Chelating agents cysteine

A recent paper by Harkness 101a) has done much to clarify the field. It was found that Zn2 chelating agents such as cysteine, EDTA, and o-phenanthroline (each 1 mil/) are all potent inactivators of crystalline placental phosphatase for instance, 15 min preincubation with 10 /Jl/ EDTA at pH 10.5 gave 95% inhibition. Full activity was immediately restored by addition of 100 fiM Zn2+ compared to only 25% recovery with Mg2. Preincubation of apophosphatase with 500 fiM Zn2+ gave a 30-fold increase in activity while the corresponding values for Mg2 and Co2 were 0.5 and 5-fold, respectively. 

Buffers can also be provided in parenteral formulations to ensure the required pH needed for solubility and/or stability considerations. Other excipients included in parenteral products are preservatives (e.g., benzyl alcohol, p-hydroxybenzoate esters, and phenol), antioxidants (e.g., ascorbic acid, sodium bisulfite, sodium metabisulfite, cysteine, and butyl hydroxy anisole), surfactants (e.g., polyoxyethylene sorbitan monooleate), and emulsifying agents (e.g., polysorbates). An inert gas (such as nitrogen) can also be used to enhance drug stability. Stability and solubility can also be enhanced by the addition of complexation and chelating agents such as the ethylenediaminetetraacetic acid salts. For a more detailed list of approved excipients in parenteral products, the reader should consult the monographs within the USP. 

Chelating agents for mercury, such as cysteine and penicillamine, have been used as intervention measures to reduce the concentration of inorganic mercury. However, chelation therapy has yielded variable success in cases of alkyl mercury poisoning. Studies of MMM suggest that chelators may reduce brain and blood mercury levels if started within a few days after exposure. Surgical gallbladder drains and oral administration of a nonabsorbable thiol resin have been applied in order to interrupt biliary excretion and reabsorption of mercury by the intestine. 

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