Human pharmacokinetics of tolfenamic acid, a new anti-inflammatory agent

The pharmacokinetics of tolfenamic acid, a new anti-inflammatory agent was studied in six healthy volunteers after an intravenous dose of 100 mg and oral doses of 100, 200, 400 and 800 mg. The disposition of intravenous tolfenamic acid could be described by two-compartment open model, with a central compartment volume (Vdc) of 5.6 +/- 0.31 (mean +/- SE), volume during beta-phase (Vd beta) of 31 +/- 21, and a total elimination rate constant (k 10) 1.6 +/- 0.1 h-1. The terminal elimination half-life was 2.5 +/- 0.6 h and the total plasma clearance 155 +/- 15 ml/min. The elimination occurred principally by extrarenal mechanisms, the recovery of unchanged drug together with is glucuronide in urine averaging only 8.8% of the intravenous dose. The binding of tolfenamic acid to plasma proteins averaged 99.7%. The gastrointestinal absorption had a mean half-life of 1.7 +/- 0.1 h. Based on comparison of areas under the plasma concentration time-curves after intravenous and oral administration, the biovailability of tolfenamic acid capsules averaged 60%. The rate and extent of absorption and the rate of elimination of tolfenamic acid were independent of dose.