Single dose pharmacokinetics of auranofin in rheumatoid arthritis

Six rheumatoid arthritis (RA) patients were given 2 6 mg doses of auranofin (AF) containing Au195, 6 months apart. The radioactivity in the whole body and in plasma, urine, and stool samples was measured for 6 months after each dose. Absorption was rapid with peak plasma concentrations occurring 1.2-2 h post administration. 195Au plasma half-lives (t1/2) ranged from 11.0-31.3 days, with 195Au detectable in plasma for about 80 days. Total body t1/2 averaged 69.2+/-29.7 days. Urinary excretion accounted for 15% of the dose. Cumulative stool excretion was 89%, although 72% was excreted in 10 days. Continued stool excretion over 6 months suggested a "central-enteric" component to the excretory route.