Ethylenediaminetetraacetic acid (EDTA) and its analogues are all excellent chelates sequestering most metal ions, but for the same reason they are also not selective. EDTA coordinates preferentially to hard metal ions (Section 10.4.2) and due to the large chelate effect, quite stable complexes are formed. Since EDTA is inadequately absorbed only from the gastrointestinal tract, it is usually administered by intravenous injections. But due to the low degree of selectivity the hazard of eliminating essential metal ions is high. Adding the drug as Na2H2EDTA, the serum
concentration of calcium ions will be lowered, often with severe muscle spasms as a result. Instead, the CaH2EDTA salt is recommended, and in general the diet should be supplemented with essential metal ions during EDTA treatment.
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