How is GTN (Glyceryl Trinitrate) administered to a patient with angina pectoris, considering potential cardiovascular disease and other health factors?

How GTN (Glyceryl Trinitrate/Nitroglycerin) is Administered

GTN is administered via three primary routes depending on clinical context: sublingual tablets (0.3-0.6 mg) or spray (0.4 mg) for acute angina relief, transdermal patches (0.2-0.8 mg/h) for chronic prophylaxis, or intravenous infusion (starting at 10 mcg/min) for unstable angina or acute coronary syndromes. 1, 2, 3

Sublingual Administration for Acute Angina

For acute anginal attacks, dissolve one sublingual tablet (0.3-0.6 mg) under the tongue or use one spray (0.4 mg) at the first sign of chest discomfort. 3, 4

Dosing Protocol:

• Patients should sit or lie down before administration to prevent orthostatic hypotension and falls. 4, 3
• Take the first dose immediately at symptom onset—do not wait to see if pain resolves on its own. 3, 4
• If symptoms persist after 5 minutes, call 9-1-1 immediately before taking a second dose. 4
• Maximum of 3 doses total, each separated by 5 minutes (total 15-minute period). 3, 4
• If chest pain persists after 3 doses or differs from typical angina, this indicates potential acute coronary syndrome requiring emergency evaluation. 4, 3

Prophylactic Use:

• Administer one dose 5-10 minutes before activities known to trigger angina (exercise, cold exposure, sexual activity). 3, 4, 1

Critical Administration Details:

• Do not chew, crush, or swallow sublingual tablets—they must dissolve under the tongue or in the buccal pouch. 3
• Keep tablets in the original glass container, tightly capped after each use to maintain potency. 3
• The burning/tingling sensation under the tongue is NOT a reliable indicator of tablet potency. 3

Intravenous Administration for Acute Coronary Syndromes

IV GTN is indicated for patients whose symptoms are not relieved after 3 sublingual doses, or for high-risk unstable angina/NSTEMI patients who are not hypotensive. 1, 2

Initial Setup and Titration:

• Start at 10 mcg/min via continuous infusion through non-absorbing tubing using an infusion pump. 1, 2, 5
• Increase by 10 mcg/min every 3-5 minutes until symptom relief or blood pressure response occurs. 1, 2, 5
• If no response at 20 mcg/min, continue with 10 mcg/min increments, then switch to 20 mcg/min increments at higher doses. 1, 5
• Once symptoms resolve, stop titrating—no need to continue increasing for blood pressure effect alone. 2, 5
• The commonly used ceiling is 200 mcg/min, though prolonged infusions at 300-400 mcg/min for 2-4 weeks have been safely administered without increasing methemoglobin levels. 1, 2, 5

Blood Pressure Parameters:

• Do NOT use if systolic BP <90 mmHg or >30 mmHg below baseline. 2, 5
• Target systolic BP: maintain ≥110 mmHg in normotensive patients. 2, 5
• In hypertensive patients, do not reduce mean arterial pressure by more than 25%. 2, 5

Tolerance Management:

• Tolerance develops after 24 hours of continuous infusion and is dose/duration dependent. 2, 5
• Transition to oral or topical nitrates within 24 hours once patient is stable and symptom-free for 12-24 hours. 2, 5
• For patients requiring IV GTN beyond 24 hours, periodic dose increases may be needed to maintain efficacy. 5
• Use graded reduction when discontinuing—abrupt cessation may cause rebound ischemia. 5

Transdermal Administration for Chronic Prophylaxis

Transdermal patches (0.2-0.8 mg/h) provide sustained nitrate delivery for angina prophylaxis, but require a nitrate-free interval to prevent tolerance. 1

Application Strategy:

• Apply patch in the morning and remove at bedtime to provide a 10-12 hour nitrate-free interval overnight. 6
• This intermittent regimen minimizes tolerance while optimizing nitrate sensitivity during daytime when angina attacks are most common. 6
• Continuous 24-hour application leads to tolerance in most patients with stable angina. 6

Absolute Contraindications (All Routes)

GTN is absolutely contraindicated in the following situations—administration can be fatal:

• Phosphodiesterase-5 inhibitor use: within 24 hours of sildenafil or 48 hours of tadalafil due to risk of profound hypotension, MI, and death. 1, 2, 4, 3
• Hypotension: systolic BP <90 mmHg or >30 mmHg below baseline. 2, 5, 3
• Right ventricular infarction: these patients depend critically on preload and GTN can cause cardiovascular collapse. 2
• Marked bradycardia or tachycardia. 2, 5
• Concurrent use with soluble guanylate cyclase stimulators. 3

Common Pitfalls to Avoid

• Patients taking tricyclic antidepressants or anticholinergics may have dry mouth that impairs sublingual tablet dissolution—consider using spray formulation or artificial saliva products. 3
• Avoid ergotamine and related drugs in patients using GTN, as ergotamine can precipitate angina. 3
• Headaches are common and may indicate drug activity—they can be managed with analgesics and often diminish with continued use. 3, 7
• Excessive use of sublingual GTN (scores of tablets daily for >10-12 hours) can lead to tolerance, though this is rare with appropriate use. 3
• IV GTN decreases the anticoagulant effect of heparin—monitor aPTT in patients receiving both medications. 3