Pharmacology: Pharmacodynamics: Feldene is a nonsteroidal anti-inflammatory agent which also possesses analgesic and antipyretic properties. Edema, erythema, tissue proliferation, fever and pain can all be inhibited in laboratory animals by the administration of Feldene Flash. It is effective regardless of the etiology of the inflammation. While its mode of action is not fully understood, independent studies in vitro as well as in vivo have shown that piroxicam interacts at several steps in the immune and inflammation responses through: Inhibition of prostanoid synthesis, including prostaglandins, through a reversible inhibition of the cyclooxygenase enzyme; inhibition of neutrophil aggregation; inhibition of polymorphonuclear cell and monocyte migration to the area of inflammation; inhibition of lysosomal enzyme release from stimulated leucocytes; inhibition of superoxide anion generation by the neutrophil; and reduction of both systemic and synovial fluid rheumatoid factor production in patients with seropositive rheumatoid arthritis.
It is established that piroxicam does not act by pituitary-adrenal axis stimulation. In vitro studies have not revealed any negative effects on cartilage metabolism.
Pharmacokinetics: Absorption: Feldene Flash is well absorbed following oral administration. With food, there is a slight delay in the rate but not the extent of absorption following oral administration. Stable plasma concentrations are maintained throughout the day on a once-daily dosage. Continuous treatment with 20 mg daily for periods of 1 year produces similar blood levels to those seen once a steady state is first achieved.
Drug plasma concentrations are proportional for 20-mg doses and generally peak within 3-5 hrs after medication. A single 20-mg dose generally produces peak piroxicam plasma levels of 1.5-2 mcg/mL while maximum drug plasma concentrations, after repeated daily ingestion of piroxicam 20 mg, usually stabilize at 3-8 mcg/mL. Most patients have approximate steady-state plasma levels within 7-12 days.
Treatment with a loading dose regimen of 40 mg daily for the first 2 days followed by 20 mg daily thereafter allows a high percentage (approximately 76%) of steady-state levels to be achieved immediately following the 2nd dose. Steady-state levels, area under the curves and elimination half-life are similar to that following a 20 mg daily dose regimen.
Elimination/Biotransformation: Feldene Flash is extensively metabolized and <5% of the daily dose is excreted unchanged in urine and feces. One important metabolic pathway is hydroxylation of the pyridyl ring of the Feldene Flash side chain, followed by conjugation with glucuronic acid and urinary elimination. The plasma half-life is approximately 50 hrs in man.
Toxicology: Preclinical Safety Data: Subacute and chronic toxicity studies have been carried out in rats, mice, dogs and monkeys, using doses which ranged from 0.3-25 mg/kg daily. The latter dose is approximately 90 times the recommended human dose level. The only pathology seen was that characteristically associated with the animal toxicology of nonsteroidal anti-inflammatory agents eg, renal papillary necrosis and gastrointestinal lesions. With regards to the latter, the monkey proved to be quite resistant to this effect and the dog unusually sensitive.