 75 hours. The pharmacokinetics of tenoxicam are independent of patient age, or concurrent liver or renal diseases. High doses of aspirin have been shown to increase the elimination of tenoxicam, but this has little clinical significance.

Isoxicam was in widespread clinical use until its worldwide marketing was suspended because of fatal skin reactions. Isoxicam is completely absorbed, but Cmax values are not reached until 10 hours postdose. It has a low plasma clearance, approximately 5 ml/min (0.3 L/h), and low volume of distribution. The mean elimination half-life is 30 hours and does not appear to be affected by the age of the patient. Isoxicam potentiated the anticoagulant effect of warfarin, necessitating a 20% dosage reduction.

Lornoxicam differs from other oxicam NSAIDs because it has a short elimination half-life of 3 to 4 hours. On the basis of limited data, some individuals seem to eliminate lornoxicam very slowly, suggesting the presence of polymorphic metabolism.

The pharmacokinetics of cinnoxicam and sudoxicam have not been studied thoroughly. However, like other oxicams, they appear to be absorbed completely after oral administration. Although the development of sudoxicam was stopped because of frequent adverse effects, this drug is interesting because, unlike other oxicams, its appears to have nonlinear elimination pharmacokinetics.

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