From the Guidelines
Nitroglycerin (glyceryl trinitrate) itself rapidly relieves anginal pain in a 50-year-old man by reducing myocardial oxygen demand and enhancing myocardial oxygen delivery through vasodilation of both coronary and peripheral blood vessels.
Mechanism of Action
The mechanism by which nitroglycerin relieves anginal pain involves the relaxation of vascular smooth muscle, leading to vasodilation. This effect decreases cardiac preload and afterload, which in turn reduces myocardial oxygen demand. Simultaneously, nitroglycerin improves coronary blood flow to ischemic areas, further contributing to the relief of anginal pain 1.
Administration and Dosage
When experiencing chest pain, the patient should place one sublingual nitroglycerin tablet (0.3-0.6 mg) under the tongue and allow it to dissolve. Relief typically occurs within 1-5 minutes, but according to the most recent guidelines, rapid relief within 1 or 2 minutes is expected 1. If pain persists, the dose can be repeated at 5-minute intervals, up to a maximum of three tablets over 15 minutes.
Important Considerations
If chest pain continues after three doses, the patient should seek emergency medical attention immediately as this may indicate a heart attack. It is also crucial for the patient to sit or lie down when taking nitroglycerin to prevent falls from potential lightheadedness. Nitroglycerin tablets should be stored in their original container, away from heat and moisture, and replaced every 3-6 months as they lose potency over time.
Side Effects and Precautions
Side effects may include headache, dizziness, and hypotension. Patients should be aware of these potential side effects and take necessary precautions to avoid injury. The use of nitroglycerin is contraindicated in certain situations, such as after the use of phosphodiesterase inhibitors like sildenafil, due to the risk of profound hypotension 1.
Clinical Guidelines
Clinical guidelines emphasize the importance of patient education on the use of nitroglycerin for anginal pain relief, including the proper dosage, administration, and potential side effects. Patients at high risk for acute coronary syndromes should be instructed to call emergency services immediately if symptoms persist or worsen despite nitroglycerin use 1.
From the FDA Drug Label
Nitroglycerin is a type of medicine known as an organic nitrate and is a vasodilating agent. It is used to treat a type of chest pain called angina. Nitroglycerin sublingual tablets can relieve this pain. One tablet should be dissolved under the tongue or in the buccal pouch at the first sign of an acute anginal attack. The dose may be repeated approximately every 5 minutes until relief is obtained.
The pain is rapidly relieved because nitroglycerin acts as a vasodilating agent, which means it widens the blood vessels, allowing more blood to flow to the heart and relieving the anginal pain 2, 2.
- Vasodilation reduces the workload of the heart, decreasing the oxygen demand, and thus relieving the pain.
- Nitroglycerin is specifically used to treat angina, which is a type of chest pain that occurs when the heart does not get enough blood.
From the Research
Mechanism of Action of Nitroglycerin
The rapid relief of anginal pain in a 50-year-old man taking nitroglycerin can be attributed to several mechanisms:
- Nitroglycerin causes both arterial and venous smooth muscle dilation by the intracellular release of nitric oxide, which activates guanylate cyclase, resulting in an accumulation of cyclic GMP 3.
- The decrease in myocardial oxygen consumption is likely due to a reduction in preload, which can decrease arterial wall tension and improve coronary blood flow 3, 4.
- Nitroglycerin also has direct coronary circulatory actions, including epicardial coronary artery dilation, prevention of coronary vasoconstriction, enhanced collateral flow, and coronary stenosis enlargement 4.
- The administration of nitroglycerin causes changes in the systemic and coronary circulation that combine to reduce myocardial oxygen demand and to increase supply, thereby attenuating exercise-induced ischemia 5.
Effects on Myocardial Oxygen Demand and Supply
The relief of anginal pain can also be attributed to:
- A decrease in afterload (aortic pressure) and myocardial oxygen demand, as well as an increase in myocardial oxygen supply (Buckberg index) 5.
- A reduction in cardiac work due to venodilation and arterial relaxation, resulting in a decrease in intracardiac chamber size and pressures 4.
- The prevention of distal coronary artery or collateral vasoconstriction, which can reduce blood flow downstream from a total coronary obstruction 4.
Clinical Implications
The use of nitroglycerin in the treatment of angina pectoris is supported by its ability to rapidly relieve anginal pain and improve myocardial oxygen supply 3, 4, 5. The administration of nitroglycerin should be done with caution, especially in patients with acute pneumonia, as it may cause a decrease in arterial oxygen tension (PaO2) 6.