Nitroglycerin (Glyceryl Trinitrate)
Generic Name: Nitroglycerin (Glyceryl Trinitrate)
Therapeutic Class: Nitrate / Vasodilator / Anti-anginal
Indications
Nitroglycerin sublingual tablets are used for the acute management of coronary artery disease:
- Acute Angina Pectoris: Immediate relief of an ongoing attack of chest pain due to myocardial ischemia.
- Prophylaxis of Angina: Prevention of angina when taken 5 to 10 minutes before engaging in activities that might precipitate an attack (e.g., exercise, stress, or cold weather).
- Acute Left Ventricular Failure: Occasionally used in emergency settings to reduce cardiac preload.
Dosage & Administration
Strict adherence to administration technique is required for effectiveness.
- Acute Attack: Dissolve one tablet (usually 0.3 mg, 0.4 mg, or 0.6 mg) under the tongue or in the buccal pouch at the first sign of an acute anginal attack.
- Repeated Dosing: If symptoms are not relieved, the dose may be repeated every 5 minutes for a maximum of 3 doses.
- Emergency Protocol: If chest pain persists after 3 doses (15 minutes), the patient should seek immediate emergency medical attention (Call 999 or 911).
- Administration: Do not swallow or chew the tablet. The patient should sit down or lie down before taking the dose to avoid fainting due to sudden hypotension.
Description & Pharmacokinetics
Nitroglycerin is an organic nitrate that acts as a potent smooth muscle relaxant.
Mechanism of Action: Nitroglycerin is converted to **Nitric Oxide (NO)** in the vascular smooth muscle. NO activates guanylate cyclase, increasing **cyclic guanosine monophosphate (cGMP)**. This leads to the dephosphorylation of light chains of myosin, resulting in smooth muscle relaxation. Its primary effect is **Venodilation**, which reduces venous return to the heart (Preload reduction), and **Arterial dilation**, which reduces systemic vascular resistance (Afterload reduction). Together, these actions decrease myocardial oxygen demand.
Pharmacokinetics:
Mechanism of Action: Nitroglycerin is converted to **Nitric Oxide (NO)** in the vascular smooth muscle. NO activates guanylate cyclase, increasing **cyclic guanosine monophosphate (cGMP)**. This leads to the dephosphorylation of light chains of myosin, resulting in smooth muscle relaxation. Its primary effect is **Venodilation**, which reduces venous return to the heart (Preload reduction), and **Arterial dilation**, which reduces systemic vascular resistance (Afterload reduction). Together, these actions decrease myocardial oxygen demand.
Pharmacokinetics:
- Absorption: Rapidly absorbed through the sublingual mucosa, bypassing the liver (first-pass metabolism).
- Onset of Action: Extremely fast; effects are usually felt within 1 to 3 minutes.
- Metabolism: Rapidly metabolized in the liver by glutathione reductase.
- Duration: Short-acting, with effects lasting approximately 30 to 60 minutes.
Side Effects
- Headache: Most common (the "Nitrate Headache"), often severe but tends to decrease as therapy continues.
- Hypotension: Dizziness, lightheadedness, and orthostatic hypotension.
- Flushing: Redness of the face and neck.
- Tachycardia: Reflex increase in heart rate due to vasodilation.
- Syncope: Fainting, especially if the patient is standing or dehydrated.
Extra Important Information: Usage Insights
- PDE5 Inhibitors Warning: STRICT CONTRAINDICATION. Do not use if the patient has taken Sildenafil, Tadalafil, or Vardenafil within the last 24-48 hours. This can cause fatal hypotension.
- The "Tingle" Factor: A slight burning or tingling sensation under the tongue traditionally indicated potency, though this is not always a reliable marker for all modern formulations.
- Tolerance: Continuous exposure to nitrates can lead to tolerance. However, this is less common with the intermittent use of sublingual tablets compared to patches.
- Alcohol: Alcohol consumption can severely enhance the hypotensive effects of Nitroglycerin.
Pregnancy & Lactation
- Pregnancy: Category C. Use only if the potential benefit justifies the risk to the fetus.
- Lactation: It is not known if Nitroglycerin is excreted in human milk. Exercise caution when administering to a nursing woman.
Storage
CRITICAL STORAGE: Store in the original glass bottle. Nitroglycerin is highly volatile and can be absorbed by plastic. Keep the cap tightly closed. Protect from heat and light. Replace the supply every 6 months once opened.
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