Chelation therapy is an antidote for poisoning by mercury, arsenic, and lead.  Chelating agents convert these metal ions into a chemically and biochemically inert form that can be excreted. Chelation using calcium disodium EDTA has been approved by the U.S. Food and Drug Administration (FDA) for serious cases of lead poisoning. It is not approved for treating "heavy metal toxicity". Although beneficial in cases of serious lead poisoning, use of disodium EDTA (edetate disodium) instead of calcium disodium EDTA has resulted in fatalities due to hypocalcemia. Disodium EDTA is not approved by the FDA for any use, and all FDA-approved chelation therapy products require a prescription.