Diclofenac oral bioavailability

Diclofenac is an exceedingly potent COX inhibitor slightly more efficacious against COX-2 than COX-1. Its absorption from the gastrointestinal tract varies according to the type of pharmaceutical formulation used. The oral bioavailability is only 30-80% due to a first-pass effect. Diclofenac is rapidly metabolised (hydroxylation and conjugation) and has a plasma half-life of 1.5 h. The metabolites are excreted renally and via the bile. 

In view of their incomplete oral bioavailability, several CYP2C substrates may undergo significant first-pass intestinal metabolism, including the CYP2C9 substrates verapamil (155), losartan (156), fluvastatin (157), and diclofenac (158), and the CYP2C19 substrates (5)-mephenytoin (159) and omeprazole... 

Pharmacokinetics The pharmacokinetics following oral administration of a single dose or multiple doses of diclofenac/misoprostol to healthy subjects under fasted conditions are similar to the pharmacokinetics of the 2 individual components. Food decreases the multiple-dose bioavailability profile of both formulations. 

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