GTN Tablet

Indications

Sublingual glyceryl trinitrate (GTN) is indicated for

• Acute angina or
• As angina prophylaxis
• Take 1 tablet 5 to 10 minutes before exercise or exertion to prevent an attack

Nonetheless, the prophylactic use of nitroglycerin is seldom emphasized to patients.

Method of Administration

Traditionally or as suggested in Garis Panduan Kaunseling Ubat-ubatan, patients should place 1 tablet under the tongue, every 5 minutes for up to 3 doses before calling the ambulance.

This approach has been shown to cause significant delay in obtaining immediate medical assistance.

• Hence, American College of Cardiology/American Heart Association (ACC/AHA) guideline recommends that for patients who are post–NSTE-ACS and have initial angina lasting more than 1 minute, nitroglycerin (1 dose sublingual or spray) is recommended; and if angina does not subside within 3 to 5 minutes, call 9-1-1 immediately to access emergency medical services.

Side Effect

The most common side-effect is headache.

• If it becomes troublesome, patient should seek medical attention.
• An interesting study in 2005 showed that GTN causes significantly more frequent headache episodes in patients with normal coronary arteries or minimal CAD than in patients with obstructive CAD (73% vs 23%, p<0.001).

Nitrate Tolerance

As we know, tolerance has been a major problem with the use of nitrates as chronic antianginal therapy. As suggested in Lexicomp, the administration of isosorbide dinitrate should not be around the clock, but to allow nitrate-free interval of at least 14 hours for immediate release products and at least 18 hours for sustained release products.

• Immediate release products: For twice daily dosing, consider administering at 8 am and 1 pm. For 3 times daily dosing, consider 8 am, 1 pm and 6 pm.
• Sustained release products: Consider once daily in morning or twice-daily dosing at 8 am and between 1 pm and 2 pm.

Hence, does long-term orally administered nitrates induce cross-tolerance to sublingual doses of nitroglycerin?

• An 1978 study has shown that cross-tolerance to the antianginal action of sublingually administered nitroglycerin is not resulted.

Storage

Not to forget, to remind patients that nitroglycerin tablets are both heat and light sensitive.

• It is important to store these tablets properly inside the original bottle away from moisture, heat and light.
• Do not carry them close to your body.

Once opened, they have a limited 8 weeks of shelf-life.

• If the sublingual GTN is potent, a slight tingling sensation should be felt under the tongue.

External Links

• Effects of long-term oral administration of isosorbide dinitrate on the antianginal response to nitroglycerin, 1978
  
• Delay in calling for help during myocardial infarction: reasons for the delay and subsequent pattern of accessing care, 2000