Hypotensive efficacy of a mixed solution of 0.1% sodium nitroprusside and 1% sodium thiosulphate

A mixed solution of 0.1% sodium nitroprusside and 1% sodium thiosulphate ('SNP-thiosulphate') was given as i.v. infusion to 80 patients, 30 of whom were hypertensive emergencies and 50 were surgical cases requiring induction of hypotension. This treatment lowered the blood pressure (BP) by an average of 30% of the initial levels in the hypertensive patients and 30-40% of the initial levels in the surgical patients. The mean effective dose in the hypertensive patients was 2.4 micrograms/kg/min compared with about 3 micrograms/kg/min in 40 cases treated with sodium nitroprusside as mono-infusion. For deliberate hypotension in surgical patients the mean doses of SNP, used here in the mixed infusion with thiosulphate, were 1.0 and 2.3 micrograms/kg/min, compared with 1.3-7.5 micrograms/kg/min in 181 patients treated with SNP as monotherapy. In contrast to conventional therapy with SNP, the infusion of SNP-thiosulphate even at extremely high dose rates did not produce toxic concentrations of prussic acid in the blood. In no case was a rise observed in the cellular enzymes as an indirect indication of hypoxic cell damage. SNP-thiosulphate is thus at least as effective at lowering BP as SNP infused alone, and has a substantially lower toxicity risk.