Two deadly misconceptions about nitroglycerin for chest pain and its correct usage

Nitroglycerin: Using nitroglycerin in this way during chest pain could be fatal: Dr. Zhou read a medical science article about how patients should use nitroglycerin for chest pain. The article stated that if a patient experiences chest pain at home, they should immediately place one nitroglycerin tablet under their tongue; if there is no relief after 5 minutes, take another tablet; if there is still no relief after another 5 minutes, take another tablet; if there is still no relief after 5 minutes, call 120 (emergency services) immediately.

There are two errors here:

1. Pay attention to the frequency of nitroglycerin administration. Nitroglycerin can dilate coronary arteries and improve myocardial ischemia. During an angina attack, sublingual administration can indeed provide rapid relief. Studies show that sublingual nitroglycerin takes effect in about 1 minute, reaches its maximum effect in 3-5 minutes, and its effect lasts for 10-30 minutes.

Although many articles suggest that if the patient does not respond to the first dose, they can take another tablet. If symptoms still do not improve after 15 minutes, it is recommended to seek medical attention. However, Dr. Zhou advises that if symptoms do not improve within 5 minutes of taking one nitroglycerin tablet sublingually, do not attempt to take a second tablet and immediately call 120 for emergency medical attention.

The reasons are: (1) An epidemiological study abroad showed that if a patient with angina pectoris experiences chest pain and nitroglycerin does not provide relief within 5 minutes, there is a 90% probability that the patient has already suffered an acute myocardial infarction; (2) Nitroglycerin takes effect rapidly, and if symptoms do not improve within 5 minutes of taking one tablet sublingually, the probability of relieving symptoms with another dose is very small. Therefore, time is of the essence; do not waste time waiting for symptoms to subside, seek medical attention promptly, and ensure your safety.

2. Do not take nitroglycerin immediately upon experiencing chest pain. Many patients with coronary heart disease, especially those with acute inferior myocardial infarction, often experience a drop in blood pressure or even cardiogenic shock. Taking nitroglycerin without knowing whether one's blood pressure is low may further lower blood pressure and worsen the condition. The correct approach is to measure blood pressure first when experiencing chest pain, provided a blood pressure monitor is available. If the blood pressure is not lower than 100/60 mmHg, sublingual nitroglycerin can be tried to avoid incorrect treatment and worsening of the condition.

Dr. Zhou will explain the precautions for using nitroglycerin in detail:

(1) Administration method: Nitroglycerin should be taken sublingually, not orally. Sublingual administration allows the drug to quickly enter the bloodstream through the sublingual vein. Oral administration means it will first be absorbed by the stomach and metabolized by the liver before entering the bloodstream, resulting in a slower onset of action. Additionally, some of the drug will be eliminated by the liver, reducing its effectiveness.

(2) The body position when taking nitroglycerin should be semi-recumbent. Avoid rapid changes in body position after taking the medication to prevent orthostatic hypotension.

In conclusion, nitroglycerin is indeed a very effective drug for relieving angina, but incorrect use can sometimes have the opposite effect. Patients should be aware of this.