Drug Information: Nitroprusside
Detailed information regarding Nitroprusside, a potent antihypertensive medication primarily used for the rapid reduction of blood pressure in hypertensive emergencies. Nitroprusside is a vasodilator that works by relaxing smooth muscle in blood vessels, leading to a decrease in systemic vascular resistance and blood pressure. It is administered intravenously and requires careful monitoring due to its rapid onset and potential for significant blood pressure reduction. It is metabolized to cyanide and thiocyanate, which can lead to toxicity with prolonged use or in patients with renal or hepatic impairment.
Category
Antihypertensive
Mechanism of Action
Nitroprusside acts as a direct vasodilator by releasing nitric oxide (NO). NO activates guanylate cyclase in vascular smooth muscle cells, increasing the production of cyclic GMP (cGMP). Elevated cGMP levels lead to the dephosphorylation of myosin light chains, inhibiting smooth muscle contraction and causing vasodilation. This vasodilation affects both arteries and veins, leading to a reduction in both preload and afterload, ultimately decreasing blood pressure. Because nitroprusside is light sensitive, infusions should be protected from light using an opaque covering to prevent degradation.
Clinical Uses
Nitroprusside is primarily used in hypertensive emergencies to rapidly lower blood pressure. It is also employed to control blood pressure during surgery, particularly in cases of aortic dissection or controlled hypotension to reduce bleeding. Furthermore, it can be used in the management of acute heart failure by reducing both preload and afterload, thereby improving cardiac output. Nitroprusside is sometimes used to treat severe mitral regurgitation and aortic stenosis where rapid reduction in afterload is beneficial. Careful monitoring of blood pressure is crucial during nitroprusside infusion to avoid precipitous drops in blood pressure, which can lead to end-organ ischemia.
Dosage
Adult Dosage: The typical initial dose is 0.3 mcg/kg/min intravenously, titrated to effect. The usual dose range is 0.3 to 10 mcg/kg/min. Blood pressure should be continuously monitored during administration. Maximum dose usually not to exceed 10 mcg/kg/min.
Pediatric Dosage: The initial dose is similar to adults, 0.3-1 mcg/kg/min intravenously, titrated to effect. Blood pressure should be continuously monitored.
Route of Administration: Intravenous infusion only. Nitroprusside solutions should be freshly prepared and protected from light.
Indications
* Hypertensive emergencies
* Controlled hypotension during surgery
* Acute heart failure
Contraindications
* Hypotension
* Compensatory hypertension (e.g., arteriovenous shunt or coarctation of the aorta)
* Inadequate cerebral circulation
* Patients with Leber’s hereditary optic neuropathy
* Use with phosphodiesterase-5 inhibitors (e.g., sildenafil, tadalafil)
* Severe renal or hepatic impairment (due to risk of cyanide and thiocyanate toxicity)
FAQ
Q: What is Nitroprusside used for?
A: Nitroprusside is used to rapidly lower blood pressure in hypertensive emergencies and to control blood pressure during surgery. It is also used in acute heart failure.
Q: How is Nitroprusside administered?
A: Nitroprusside is administered intravenously as a continuous infusion.
Q: What are the common side effects of Nitroprusside?
A: Common side effects include hypotension, reflex tachycardia, nausea, vomiting, and dizziness. Prolonged use can lead to cyanide toxicity and thiocyanate toxicity.
Q: How often should blood pressure be monitored during Nitroprusside infusion?
A: Blood pressure should be continuously monitored during Nitroprusside infusion due to its rapid onset and potential for significant blood pressure reduction.
Q: What is cyanide toxicity?
A: Cyanide toxicity is a potentially fatal condition that can occur with prolonged or high-dose Nitroprusside infusions, especially in patients with renal or hepatic impairment. Symptoms include metabolic acidosis, altered mental status, and seizures.
Q: Is Nitroprusside safe for pregnant women?
A: Nitroprusside should be used with caution during pregnancy, and only if the potential benefit justifies the potential risk to the fetus.
Q: What should I do if my blood pressure drops too low during Nitroprusside infusion?
A: The Nitroprusside infusion should be stopped or slowed down immediately. The patient may require fluid administration or vasopressors to raise blood pressure.
Q: How is Nitroprusside protected from light?
A: Nitroprusside solutions should be protected from light during preparation and administration by wrapping the IV bag and tubing in an opaque material, because it is light sensitive
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