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Decay of nitroprusside. I: In vitro
C J Vesey1, M Stringer, P V Cole
1Anaesthetics Laboratory, St Bartholomew's Hospital, West Smithfield, London.
British Journal of Anaesthesia
|June 1, 1990
Summary
Nitroprusside (SNP) decomposition in blood generates cyanide (HCN), contrary to prior beliefs. This reaction is temperature, pH, and time-dependent, occurring significantly within blood but not during standard assays.
Area of Science:
- Pharmacology
- Clinical Chemistry
- Toxicology
Background:
- Intravascular decomposition of sodium nitroprusside (SNP) was previously attributed to photolysis and assay artifacts, suggesting safe infusion if light is excluded.
- Concerns existed regarding the generation of cyanide (HCN) from SNP in vivo, impacting its safe clinical use.
Purpose of the Study:
- To investigate the true mechanism and conditions for cyanide (HCN) generation from sodium nitroprusside (SNP) in blood.
- To determine if SNP decomposition occurs in blood independently of light exposure or assay artifacts.
- To quantify the rate and factors influencing HCN release from SNP in a blood matrix.
Main Methods:
- Incubation of SNP with blood and plasma under varying conditions (temperature, pH, time).
- Measurement of HCN generated using a validated analytical method.
- UV spectrophotometry was employed to assess SNP concentration and distribution in plasma.
Main Results:
- HCN generation from SNP did not occur during standard analytical procedures.
- Significant HCN formation was observed exclusively after SNP incubation with blood.
- HCN release was dependent on temperature, pH (optimal around 7.5 in plasma), and incubation time, with 50% release at 37°C in blood occurring in 26.6 minutes and >90% yield within 2 hours.
- UV analysis indicated SNP primarily resides in plasma at clinically relevant concentrations.
Conclusions:
- Sodium nitroprusside (SNP) decomposition with cyanide (HCN) release is an intrinsic reaction with blood components, not an artifact of light or assay.
- The rate of HCN release is significantly influenced by physiological conditions within the blood.
- Understanding these decomposition kinetics is crucial for safe SNP administration and managing potential cyanide toxicity.
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