Vasodilator · Antihypertensive
Nitroprusside (Nipride)
Also called Nipride
Indications
- Immediate BP reduction in hypertensive crises
- Acute heart failure with high SVR, including acute mitral or aortic regurgitation
- Controlled hypotension to reduce surgical bleeding
- Aortic dissection, added after beta-blockade
- Pheochromocytoma crisis, with or after alpha-blockade
Dosing
Nitroprusside drip card and mL/h converterStart: 0.3–0.5 mcg/kg/min
Mechanism of action
Nitroprusside donates nitric oxide without enzymes: in red cells it reacts with oxyhemoglobin, releasing NO, forming methemoglobin and setting free its cyanide groups. NO activates soluble guanylyl cyclase in vascular smooth muscle, raising cGMP and lowering intracellular calcium, so arterioles and veins relax about equally. Because no enzymatic bioactivation is needed, nitrate-type tolerance does not develop; a rising dose requirement instead suggests cyanide toxicity.
Pharmacology
- Cardiovascular: balanced arterial and venous dilation cuts afterload and preload; output rises in failing hearts with high SVR
- Cardiovascular: reflex tachycardia; can steal coronary flow from ischemic areas
- CNS: cerebral vasodilation raises ICP and impairs autoregulation
- Respiratory: blunts hypoxic pulmonary vasoconstriction, raising shunt and lowering PaO₂
Pharmacokinetics
| Onset | Within 1–2 min |
|---|---|
| Duration | BP recovers 1–10 min after stopping |
| Half-life | Nitroprusside about 2 min; thiocyanate about 3 days, 2–3 times longer in kidney failure |
| Distribution | Roughly the extracellular space |
| Metabolism | Each molecule reacts with hemoglobin to give NO, one cyanmethemoglobin and four free cyanide ions; rhodanese then joins cyanide to thiosulfate, forming thiocyanate |
| Elimination | Thiocyanate in urine |
| Cyanide threshold | Above 2 mcg/kg/min cyanide forms faster than it is cleared; at 10 mcg/kg/min the body's buffer (about 175 mcg/kg) is used up in under 1 h |
| Organ failure | Kidney failure: thiocyanate accumulates (label: mean rate under 3 mcg/kg/min if eGFR under 30). Liver failure: less cyanide detoxification |
Chemistry
- Sodium nitroprusside, Na₂[Fe(CN)₅NO]·2H₂O (disodium pentacyanonitrosylferrate): a ferrous iron bound to five cyanide groups and one nitrosyl (NO⁺)
- Cyanide makes up about 44% of its weight
- An inorganic salt, water soluble and fully ionized
- Light breaks it down, releasing cyanide: cover the bag (not the tubing) with an opaque sleeve or foil; discard if it turns blue, green or bright red
- Vials (25 mg/mL) go in D5W only, stable 24 h if shielded; Nipride RTU comes ready in saline; no other drug in the line
Adverse effects and cautions
In the one-pagers
- Aortic Dissection and Hypertensive EmergencyAortic dissection: Beta-blocker FIRST (esmolol or labetalol), then a vasodilator (nicardipine, clevidipine or nitroprusside) if BP stays high
- Endocarditis and Valve EmergenciesValve emergencies: Papillary muscle rupture: Inferior MI, day 3–5; edema; v waves: Nitroprusside, IABP or Impella; surgery
- DKA and HHSInsulin deficiency, counter-regulation and ketones: Acetoacetate: Rises while BOHB is oxidized during treatment: Nitroprusside (urine or serum)
- Heart FailureDecompensated HF and shock: Warm-wet: Most common: IV loop diuretic; vasodilator (nitroglycerin, nitroprusside) if BP allows
- After Cardiac SurgeryHemodynamics, low output and vasoplegia: Afterload: hypertension strains suture lines and raises bleeding; use nicardipine, clevidipine or nitroprusside, or nitroglycerin when ischemia or radial spasm is the worry. After mitral repair for regurgitation the LV loses its low-pressure outlet into the atrium and tolerates afterload poorly.
- Endocrine EmergenciesPheochromocytoma crisis: Lower pressure with α-blockade or an arterial vasodilator: phentolamine 1–5 mg IV boluses or infusion, nicardipine, clevidipine or nitroprusside. Add esmolol for tachycardia only after α-blockade; labetalol alone is a poor choice because its IV β effect is about 7 times its α effect. Patients are volume-contracted, so expand volume as vessels relax. Catecholamine cardiomyo
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Sources
- FDA label: Nipride RTU (2018)
- FDA label: sodium nitroprusside injection, Mylan (2026)
For education and exam preparation only. Follow your institution’s protocols. Typical adult values for study. Follow the order, the label and your institution's protocols.