The effect of concurrent aspirin upon plasma concentrations of tenoxicam

Effect of Uraemia and Anephric State on the Pharmacokinetics of Tenoxicam in the Rat

Renal alterations, uraemia and nephrotic syndrome induced in experimental animals caused a reduction in the plasma albumin concentration of 25 and 30%, respectively. As a result of this decrease, the unbound fraction of tenoxicam in uraemic rats (0·06 ± 0·02) and in anephric rats (0·11 ± 0·08) increased with respect to the control group (0·03±0·004). The induced hypoalbuminaemia did not modify the blood to plasma concentration ratio. Both plasma clearance (CL) and apparent volume of distribution at steady-state (Vdss) rose significantly with the increase in the unbound fraction: (Vdss 55 ±6 mL (control rats); 69 ± 12 mL (uraemic rats); 96 ± 30 mL (anephric rats); CL = 7± 1 mL h−1 (control rats); 12 ± 4 mL h−1 (uraemic rats); 15 ± 7 mL h−1 (anephric rats)). Tenoxicam elimination was found to be restrictive, with an extraction ratio less than 0·1 in the three groups. The induction of nephrotic syndrome was observed to have a significant effect on intrinsic metabolic activity, intrinsic clearance of tenoxicam being reduced by 30% in the anephric rats (161 ± 38 mL h−1) with respect to the values obtained in the control group (228 ± 22 mL h−1).

Fast RPLC-UV method on short sub-two microns particles packed column for the assay of tenoxicam in plasma samples

An extraction-less sample preparation technique followed by a RPLC-UV method on sub-two microns particles packed short column were used for the assay of tenoxicam in plasma samples. Protein precipitation was made by means of trichloroacetic acid addition. Supernatant was injected to the chromatographic column without any further pH adjustment. The mobile phase consisted in a mixture of acetonitrile and aqueous 0.1% phosphoric acid, at 2 mL/min flow rate and gradient elution. The Zorbax SB-C18 column (50 mm length, 4.6 mm internal diameter and 1.8 microm particle size) was thermostated at 60 degrees C. The mobile phase gradient composition program allowed separation of tenoxicam and piroxicam (internal standard), column clean-up and re-equilibration within 4 min. UV detection was achieved at 368+/-10 nm. The method is characterized by a low limit of quantitation of 25 ng/mL for tenoxicam, with a linearity interval up to 5500 ng/mL. The use of a low volume detection cell and detector high frequency data acquisition rate produced high precision and accuracy through a whole bioequivalence study of tenoxicam in two commercially available tablet formulations, after a single oral administration dose. Full method validation is presented. The high throughput characteristic of the proposed method allowed full validation and bioanalytical study completion within a 96 h period.

Tenoxicam pharmacokinetics in rats: a population model

This study was designed to establish the in vivo relationship between tenoxicam disposition and changes in plasma protein binding measured as an unbound fraction in plasma (fu). Tenoxicam was administered as a bolus 5-mg/kg dose, and total plasma concentrations, plasma albumin percentage, and fu were examined in five groups of rats (uremia or anephric states were experimentally induced in four groups to decrease plasma protein levels). Albumin levels were significantly decreased in all experimentally altered groups with respect to control animals (p < 0.01). A two-compartment population pharmacokinetic model that includes the effect of fu on the kinetic parameters was proposed to describe tenoxicam plasma concentration profiles. Plasma clearance (CL) increased but not proportionally with fu. Apparent volume of distribution of the central compartment (V) was linearly related to changes in fu and intercompartmental clearance was not affected by altered plasma protein binding. Expressing pharmacokinetic parameters as a function of fu resulted in a three- and five-fold decrease in the variability associated with CL and V, respectively.

