Failure of folic acid (pteroylglutamic acid) to affect hyperuricemia.

PGA administered in doses up to 1000 mg orally a day did not significantly lower the serum urate concentration nor decrease the urinary urate or total oxypurine excretion in five hyperuricemic subjects. The folate was well absorbed, as reflected by marked increases in the serum and erythrocyte folate concentrations, and up to 50% of the administered folate could be recovered in the urine. There was no evidence of clinical or laboratory toxicity at these high doses of folate. PGA is a weak inhibitor of human liver xanthine oxidase in vitro, and much of its inhibitory effect is secondary to trace contamination by pterin-6-aldehyde, a potent inhibitor of the enzyme.