Thiosulphate and hydroxocobalamin prophylaxis in progressive cyanide poisoning in guinea-pigs.

The duration of action of the cyanide antidotes sodium thiosulphate and hydroxocobalamin was investigated in guinea-pigs after prophylactic administration before a long-term infusion of NaCN. The parameter for the diminution of the antidote action was the point of time at which the concentration of HCN in the exhaled air of the animals exceeded 100 nmol/kg per min. The time taken to reach this threshold level in the control animals was 12 min. While the threshold level could be extended only to 35 min with hydroxocobalamin (300 mg/kg i.v.) the protective action of sodium thiosulphate (100, 500 and 1000 mg/kg i.v.) persisted dose dependently for about 1, 2 and 4 h, respectively. Additionally we found a plasma half-life of sodium thiosulphate in guinea-pigs of 26 min. This value corresponds approximately to the plasma half-life of sodium thiosulphate in humans given in the literature. Because of the large injection volume necessary, sodium thiosulphate is not suitable for prophylactic use in man.