When to start Imdur (isosorbide mononitrate)?

When to Start Imdur (Isosorbide Mononitrate)

Start Imdur 30-60 mg once daily in the morning when patients with chronic coronary syndrome have inadequate symptom control despite initial treatment with beta-blockers and/or calcium channel blockers, or as part of initial therapy in patients who cannot tolerate these first-line agents. 1

Clinical Context for Initiation

Primary Indication: Chronic Coronary Syndrome (Angina)

• First-line therapy should be beta-blockers and/or calcium channel blockers for most patients with chronic coronary syndrome 1
• Add long-acting nitrates (including isosorbide mononitrate) when symptoms remain inadequately controlled on beta-blockers and/or calcium channel blockers 1
• Long-acting nitrates may be considered as initial treatment in patients with specific contraindications or intolerance to beta-blockers and calcium channel blockers 1
• Patients with coronary artery spasm are particularly appropriate candidates for nitrate therapy as initial treatment 1

Secondary Indication: Heart Failure with Reduced Ejection Fraction

• In self-identified Black or African American patients with NYHA class III-IV heart failure and LVEF ≤40%, start hydralazine/isosorbide dinitrate combination (not Imdur specifically) when already on ACE inhibitor/ARB/ARNI and beta-blocker therapy 1
• This is a different formulation (isosorbide dinitrate, not mononitrate) and different clinical context than angina management 1

Specific Dosing Algorithm

Starting Dose

• Begin with 30 mg once daily in the morning (given as single 30 mg tablet or half of 60 mg tablet) 2
• Alternative: 60 mg once daily can be used as initial dose 2
• The once-daily morning dosing provides antianginal protection for approximately 12 hours while allowing a nitrate-free interval to prevent tolerance 3, 4

Dose Titration

• After several days, increase to 120 mg once daily if needed (given as single 120 mg tablet or two 60 mg tablets) 2
• Rarely, 240 mg once daily may be required for refractory symptoms 2
• The 120-240 mg doses maintain statistical superiority over placebo during long-term treatment, whereas lower doses (30-60 mg) may lose efficacy over 6 weeks 5

Critical Timing Considerations

When NOT to Start Imdur

Absolute contraindications:

• Within 24 hours of sildenafil use (risk of profound hypotension) 3
• Within 48 hours of tadalafil use (risk of profound hypotension) 3
• Patients with hypertrophic cardiomyopathy 1
• Concurrent use with phosphodiesterase inhibitors 1, 6

Relative contraindications requiring caution:

• Right ventricular infarction - these patients depend on adequate RV preload, and nitrates can cause profound hypotension 3
• Inferior wall MI with RV involvement - exercise extreme caution 3
• Systolic blood pressure <100 mm Hg or symptomatic hypotension 1

Practical Implementation

Administration Instructions

• Take in the morning upon arising 2
• Do not chew or crush tablets - swallow whole with half-glass of fluid 2
• The extended-release formulation provides rapid onset (within 30 minutes) while maintaining 12-hour efficacy 7

Monitoring After Initiation

• Headache is the most common adverse effect, usually mild-to-moderate, improves with continued therapy, and rarely requires discontinuation 4, 8
• Monitor blood pressure after initiation and during titration 1
• Efficacy is generally observed 1-12 hours after administration 4

Common Pitfalls to Avoid

Tolerance Development

• The once-daily morning dosing of Imdur inherently prevents tolerance by providing a nitrate-free interval of at least 14 hours overnight 3, 4
• This is a key advantage over multiple-daily-dosing regimens with shorter-acting nitrates 8
• No evidence of classical tolerance develops with this dosing strategy 4, 8

Withdrawal Considerations

• Do not abruptly discontinue after long-term treatment - may exacerbate anginal symptoms 4, 9
• Some patients experience sudden deterioration requiring hospitalization upon abrupt withdrawal 9
• No rebound worsening of ischemia occurs at 24 hours (end of dosing interval), but withdrawal after chronic use is different 4, 5

Combination Therapy Cautions

• Do not combine with nicorandil (no additional efficacy) 6
• Safe to combine with beta-blockers - this combination provides superior antianginal protection compared to beta-blocker alone 8