2, 3-Dimercaprol water-soluble analogs

When used in therapeutic doses, dimercaprol is associated with a high incidence of adverse effects, including hypertension, tachycardia, nausea, vomiting, lacrimation, salivation, fever (particularly in children), and pain at the injection site. Its use has also been associated with thrombocytopenia and increased prothrombin time—factors that may limit intramuscular injection because of the risk of hematoma formation at the injection site. Despite its protective effects in acutely intoxicated animals, dimercaprol may redistribute arsenic and mercury to the central nervous system, and it is not advocated for treatment of chronic poisoning. Water-soluble analogs of dimercaprol—unithiol and succimer—have higher therapeutic indices and have replaced dimercaprol in many settings. 

Two water-soluble analogs of dimercaprol have been studied as lewisite antidotes, namely meio-2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercapto- 1-propane sulfonic acid (DMPS) (see review by Aposhian, 1993). Their structures are as follows ... 

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