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DESCRIPTION
Piroxicam capsules USP contain piroxicam which is a member of the oxicam group of non-steroidal anti-inflammatory drugs (NSAIDs). Each dark green and olive capsule contains 10 mg piroxicam, each dark green capsule contains 20 mg piroxicam for oral administration. The chemical name for piroxicam is 4-hydroxy-2-methyl-N-2-pyridinyl-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide. Members of the oxicam family are not carboxylic acids, but they are acidic by virtue of the enolic 4-hydroxy substituent. Piroxicam occurs as a white crystalline solid, sparingly soluble in water, dilute acid, and most organic solvents. It is slightly soluble in alcohol and in aqueous alkaline solutions. It exhibits a weakly acidic 4-hydroxy proton (pKa 5.1) and a weakly basic pyridyl nitrogen (pKa 1.8). It has the following structural formula:
C15H13N3O4S M.W. 331.35
Each capsule, for oral administration, contains 10 mg or 20 mg piroxicam. In addition, each capsule contains the following inactive ingredients: colloidal silicon dioxide, corn starch, D&C Yellow No. 10, FD&C Green No. 3, gelatin, lactose, magnesium stearate, povidone, sodium lauryl sulfate, and titanium dioxide.
Piroxicam capsules USP, 10 mg also contain: black iron oxide, FD&C Blue No. 1, and yellow iron oxide.
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CLINICAL PHARMACOLOGY
Pharmacodynamics
Piroxicam capsules are a non-steroidal anti-inflammatory drug (NSAID) that exhibits anti-inflammatory, analgesic, and antipyretic activities in animal models. The mechanism of action of piroxicam, like that of other NSAIDs, is not completely understood but may be related to prostaglandin synthetase inhibition.
Pharmacokinetics
Absorption
Piroxicam is well absorbed following oral administration. Drug plasma concentrations are proportional for 10 and 20 mg doses and generally peak within three to five hours after medication. The prolonged half-life (50 hours) results in the maintenance of relatively stable plasma concentrations throughout the day on once daily doses and to significant accumulation upon multiple dosing. A single 20 mg dose generally produces peak piroxicam plasma levels of 1.5 to 2 mcg/mL, while maximum drug plasma concentrations, after repeated daily ingestion of piroxicam capsules, 20 mg, usually stabilize at 3 to 8 mcg/mL. Most patients approximate steady- state plasma levels within 7 to 12 days. Higher levels, which approximate steady-state at two to three weeks, have been observed in patients in whom longer plasma half-lives of piroxicam occurred.
With food there is a slight delay in the rate but not the extent of absorption following oral administration. The concomitant administration of antacids (aluminum hydroxide or aluminum hydroxide with magnesium hydroxide) have been shown to have no effect on the plasma levels of orally administered piroxicam.
Distribution
The apparent volume of distribution of piroxicam is approximately 0.14 L/kg. Ninety-nine percent of plasma piroxicam is bound to plasma proteins. Piroxicam is excreted into human milk. The presence in breast milk has been determined during initial and long-term conditions (52 days). Piroxicam appeared in breast milk at about 1% to 3% of the maternal concentration. No accumulation of piroxicam occurred in milk relative to that in plasma during treatment.
Metabolism
Higher systemic exposure of piroxicam has been noted in subjects with CYP2C9 polymorphisms compared to normal metabolizer type subjects (see Pharmacogenetics and Special Populations, Poor Metabolizers of CYP2C9 Substrates).
Excretion
Piroxicam and its biotransformation products are excreted in urine and feces, with about twice as much appearing in the urine as in the feces. Approximately 5% of a piroxicam dose is excreted unchanged. The plasma half-life (Tfor piroxicam is approximately 50 hours.
Pharmacogenetics
CYP2C9 activity is reduced in individuals with genetic polymorphisms, such as the CYP2C9*2 and CYP2C9*3 polymorphisms. Limited data from one published report that included nine subjects each with heterozygous CYP2C9*1/*2 and CYP2C9*1/*3 genotypes and one subject with the homozygous CYP2C9*3/*3 genotype showed piroxicam systemic levels that were 1.7, 1.7 and 5.3 fold, respectively, higher compared to the 17 subjects with CYP2C9*1/*1 or normal metabolizer genotype. The pharmacokinetics of piroxicam have not been evaluated in subjects with other CYP2C9 polymorphisms, such as *5, *6, *9 and *11. It is estimated that the frequency of the homozygous *3/*3 genotype is 0.3% to 1.0% in various ethnic groups.
Special Populations
Pediatric
Piroxicam capsules have not been investigated in pediatric patients.
Race
Pharmacokinetic differences due to race have not been identified.
Hepatic Insufficiency
The effects of hepatic disease on piroxicam pharmacokinetics have not been established. However, a substantial portion of piroxicam elimination occurs by hepatic metabolism. Consequently, patients with hepatic disease may require reduced doses of piroxicam as compared to patients with normal hepatic function.
Poor Metabolizers of CYP2C9 Substrates
Patients who are known or suspected to be poor CYP2C9 metabolizers based on genotype or previous history/experience with other CYP2C9 substrates (such as warfarin and phenytoin) should be administered piroxicam with caution as they may have abnormally high plasma levels due to reduced metabolic clearance.
Renal Insufficiency
Piroxicam pharmacokinetics have been investigated in patients with renal insufficiency. Studies indicate patients with mild to moderate renal impairment may not require dosing adjustments. However, the pharmacokinetic properties of piroxicam in patients with severe renal insufficiency or those receiving hemodialysis are not known.
Other Information
In controlled clinical trials, the effectiveness of piroxicam has been established for both acute exacerbations and long-term management of rheumatoid arthritis and osteoarthritis.
The therapeutic effects of piroxicam are evident early in the treatment of both diseases with a progressive increase in response over several (8 to 12) weeks. Efficacy is seen in terms of pain relief and, when present, subsidence of inflammation.
Doses of 20 mg/day piroxicam display a therapeutic effect comparable to therapeutic doses of aspirin, with a lower incidence of minor gastrointestinal effects and tinnitus.
Piroxicam has been administered concomitantly with fixed doses of gold and corticosteroids. The existence of asteroid-sparingeffect has not been adequately studied to date.
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