Circulating thiomalate after administration of disodium aurothiomalate: impurity or active metabolite?

During studies of the metabolism of disodium aurothiomalate in patients with rheumatoid arthritis we have found that its pharmaceutical preparation. Myocrisin, contains 4 to 8% of free thiomalate. To establish whether the free thiomalate previously reported in plasma and urine of patients receiving Myocrisin is a true metabolite or results from this impurity, we prepared aurothiomalate containing 0.1% thiomalate. Intramuscular injection of the purified drug to 2 healthy subjects produced easily detectable levels of thiomalate in both plasma and urine; 7.7 and 9.8% respectively of the doses given were recovered in urine as free thomalate within 4 h. Thus, dissociation of disodium aurothiomalate does occur in vivo, releasing both gold and free thiomalate as potentially active forms.