Monitoring toxicity in patients treated with nitroprusside
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Nitroprusside (Nipride) is a rapid-acting hypotensive agent used to treat hypertensive crisis and to produce controlled hypotension during surgery.
Nitroprusside reacts nonenzymatically with hemoglobin to produce 1 molecule of cyanomethemoglobin and 4 molecules of free cyanide, which are converted by hepatic rhodanese to thiocyanate. Toxicity can result from excessive cyanide production resulting in hypoxia and metabolic acidosis.
Accumulation of thiocyanate indicates that body stores of the reducing agent utilized by rhodanese to convert cyanide to thiocyanate may become depleted. In this situation, another antihypertensive drug should be considered.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
For nitroprusside therapy: < or =29 mcg/mL
Toxicity: >50 mcg/mL
Thiocyanate, the major detoxification product of cyanide, can also be present in smokers. Nonsmokers may have concentrations between 1 and 4 mcg/mL compared with smokers who may have concentrations between 3 and 12 mcg/mL.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
No significant cautionary statements
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
Burtis CA, Ashwood ER, Bruns DE: In Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Fifth Edition. Elsevier Health Sciences 2012 Oct 14