How is nitro paste (nitroglycerin) used to manage angina pectoris?

Management of Angina Pectoris with Nitroglycerin Paste

Nitroglycerin paste (ointment) is effective for the prevention of angina pectoris but should be applied with a nitrate-free interval of 10-12 hours daily to prevent tolerance and maintain therapeutic efficacy. 1, 2

Mechanism of Action

Nitroglycerin paste works through several mechanisms:

• Venodilation: Reduces cardiac preload and ventricular wall tension
• Arterial vasodilation: Provides modest afterload reduction
• Coronary vasodilation: Improves blood flow to ischemic areas
• Antagonism of coronary vasospasm
• Increased collateral coronary flow

Dosage and Administration

Application Method

• Apply to non-hairy, clean, dry skin areas (typically chest, back, upper arm, or thigh)
• Use the applicator paper provided with the ointment
• Standard starting dose: 1/2 inch to 2 inches (1.3-5.1 cm) of ointment
• Spread over approximately 36 square inches (232 cm²) of skin 2
• Do not rub or massage the ointment into the skin
• Cover with plastic wrap or special applicator to prevent staining clothes

Dosing Schedule

• Critical: Implement a daily nitrate-free interval of 10-12 hours to prevent tolerance 1, 2
• Typical schedule: Apply in the morning and remove in the evening
• This allows for nitrate sensitivity during daytime hours when angina attacks are more common 3
• Continuous 24-hour application leads to complete loss of efficacy within 1 week 4

Clinical Efficacy

• Onset of action: 15-30 minutes after application 5
• Duration of effect: Up to 6-7 hours 1, 5
• Not suitable for aborting acute anginal episodes due to delayed onset 2
• Reduces frequency and severity of anginal attacks
• Increases exercise tolerance 1

Potential Side Effects

• Headache (most common)
• Flushing
• Hypotension
• Dizziness
• Reflex tachycardia (may cause "paradoxical" angina) 1

Important Precautions

1. Absolute contraindication: Concomitant use with phosphodiesterase-5 inhibitors 1, 6

   • Avoid within 24 hours of sildenafil/vardenafil
   • Avoid within 48 hours of tadalafil
   • Can cause profound, potentially fatal hypotension

2. Use with caution in:

   • Hypotension (SBP <90 mmHg)
   • Right ventricular infarction
   • Severe aortic stenosis
   • Hypertrophic cardiomyopathy

3. Monitoring:

   • Blood pressure should be monitored, especially when initiating therapy
   • An anginal attack not responding to nitroglycerin within 5 minutes may indicate myocardial infarction and requires immediate medical attention 1

Nitrate Tolerance Management

Tolerance is a major limitation of nitrate therapy that develops rapidly with continuous exposure:

• Tolerance begins within 24 hours of continuous application 7, 4
• Increasing the dose does not overcome tolerance 1
• A nitrate-free interval of 10-12 hours restores nitrate sensitivity 2, 7
• Remove the ointment at night and reapply in the morning 3

Place in Therapy

Nitroglycerin paste is part of a comprehensive approach to angina management:

• For prevention of angina attacks, not for acute relief
• Can be used alongside beta-blockers and calcium channel blockers for enhanced efficacy 6
• For acute angina episodes, sublingual nitroglycerin tablets or spray are preferred due to faster onset (2 minutes vs. 15-30 minutes) 8

By following these guidelines, particularly ensuring a daily nitrate-free interval, nitroglycerin paste can be an effective component in the management of stable angina pectoris, improving quality of life by reducing the frequency and severity of anginal episodes.