Sulfur donors cyanide poisoning

The metabolism of cyanide has been studied in animals. The proposed metabolic pathways shown in Figure 2-3 are (1) the major pathway, conversion to thiocyanate by either rhodanese or 3-mercapto-pyruvate sulfur transferase (2) conversion to 2-aminothiazoline-4-carboxylic acid (Wood and Cooley 1956) (3) incorporation into a 1-carbon metabolic pool (Boxer and Richards 1952) or (4) combining with hydroxocobalamin to form cyanocobalamin (vitamin B12) (Ansell and Lewis 1970). Thiocyanate has been shown to account for 60-80% of an administered cyanide dose (Blakley and Coop 1949 Wood and Cooley 1956) while 2-aminothiazoline-4-carboxylic acid accounts for about 15% of the dose (Wood and Cooley 1956). The conversion of cyanide to thiocyanate was first demonstrated in 1894. Conversion of cyanide to thiocyanate is enhanced when cyanide poisoning is treated by intravenous administration of a sulfur donor (Smith 1996 Way 1984). The sulfur donor must have a sulfane sulfur, a sulfur bonded to another sulfur (e.g., sodium thiosulfate). During conversion by rhodanese, a sulfur atom is transferred from the donor to the enzyme, forming a persulfide intermediate. The persulfide sulfur is then transferred... 

Patients who are critical and do not satisfactorily respond to supportive therapy should be administered specific cyanide antidotes as outlined in Table 19.5. Cyanide antidotes have been classified into three main groups based on their mechanism of action (1) methemoglobin inducers, (2) sulfur donors, and (3) cobalt compounds. The definitive treatment of cyanide poisoning differs in various countries due to different medical practices and guidelines. The safety... 

Sulfur donors for conversion of cyanide to thiocyanate by rhodanese or other sulfur transferases, that is, a source of sulfur. For moderate poisoning, sodium thiosulfate is the usual choice. 

I. Pharmacology. Sodium thiosulfate is a sulfur donor that promotes the conversion of cyanide to less toxic thiocyanate by the sulfur transferase enzyme rho-danese. Unlike nitrites, thiosulfate is essentially nontoxic and may be given empirically in suspected cyanide poisoning. 

Successful antidotes for acute cyanide poisoning are available. Sodium thiosulfate, a sulfur donor, can detoxify HCN by promoting its conversion to thiocyanate when catalyzed by the enzyme rhodanase (Baumeister et al., 1975 Egekeze and Oehme, 1980) however, the detoxification effect is slow. Another procedure utilizes cobalt compounds (hydroxoco-balamine) to bind directly with cyanide to form physiologically inactive cyanocobalamine (Offterdinger and Weger, 1969). 

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