What is the Difference Between Nitroglycerin and Nitroprusside

The key difference between nitroglycerin and nitroprusside is that nitroglycerin predominantly dilates the epicardial coronary arteries by being converted to nitric oxide (NO) within the body, while nitroprusside dilates both large epicardial and small resistance arterioles by directly releasing nitric oxide.

Medications such as nitroglycerine and nitroprusside that vasodilate the coronary arteries are commonly used for coronary angiography and related intervention. Both these drugs exert their therapeutic effects by releasing nitric oxide, a potent vasodilating molecule, into the body. However, these compounds have distinct mechanisms of action and are employed in different clinical settings to address cardiovascular conditions. Nitroglycerin has a direct coronary effect and a peripheral hemodynamic effect. It primarily acts on the smooth muscles of blood vessels, resulting in their relaxation and widening. In contrast, nitroprusside produces a more balanced arterial and veinous vasodilation effect than nitroglycerin.

CONTENTS

1. Overview and Key Difference
2. What is Nitroglycerin 
3. What is Nitroprusside
4. Similarities – Nitroglycerin and Nitroprusside
5. Nitroglycerin vs. Nitroprusside in Tabular Form
6. Summary – Nitroglycerin vs Nitroprusside

What is Nitroglycerin?

Nitroglycerin or glyceryl trinitrate is a small molecular compound used to treat or prevent angina, congestive heart failure, hypertension, and anal fissures. It is an organic nitrate vasodilator that causes vasodilation in both arteries and veins. It has been used to treat angina since 1879. Sublingual administration for acute prophylaxis angina is the most common indication of nitroglycerin. In addition, transdermal and intravenous administrations are also available to treat several cardiac diseases. Furthermore, topical administration of nitroglycerine ointment is commonly used to treat anal fissures.

Nitroglycerin is rapidly absorbed upon sublingual administration, and around 60% of the drug is bound with plasma proteins. Mitochondrial aldehyde dehydrogenase 2 in the smooth muscle cells is responsible for the bioactivation of nitroglycerin. The metabolism of nitroglycerin ultimately results in nitro oxide (NO), a potent vasodilator that acts through the production of cyclic guanosine 3′,5′-monophosphate (cGMP).

What is Nitroprusside?

Nitroprusside is a direct-acting vasodilator primarily used to treat hypertension and manage acute heart failure. Therefore, it is often administered intravenously to manage hypertensive emergencies. Upon administration, nitroprusside dilates both peripheral arteries and veins in the vascular smooth muscle by producing NO. However, several studies have suggested that the effect of nitroprusside is more prominent in veins than in arteries.

Nitroprusside is a prodrug with ferrous iron complexed with NO and cyanide ions. Once the NO is released from the complex, it increases the intracellular cGMP to inhibit calcium entry into the cell, resulting in smooth muscle relaxation. Nitroprusside has a short half-life and reaches peak plasma concentration within 20 seconds after the intra-coronary bolus administration. The cyanides in the nitroprusside are metabolized to thiocyanate in the liver and eliminated via the kidney.

What are the Similarities Between Nitroglycerin and Nitroprusside?

• Nitroglycerin and nitroprusside have uses in managing cardiovascular conditions.
• They exert their therapeutic effects by inducing vasodilation.
• Both nitroglycerin and nitroprusside increase the nitric oxide (NO), a potent vasodilator, in the body.
• They have a rapid onset of action, making them useful when immediate vasodilation is required.
• Both have relatively short durations of action, allowing quick titration and adjustment of the therapeutic effect.

What is the Difference Between Nitroglycerin and Nitroprusside?

Nitroglycerine and nitroprusside are vasodilators commonly used to manage coronary angiography and related intervention. However, there is a distinct difference between nitroglycerine and nitroprusside. Nitroglycerin offers vasodilation by being converted to NO within the body, while nitroprusside directly releases NO to act as a direct-acting vasodilator. Nitroglycerin is primarily used to treat angina pectoris associated with coronary artery disease and congestive heart failure. In contrast, nitroprusside is typically used in hypertensive emergencies requiring rapid blood pressure reduction.

Nitroglycerin administration routes include sublingual, intracoronary, intraarterial, and intravenous, while nitroprusside is commonly administered as an intracoronary bolus or intravenous infusion. Common contraindications of nitroglycerin include hypotension, right ventricular infarction, and concurrent use of phosphodiesterase-5 inhibitors. In addition to hypotension and concurrent use of phosphodiesterase-5 inhibitors, nitroprusside is also contraindicated in hepatic failures and renal impairment.

Below is a summary of the difference between nitroglycerine and nitroprusside in tabular form for side-by-side comparison.

Summary – Nitroglycerin vs Nitroprusside

Nitroglycerine and nitroprusside are vasodilators used to manage coronary angiography and related intervention through NO-mediated vasodilation. Nitroglycerin-associated vasodilation is related to the conversion to NO within the body, while the nitroprusside-mediated effect is related to the immediate release of NO. Therefore, nitroglycerin is administered through sublingual, intracoronary, intraarterial, and intravenous routes to treat angina pectoris associated with coronary artery disease and congestive heart failure. In contrast, nitroprusside is commonly administered as an intracoronary bolus or intravenous infusion to treat hypertensive emergencies requiring rapid blood pressure reduction. Understanding this difference between nitroglycerine and nitroprusside is important in informed decision-making when managing patients undergoing coronary angiography and associated interventions.

Reference:

1. “Interventional Pharmacology-Vasodilators.” The Cardiology Advisor.
2. Fung, Ho-Leung. “Biochemical Mechanism of Nitroglycerin Action and Tolerance: Is This Old Mystery Solved?” Annual Review of Pharmacology and Toxicology, vol. 44, no. 1, 2004.

Image Courtesy:

1. “Nitroglycerin” By BartVL71 – Own work (Public Domain) via Commons Wikimedia
2. “Sodium-nitroprusside-2D” (Public Domain) via Commons Wikimedia