The effect of a single oral dose of 500 mg naproxen on the synthesis in vivo of thromboxane A
2 and prostacyclin was studied in healthy volunteers. The synthesis of the prostanoids was assessed by measuring the urinary excretion of the metabolites 2,3-dinor-TxB
2 and 2,3-dinor-6-keto-PGF
1
, respectively, using stable isotope dilution assays based on gas chromatography — mass spectrometry.
Naproxen caused significant inhibition of the excretion of both metabolites for about two days. The reduction of the thromboxane metabolite was more pronounced (75% inhibition) than that of the prostacyclin metabolite (about 50% inhibition).
The data support the idea that naproxen causes reversible inhibition of cyclooxygenase.
Key words naproxen - thromboxane synthesis - prostacyclin synthesis - cyclooxygenase