How to administer Nitroglycerin (NTG) for angina symptoms?

How to Administer Nitroglycerin (NTG) for Angina

For acute angina, place one sublingual tablet (0.3-0.6 mg) under the tongue at the first sign of chest pain, repeat every 5 minutes for up to 3 doses total, and call 9-1-1 immediately if pain persists after the first dose or worsens. 1, 2

Sublingual Administration for Acute Angina

Initial Dosing

• Dissolve one tablet (0.3-0.6 mg) under the tongue or in the buccal pouch at the first sign of anginal attack 2
• Do not chew, crush, or swallow the tablet 2
• Patient should sit down during administration to prevent falls from lightheadedness or dizziness 2

Repeat Dosing Protocol

• If chest pain is unimproved or worsening 5 minutes after the first dose, call 9-1-1 immediately 1, 3
• While waiting for emergency services, repeat NTG every 5 minutes up to a maximum of 3 doses total 1, 2
• If pain persists after 3 tablets in a 15-minute period, or if the pain is different than typically experienced, this represents a medical emergency requiring immediate professional attention 3, 2

Important Distinction for Chronic Stable Angina Patients

The ACC/AHA guidelines make a critical distinction: for patients with known chronic stable angina whose symptoms are significantly improved after one dose, it is appropriate to repeat NTG every 5 minutes for up to 3 doses and call 9-1-1 only if symptoms have not totally resolved 1. However, this more permissive approach should only apply to patients with well-characterized, frequent angina patterns—not to new or worsening symptoms.

Prophylactic Use

• Administer 5-10 minutes prior to activities that might precipitate an acute attack 2
• This preemptive dosing can prevent exercise-induced angina 4

Critical Contraindications

• Absolute contraindication: Do not give NTG if patient has used sildenafil within 24 hours, tadalafil within 48 hours, or vardenafil (timing uncertain, but generally 24 hours) 1, 5
• These phosphodiesterase-5 inhibitors can cause profound hypotension, MI, and death when combined with nitrates 1, 5
• Avoid if systolic blood pressure <90 mmHg or >30 mmHg below baseline 1, 5
• Avoid with marked bradycardia or tachycardia 1, 5

Intravenous NTG for Refractory Angina

When to Initiate IV NTG

• For patients with persistent chest pain after 3 sublingual doses or ongoing refractory ischemic symptoms in the hospital setting 5, 3

IV Dosing Protocol

• Start at 10 mcg/min via continuous infusion through non-absorbing tubing 1, 5
• Increase by 10 mcg/min every 3-5 minutes until symptom relief or blood pressure response 1, 5
• If no response at 20 mcg/min, continue with 10 mcg/min increments, then switch to 20 mcg/min increments for more aggressive titration 1, 5
• Although a ceiling of 200 mcg/min is commonly used, doses up to 300-400 mcg/min have been shown to be safe and effective for optimal afterload reduction 5, 6
• Even prolonged infusion at 300-400 mcg/min for 2-4 weeks does not increase methemoglobin levels 1, 5

Blood Pressure Targets During IV Infusion

• Do not reduce systolic BP below 110 mmHg in previously normotensive patients 1, 5
• In hypertensive patients, do not reduce mean arterial pressure by more than 25% below baseline 1, 5

Tolerance Considerations

• Tolerance to hemodynamic effects typically develops after 24 hours of continuous therapy 1, 5, 7
• For patients requiring NTG beyond 24 hours, periodic dose increases may be needed to maintain efficacy 1, 5
• When patients are symptom-free for 12-24 hours, attempt to reduce IV dose and transition to oral/topical nitrates 1, 5

Alternative Formulations

NTG Spray

• Delivers 0.4 mg per spray, with similar efficacy to sublingual tablets 4
• Superior to sublingual tablets in patients with dry mouth, as it does not require saliva for dissolution 8
• Onset of action and duration similar to sublingual tablets 1

Long-Acting Nitrates (Oral/Transdermal)

• Acceptable for patients requiring chronic antianginal therapy but without ongoing refractory symptoms 1
• Use intermittent dosing strategies (12-14 hours on, 10-12 hours off) to prevent tolerance 1, 5, 7
• Transdermal patches ≥10 mg/24h provide effective nitrate effects but lose efficacy by 24 hours with continuous use 7

Common Pitfalls to Avoid

Patient Self-Medication Delays

• Self-treatment with NTG is a documented cause of delay in seeking emergency care 1
• Patients must understand that taking multiple NTG doses without calling 9-1-1 can worsen outcomes 1, 3

Storage and Potency

• Keep NTG in the original glass container, tightly capped after each use to prevent loss of potency 2
• The burning or tingling sensation under the tongue is NOT a reliable indicator of tablet potency 2

Drug Interactions

• Concomitant alcohol use may potentiate hypotension 2
• Tricyclic antidepressants and anticholinergics cause dry mouth, which may impair sublingual tablet dissolution—consider NTG spray in these patients 2, 8

Side Effects

• Headache is common and may indicate drug activity 2
• Hypotension-induced paradoxical bradycardia can worsen angina 2
• Excessive dosing can produce severe headaches 2