MOBILIZATION OF HEAVY-METALS BY NEWER, THERAPEUTICALLY USEFUL CHELATING-AGENTS

Four chelating agents that have been used most commonly for the treatm ent of humans intoxicated with lead, mercury, arsenic or other heavy m etals and metalloids are reviewed as to their advantages, disadvantage s, metabolism and specificity. Of these, CaNa(2)EDTA and dimercaprol ( British anti-lewisite, BAL) are becoming outmoded and can be expected to be replaced by meso-2,3-dimercaptosuccinic acid (DMSA, succimer) fo r treatment of lead intoxication and by the sodium salt of 2,3-dimerca pto-1-propanesulfonic acid (DMPS, Dimaval(R)) for treating lead, mercu ry or arsenic intoxication, Meso-2,3-DMSA and DMPS are biotransformed differently in humans. More than 90% of the DMSA excreted in the urine is found in the form of a mixed disulfide in which each of the sulfur atoms of DMSA is in disulfide linkage with an L-cysteine molecule. Af ter DMPS administration, however, acyclic and cyclic disulfides of DMP S are found in the urine, The Dimaval-mercury challenge test holds gre at promise as a diagnostic test for mercury exposure, especially for l ow level mercurialism. Urinary mercury after Dimaval challenge may be a better biomarker of low level mercurialism than unchallenged urinary mercury excretion.