The effect of cimetidine on serum concentrations of piroxicam

Cimetidine does not alter the clearance or plasma binding of tenidap in healthy male volunteers

1. An open-label, placebo-controlled study was conducted to examine the effect of cimetidine on the steady-state pharmacokinetics of tenidap. 2. Twenty-four healthy volunteers received tenidap sodium (120 mg) each morning throughout the study. On day 14 plasma levels of tenidap had reached steady state; half of the subjects were treated concomitantly with cimetidine 800 mg at night, while the other half received placebo. Allocation of cimetidine or placebo was randomised. Plasma profiles of tenidap were measured on days 14 and 16. 3. The addition of cimetidine did not significantly affect the Cmax, tmax, or lambda z of tenidap. The AUC(0,24h) increased by 4% between days 14 and 16 in the cimetidine treatment group, compared with a decrease of 2% in the placebo group. This small difference is statistically significant (P = 0.047), but it is not considered to be clinically relevant. 4. It is concluded that concomitant administration of cimetidine does not significantly affect the pharmacokinetics of tenidap at steady state.

Pharmacokinetics of oxicam nonsteroidal anti-inflammatory agents

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.(ABSTRACT TRUNCATED AT 400 WORDS)

Interactions between non-steroidal anti-inflammatory drugs and H2-receptor antagonists or prostaglandin analogues

Published pharmacokinetic studies investigating possible interaction between H2-receptor antagonists (n = 22) or prostaglandin analogues (n = 6) and nonsteroidal anti-inflammatory drugs (NSAIDs) have been reviewed. With two exceptions the studies were carried out in young, healthy male volunteers rather than in arthritis patients. In addition some of the studies were poorly designed and inadequately described. Cimetidine appeared to increase the area under the plasma concentration-time curve, and hence to decrease the apparent oral clearance, of several NSAIDs including piroxicam, indomethacin, flurbiprofen, sulindac, oxaprozin and aspirin, while ranitidine co-administration resulted in similar changes for oxyprozin alone. The data currently available for prostaglandin analogues are insufficient to draw firm conclusions. It therefore remains a possibility that clinically relevant pharmacokinetic interactions may occur in elderly arthritic patients, and this issue needs to be addressed.

A lack of pharmacokinetic interaction between ranitidine and piroxicam

The effects of piroxicam (40 mg) on the pharmacokinetics of ranitidine (150 mg) and of ranitidine (150 mg bid) on the pharmacokinetics of piroxicam (20 mg) were assessed in two 2-way crossover studies in two groups of 18 healthy male subjects. In the first study there were no statistically significant differences between the pharmacokinetic variables for ranitidine in the presence or absence of piroxicam. The mean maximum plasma concentration (Cmax) was 467 ng.ml-1 for ranitidine alone and 466 ng.ml-1 in the presence of piroxicam: mean area under the plasma concentration vs time curve (AUC) was 2460 h.ng ml-1 and 2551 h.ng ml-1 respectively; and the mean terminal half-life (t 1/2) was 3.6 h and 3.8 h respectively. In the second study there were no statistically significant differences between the pharmacokinetic variables for piroxicam in the presence or absence of ranitidine. The mean Cmax was 2.1 micrograms.ml-1 in the presence of placebo and 2.0 micrograms.ml-1 in the presence of ranitidine respectively; mean AUC was 133 h.microgram ml-1 and 137 h.microgram ml-1 respectively, and the mean t 1/2 was 53.6 h and 54.5 h respectively.

Interactions of non-steroidal anti-inflammatory drugs

As NSAIDs are commonly used in patients receiving concomitant drug therapy, there is a risk of clinically significant drug interactions. Important interactions with NSAIDs involve one or both of two major mechanisms: pharmacokinetic (e.g. lithium, phenytoin and barbiturates) and pharmacodynamic (e.g. antihypertensive agents, diuretics). Prescription of a NSAID should be preceded by a careful evaluation of any coexisting pathology (such as renal dysfunction or hypertension) or concurrent drug therapy (such as anticonvulsant or anticoagulant agents) which may predispose a patient to the development of an interaction with potentially severe effects.

Review: interactions between H2-antagonists and non-steroidal anti-inflammatory drugs

Non-steroidal anti-inflammatory drugs (NSAIDs) are being prescribed increasingly with an H2-antagonist. This article reviews those published studies which have examined the potential for pharmacokinetic and, where appropriate, pharmacodynamic interactions between these classes of drugs. Studies involving the administration of a single dose of a NSAID to young healthy volunteers are of limited relevance in establishing the likely effect of an H2-antagonist on the blood concentrations of an NSAID in patients. Appropriate studies are those which will examine the effects of H2-antagonists on the steady-state pharmacokinetics of NSAIDs in patients with inflammatory joint diseases. More of such studies are required, particularly involving elderly patients.