Sodium thiosulphate decreases blood cyanide concentrations after the infusion of sodium nitroprusside

Plasma and red cell cyanide, and plasma thiocyanate, concentrations were measured in 30 patients undergoing elective nitroprusside-induced hypotension. One randomly selected group (n = 15), who received 0.21-0.70 mg kg-1 over periods of 50-160 min, were given a bolus of sodium thiosulphate 10.6-38.5 mg kg-1 immediately on cessation of the nitroprusside administration. The other group, who received infusions of 0.11-0.85 mg kg-1 for periods of 59-197 min, received no antidote. Cyanide concentrations, expressed as a percentage of the immediate post-infusion values, were significantly lower in the treated group in all subsequent blood samples (at 10, 30 and 60 min; plasma cyanide P less than 0.05; red cell cyanide P less than 0.001). Improved cyanide metabolism was further demonstrated by a sharp increase in mean plasma thiocyanate concentration (P less than 0.05) in the group receiving the antidote.