meso-2,3-dimercaptosuccinic acid ( dmsa , or succimer ) is an oral chelating agent for heavy - metal poisoning . while studying the urinary elimination of unaltered dmsa , altered dmsa ( i.e. , its mixed disulfides ) , and lead in children with lead poisoning , we observed a pattern of urinary drug elimination after meals suggestive of enterohepatic circulation . 
 the excretion of lead in urine patterned the elimination of altered dmsa rather than the parent molecule . 
 in addition , the half - life of elimination of dmsa via the kidney was positively associated with blood lead concentration . 
 two additional crossover studies of dmsa kinetics were conducted in normal adults to confirm the presence of enterohepatic circulation of dmsa after meals . in one , increases in plasma total dmsa concentration were observed after meals in all six subjects ; these increases were prevented by cholestyramine administration 4 , 8 , and 12 hr after dmsa . in the second 
 , the administration of neomycin also prevented increases in dmsa after meals . 
 these studies indicate that 1 ) a metabolite(s ) of dmsa undergoes enterohepatic circulation and that microflora are required for dmsa reentry ; 2 ) in children , moderate lead exposure impairs renal tubular drug elimination ; and 3 ) a metabolite of dmsa appears to be an active chelator.imagesfigure 1 . 
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