Nitroprusside
Sodium nitroprusside is a potent, rapidly acting intravenous vasodilator used in veterinary critical care. Its effects on arterial and venous tone permit rapid adjustment of cardiac loading conditions and blood pressure. Major applications include severe hypertension and selected acute heart-failure presentations with high vascular resistance or refractory pulmonary congestion.
Group
Rapid-acting vasodilator
Mechanism of Action
Nitroprusside releases nitric oxide, which activates soluble guanylyl cyclase and increases cyclic GMP in vascular smooth muscle. Relaxation of both resistance and capacitance vessels reduces afterload and preload. The resulting changes can improve forward cardiac output and lower congestive pressures in responsive patients. Rapid onset and offset reflect its brief intravascular pharmacologic action.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Acute vasodilation | 1–5 mcg/kg/min | IV | Continuous | Titrate to blood pressure. Absolute reported rate ceiling is 10 mcg/kg/min; this is an infusion-rate limit, not a total dose cap. |
| Hypertensive crisis | 1–2 mcg/kg/min | IV | Continuous | Initial rate; titrate every 3-5 minutes. In crisis reports, reduce pressure approximately 25% over 4 hours, rather than abruptly. |
| Acute pulmonary edema | 0.5–10 mcg/kg/min | IV | Continuous | Alternative titration range; usually start 2 mcg/kg/min. Use dedicated infusion pump and BP monitoring. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Acute vasodilation | 1–5 mcg/kg/min | IV | Continuous | Titrate to blood pressure. Absolute reported rate ceiling is 10 mcg/kg/min; this is an infusion-rate limit, not a total dose cap. |
| Hypertensive crisis | 0.5 mcg/kg/min | IV | Continuous | Initial rate; titrate against continuous blood-pressure measurement. |
| Acute pulmonary edema | 1–2 mcg/kg/min | IV | Continuous | Separate feline protocol uses a 2 mcg/kg/min upper rate with systolic pressure above 90 mmHg; stop for hypotension. |
Indications
- Treatment of hypertensive emergencies in selected veterinary patients.
- Acute afterload and preload reduction in selected dogs or cats with severe congestive heart failure and adequate arterial pressure.
- Management of refractory cardiogenic pulmonary edema associated with excessive vascular resistance or severe valvular regurgitation.
Contraindications
- Hypotension
- Dehydration
Interactions
- Other vasodilators increase hypotension.
Adverse effects
- Hypotension, reflex tachycardia, cyanide toxicity and methemoglobinemia.
Toxicity
Cyanide risk increases above 5 mcg/kg/min; rates above 10 mcg/kg/min may provoke seizures. Sodium thiosulfate has been used for cyanide toxicity and methylene blue for methemoglobinemia. Stop or reduce infusion for profound hypotension. Prolonged/high exposure can cause cyanide or thiocyanate toxicity, especially with renal/hepatic impairment; metabolic acidosis or increasing rate requirement may be early clues. Continuous hemodynamic and acid-base assessment is essential.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Sodium nitroprusside injection 10 mg/mL | Injection | 10 mg / mL | IV |
| Sodium nitroprusside injection 25 mg/mL | Injection | 25 mg / mL | IV |
Monitoring and Administration
Continuously monitor blood pressure and heart rate; avoid pressure below 70 mmHg. Start near 2 mcg/kg/min and titrate in 1 mcg/kg/min increments.
Dilute 20-50 mg in 250 mL 5% dextrose to obtain 80-200 mcg/mL. Wrap infusion against light and discard discolored solution.
For 50 mcg/mL, dissolve a 50-mg vial in 2-3 mL 5% dextrose, then dilute to the stated final 1-L infusion. Protect solution from light, discard at 24 hours or if blue, dark red or green, and do not add other medicines. Use a dedicated pump; avoid extravasation and do not flush a running nitroprusside line into the patient.
Feline oxidative injury risk is greater. Some pulmonary-edema protocols maintain the effective rate for 12-15 hours, then wean while introducing oral therapy; longer protocols maintain up to 48 hours. Cyanide risk increases with prolonged exposure, especially beyond 3 days. Concurrent dobutamine is an individually managed separate infusion.