Absorption and excretion of tolmetin in arthritic patients

The absorption, kinetics, biotransformation, and excretion of tolmetin and its metabolites were studied in patients with rheumatoid arthritis (RA) to evaluate the effects of the disease on tolmetin disposition. Five RA patients were stabilized on tolmetin sodium (300 mg, 4 times daily for 14 days) before receiving a single oral solution dose of tolmetin-14C sodium (300 mg as the acid) on day 15. Tolmetin was rapidly and completely absorbed (peak time, 20 to 60 min) and eliminated rapidly from plasma with a biphasic decay curve (t1/2beta congruent to 2.1 hr). MCPA, the oxidative metabolite, appeared more slowly (peak time, 40 to 90 min) but was eliminated rapidly in a biphasic manner (t1/2beta congruent to 1.7 hr). The terminal elimination phases for both tolmetin and MCPA demonstrated a curvature which suggested possible nonlinearity in the kinetic disposition of the drug. There were no apparent effects of the disease on the kinetics of tolmetin or MCPA. Tolmetin, MCPA, and tolmetin glucuronide were recovered quantitatively in urine (0 to 72 hr) with most of the exretion occurring in the 0- to 24-hr period. A significant increase, relative to data on normal subjects, in the renal clearance of both tolmetin and MCPA was noted. Concomitant increase in the apparent volume of distribution secondary to reported decreases in the plasma protein binding of tolmetin appeared to be the reason for increased renal clearance of tolmetin.