What is the appropriate initial dose and administration instructions for nitroglycerin (sublingual tablet) in a patient with angina pectoris or acute coronary syndrome?

Nitroglycerin Sublingual Tablet Dosing for Angina

Administer one sublingual nitroglycerin tablet (0.3-0.4 mg) immediately at the first sign of chest pain, dissolved under the tongue or in the buccal pouch. 1

Initial Dosing Protocol

• Take 1 tablet (0.3-0.4 mg) sublingually at the onset of chest discomfort 2, 3, 1
• The patient should rest, preferably in the sitting position during administration to minimize risk of orthostatic hypotension 1
• The dose may be repeated approximately every 5 minutes if pain persists 1, 3

Critical 5-Minute Decision Point

If chest pain is unimproved or worsening 5 minutes after the first dose, call 9-1-1 immediately to activate emergency medical services (EMS). 2, 3 This represents a significant change from the traditional "take 3 doses before calling" approach, as self-treatment with nitrates has been documented as a frequent cause of dangerous delays in patients with acute coronary syndrome. 2

Maximum Dosing Before Emergency Activation

• Maximum of 3 tablets in a 15-minute period (one every 5 minutes) 1, 3
• If pain persists after 3 tablets or if the pain is different than typically experienced, prompt medical attention is mandatory 1, 2
• While awaiting EMS arrival, patients tolerating nitroglycerin can take additional doses every 5 minutes up to the 3-dose maximum 2

Special Consideration for Chronic Stable Angina

For patients with known frequent angina and typical response patterns: 2

• If symptoms are significantly improved after 1 dose, it is appropriate to repeat nitroglycerin every 5 minutes for a maximum of 3 doses 2
• Call 9-1-1 if symptoms have not totally resolved after 3 doses 2, 3

Absolute Contraindications Before Each Dose

Do not administer nitroglycerin if: 2, 3, 1

• Systolic blood pressure is <90 mmHg or ≥30 mmHg below baseline 2, 3
• Patient has used phosphodiesterase-5 inhibitors (sildenafil, tadalafil, vardenafil) within the past 24-48 hours—this can cause catastrophic hypotension 1, 3
• Patient has signs of right ventricular infarction (especially with inferior wall MI)—these patients are preload-dependent and can experience life-threatening hypotension 3

Relative Contraindications and Cautions

Exercise caution if: 2, 3, 1

• Heart rate is <50 bpm (severe bradycardia) or >100 bpm (tachycardia) in the absence of heart failure 2, 3
• Patient is volume-depleted or already hypotensive 1
• Patient has hypertrophic cardiomyopathy, as nitrate therapy may aggravate angina 1

Prophylactic Use

• Nitroglycerin may be used prophylactically 5 to 10 minutes prior to activities that might precipitate an acute anginal attack 1

Hospital/Emergency Department Management

If pain persists after 3 sublingual doses: 2, 3

• Initiate intravenous nitroglycerin starting at 5-10 mcg/min (or 10-20 mcg/min per European guidelines), increasing by 5-10 mcg/min every 3-5 minutes until response, up to maximum 20 mcg/min 2, 3
• Obtain 12-lead ECG within 10 minutes to evaluate for STEMI or other ischemic changes 2, 3
• Administer aspirin 162-325 mg (chewed, non-enteric coated) if not already taken and no contraindications exist 2
• Continuous cardiac monitoring is essential 3

Common Pitfalls to Avoid

• Do not swallow the tablet—it must be dissolved sublingually or in the buccal pouch 1
• Do not delay calling 9-1-1 to complete all 3 doses first in patients with new or worsening symptoms 2
• Do not use someone else's nitroglycerin if the patient has not been previously prescribed it 2
• Do not rely on the burning/tingling sensation as a reliable indicator of tablet potency 1

Expected Side Effects

• Headache is common and may indicate drug activity 3, 1
• Hypotension and lightheadedness, especially upon standing after administration 3, 1
• Patients should use caution when returning to a standing position to prevent falls 1

Storage and Potency

• Keep nitroglycerin in the original glass container, tightly capped after each use to prevent loss of potency 1

Discharge Instructions

All patients post-ACS should receive: 2

• Sublingual or spray nitroglycerin with verbal and written instructions for use 2
• Clear instructions that initial angina lasting >1 minute should be treated with 1 dose; if not resolved in 3-5 minutes, call 9-1-1 immediately 2