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)

Clinical pharmacokinetics of tenoxicam

Tenoxicam is a nonsteroidal anti-inflammatory drug (NSAID) in the oxicam group. It is completely absorbed by the oral route and is about 99% protein bound in human plasma. Intake of food delays absorption without affecting bioavailability. There is no evidence for enterohepatic recycling of the drug in humans. Peak plasma concentrations of 2.7 mg/L (range 2.3 to 3.0 mg/L) have been reported in different groups of fasted healthy volunteers 1.9 hours (1.0 to 5.0 hours) after a single oral dose of 20mg. A mean elimination half-life of 67 hours (49 to 81 hours) has been estimated. Tenoxicam demonstrates linear single-dose pharmacokinetics over doses of 10 to 100mg. Because of its low lipophilicity and high degree of ionisation in blood (approximately 99%), the drug is poorly distributed to body tissues and is slowly taken up by hepatic cells. A small apparent volume of distribution of 9.6L (7.5 to 11.5L), and low total plasma clearance of 0.106 L/h (0.079 to 0.142 L/h), have been reported in different groups of healthy volunteers after oral and intravenous administration. Peak concentrations of tenoxicam in synovial fluid are less than one-third of those in plasma and they appear later, 20 hours (10 to 34 hours) after an oral dose. A parallel decrease in synovial fluid and plasma concentrations with time for both total and unbound tenoxicam has been reported. In vivo pH differences between synovial fluid and plasma in patients with rheumatoid arthritis may indicate significantly lower concentrations of unbound ionised tenoxicam in synovial fluid than in plasma. Data on relative binding capacities for tenoxicam in plasma and synovial fluid, and between different groups of individuals, are not conclusive. The protein binding of tenoxicam is pH dependent. The drug is almost entirely eliminated by liver metabolism. The 2 main metabolites, the inactive 5'-hydroxy and 6-O-glucuronidated forms, are excreted in urine and bile, respectively. The existence of additional metabolites in human bile has been suggested. Urinary excretion of the 5'-hydroxy metabolite decreases with reduced renal function. The 5'-hydroxy metabolite is detected in plasma in concentrations 1 to 5% of the parent compound and its decline parallels that of the parent compound (formation-rate limitation). Urinary and faecal excretion of unchanged tenoxicam is less than 1% of the administered dose. No significant amounts of unchanged tenoxicam are excreted in bile. Tenoxicam shows nearly linear pharmacokinetics during multiple-dose administration.(ABSTRACT TRUNCATED AT 400 WORDS)

Tenoxicam: acute dose-dependent disposition studies in rats

Single intravenous bolus doses of tenoxicam of 2.5, 5, and 10 mg/kg were administered to male Wistar rats to determine the effects of dose on tenoxicam pharmacokinetics. Predicted apparent volume of distribution at steady state (Vdss) and total plasma clearance (CL) were, respectively, 42 and 45% higher in the animals given 10-mg/kg dose than the animals given 2.5- and 5-mg/kg doses. Binding of tenoxicam to plasma proteins showed saturability, with a 33% higher unbound fraction of tenoxicam in plasma when total drug concentration in plasma was 36 mg/L (high dose group) in comparison with animals given the low doses (12 and 20 mg/L). The blood-to-plasma concentration ratio of tenoxicam was concentration independent and therefore did not account for the observed dose-dependent changes in Vdss and CL.

Intraocular and plasma kinetics of tenoxicam in rabbits

Non-steroidal anti-inflammatory drugs (NSAID) represent potentially useful agents in the treatment of a number of ocular pathologies, but their intraocular penetration and distribution have not yet been reported. With the aim of clarifying this point, we evaluated the concentrations of the well known NSAID, tenoxicam, in the aqueous and vitreous humors of rabbits treated i.m. with the drug (7 mg/kg). The tenoxicam kinetics in these ocular fluids followed that in plasma with the time-to-peak shifted to higher values in the vitreous (1 h) as compared to that in the aqueous and plasma (40 min). AUC was also higher in the vitreous (10.4 micrograms.h/ml) than in the aqueous humor (2.8 micrograms.h/ml).

The pharmacokinetics of total and unbound concentrations of tenoxicam in synovial fluid and plasma

