Comparative pharmacokinetics of parenteral and oral gold compounds.

The pharmacokinetics of intramuscular and oral gold compounds differ widely. Aurothioglucose and gold sodium thiomalate absorption is complete; 25% of auranofin (AF) is absorbed. Blood gold concentrations with conventional parenteral treatment generally peak between 600-800 microgram/dl the day of injection and decline gradually to about 300 micrograms/dl 7 days later. Levels range between 30 and 100 micrograms/dl, using 2-9 mg/d AF, and show little variation. A smaller percentage of gold is found in the cellular fraction of blood with I.M. than with oral gold. The blood half-life is approximately 6 days with gold sodium thiomalate, and 21 days with AF. Forty percent of the administered dose of injectable gold is excreted; depending upon dosage, 75-100% of oral gold is recovered in excreta, which is a combination of unabsorbed and excreted gold. Nearly 70% of parenteral gold is excreted in the urine and 30% in feces, while only 5% of AF is in urine and 95% in feces. The amount of gold retained following intravenous 195Au-labelled gold sodium thiomalate is 43% at 60 days and 25% at 250 days, but only 15% with oral radiolabeled AF 10 days after ingestion. Synovial fluid gold levels are much higher with parenteral than with oral gold but the blood-to-synovial fluid ratio is similar. Skin gold concentrations rise steadily with injectable but not oral treatment, but hair and nail accumulation is insignificant. Corneal, lens, and skin chrysiasis may develop with parenteral therapy, but has not been recognized with AF.