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Pharmacology: Pharmacodynamics: Mechanism of action: Naproxen is a nonsteroidal anti-inflammatory drug (NSAID) that exhibits anti-inflammatory, analgesic and antipyretic activities. Naproxen inhibits synthesis of prostaglandins in body tissues by inhibiting cyclooxygenase; at least 2 isoenzymes, cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) have been identified that catalyze the formation of prostaglandins in the arachidonic acid pathway.
Pharmacokinetics: Naproxen is completely absorbed from the gastrointestinal tract. Oral bioavailability of naproxen is 95%. The peak plasma concentration of the drug occurs in 2-4 hours following oral administration. The volume of distribution of naproxen is 0.16 L/kg. Naproxen is more than 99% bound to plasma proteins. The drug crosses the placenta. Naproxen is also distributed into milk in concentrations of about 1% of simultaneous maternal plasma drug concentrations. The plasma half-life of naproxen is about 13 hours. Naproxen is extensively metabolized in the liver by cytochrome P-450 (CYP) isoenzymes 1A2 and 2C9 to 6-desmethylnaproxen. Approximately 95% of the drug is excreted in urine as unchanged naproxen (less than 1%) and 6-desmethylnaproxen (less than 1%) and their glucuronide or other conjugates (66-92%). Elimination of naproxen is reduced in patients with severe renal impairment. A small amount (less than 5%) of the drug is excreted in faces.