Tenoxicam is a nonsteroidal antiinflammatory drug with an elimination half-life of 60-80 hours; it is administered once daily. Tenoxicam concentrations were measured in plasma (10 samples) and synovial fluid (6 samples) over a 24-hour dosage interval at steady state in 10 subjects with arthritis who had been taking the drug at a dosage of 20 mg/day for at least 2 weeks. Total tenoxicam concentrations in synovial fluid were always less than those in plasma, and there was little fluctuation in plasma or synovial concentrations over the dosage interval, although there was substantial inter-subject variation in both concentrations. There was a significant relationship between the tenoxicam dosage when expressed as mg/kg of body weight and the average steady-state total concentration of tenoxicam in plasma (r = 0.80, P = 0.006); this accounted for a substantial proportion of the intersubject variation. The mean +/- SD steady-state concentrations in synovial fluid and plasma were 3.9 +/- 1.8 micrograms/ml and 9.2 +/- 3.7 micrograms/ml, respectively, yielding a mean +/- SD synovial fluid: plasma ratio of 0.43 +/- 0.12. Synovial fluid:plasma ratios of total tenoxicam correlated with synovial fluid:plasma ratios of albumin (r = 0.71, P = 0.02). The synovial fluid:plasma ratio of unbound tenoxicam was 0.90 +/- 0.3 (95% confidence interval 0.68-1.11), which was not significantly different from a value of 1 (t = -1.09, P = 0.31).

Tenoxicam. An update of its pharmacology and therapeutic efficacy in rheumatic diseases

Tenoxicam administered orally, rectally or parenterally is an effective analgesic and anti-inflammatory agent for the symptomatic treatment of rheumatoid arthritis, osteoarthritis, ankylosing spondylitis and various rheumatic conditions such as tendinitis, bursitis, sciatica, back pain and gouty arthritis. In clinical trials its efficacy is at least equivalent to that of other NSAIDs and it is at least as well tolerated as piroxicam and probably better tolerated than diclofenac, indomethacin and ketoprofen. Compared with many other NSAIDs, tenoxicam offers certain advantages in that it is conveniently administered once daily and dosage adjustment is not required in the elderly or in patients with renal or hepatic impairment.

Pharmacokinetic drug interactions with nonsteroidal anti-inflammatory drugs

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most widely used drugs. Drug interactions with this class of compounds are frequently reported and can be pharmacokinetic and/or pharmacodynamic in nature. The pharmacokinetic interactions can be divided into 3 classes: (1) drugs affecting the pharmacokinetics of an NSAID. (2) an NSAID interfering with the pharmacokinetics of another NSAID and (3) NSAIDs altering the pharmacokinetics of another drug. Although the pharmacokinetics of some NSAIDs may be significantly affected by the concurrent administration of certain other drugs (including other NSAIDs), this type of interaction only occasionally leads to serious complications. Concurrent administration of antacids or sucralfate may delay the rate of oral absorption of NSAIDs but generally has little effect on the extent. Use of antacids increases urinary pH, leading to increased renal excretion of unchanged salicylic acid and decreased plasma concentrations of this antirheumatic agent. The H2-receptor blocking agent cimetidine inhibits the oxidative metabolism of many concurrently administered drugs, including certain NSAIDs. Probenecid inhibits the renal secretion of drug glucuronides and this will lead to accumulation in plasma of those NSAIDs eliminated primarily by the formation of labile acyl glucuronides such as naproxen, ketoprofen, indomethacin, carprofen. Cholestyramine decreases the oral absorption of many concurrently administered drugs, including NSAIDs. It may also decrease plasma concentrations of those NSAIDs undergoing enterohepatic circulation (e.g. piroxicam, tenoxicam) by interrupting the enterohepatic cycle. Corticosteroids stimulate the clearance of salicylic acid, leading to low plasma salicylate concentrations. Plasma concentrations of many NSAIDs are significantly reduced when the NSAID is coadministered with aspirin. The clinical relevance of most of these interactions is not well established. However, in those cases where the interaction results in elevated plasma concentrations of the NSAID, special caution should be exercised to avoid excessive accumulation of the NSAID especially in elderly and/or very sick patients who may be more sensitive to the more serious gastroduodenal and renal side-effects of these agents. By virtue of their pharmacokinetic and pharmacodynamic properties, NSAIDs may significantly affect the disposition kinetics of a number of other drugs. They can displace other drugs from their plasma protein binding sites, inhibit their metabolism or interfere with their renal excretion. If the affected drug has a narrow therapeutic index, the interaction may be clinically significant. The pyrazole NSAIDs (phenylbutazone, oxyphenbutazone, azapropazone) inhibit the metabolism of many drugs such as the coumarin anticoagulants, oral antidiabetics and anticonvulsants such as phenytoin. Salicylates displace oral anticoagulants from their plasma protein binding sites.(ABSTRACT TRUNCATED AT 400 WORDS)