Dimercaprol and dimercaptosuccinic acid are chelating agents that sequester the arsenic away from blood proteins and are used in treating acute arsenic poisoning.  The most important side effect is hypertension.  Dimercaprol is considerably more toxic than succimer. Dimercaptosuccinic acid monoesters, e.g. MiADMSA, are promising antidotes for arsenic poisoning.