Generic Name

Imdur

Brand Names

for isosorbide mononitrate (IMN), a *nitrate* vasodilator.

Mechanism

Imdur is the brand name for isosorbide mononitrate (IMN), a *nitrate* vasodilator.
• Release & Metabolism: Oral IMN is rapidly hydrolyzed to isosorbide dinitrate and subsequently to nitric oxide (NO) in the bloodstream.
• NO Pathway: NO activates soluble guanylate cyclase → ↑ cyclic‑guanosine monophosphate (cGMP) → dephosphorylation of myosin light chains → smooth‑muscle relaxation.
• Vascular Effects: Predominant venous dilation reduces preload; at higher doses arterial dilation decreases afterload.
• Result: Decreased myocardial oxygen demand and relief of anginal pain.

Pharmacokinetics

Indications

• Stable angina pectoris – prophylaxis and symptom control.
• Pre‑operative angina prophylaxis (short‑term).
• Short‑acting sublingual form (Imdur® Rapid) for acute anginal attacks (≤30 min onset).

Contraindications

• Absolute Contraindications
• Severe hypotension (SBP <90 mm Hg).
• Known hypersensitivity to nitrates.
• Concomitant use of phosphodiesterase‑5 inhibitors (sildenafil, tadalafil, vardenafil) or NO donors (nitroglycerin).
• Relative
• Recent ischemic stroke or intracranial hemorrhage.
• Severe anemia (hematocrit <25 %).
• Acute myocardial infarction (use cautiously, under supervision).
• Warnings
• *Nitrate tolerance*: requires 10–12 h drug‑free interval daily.
• *Orthostatic hypotension*: especially in elderly, dehydrated, or dehydrating diuretic users.
• *Headache*: common, may indicate high dose or rapid titration.
• *Priapism*: rare but severe; avoid if patient uses PDE5 inhibitors.

Dosing

• Administration Tips
• Take with a meal if GI upset occurs.
• Do not crush sublingual tablets; chew orally or swallow whole.
• Use a 12–24 h nitrate‑free interval to prevent tolerance.

Adverse Effects

• Common
• Headache (≈30 %)
• Flushing, warmth
• Dizziness, light‑headedness
• Nausea, GI upset (rare)
• Serious
• Severe orthostatic hypotension → syncope or falls
• Priapism (especially with concurrent PDE5 inhibitors)
• Nitrate tolerance → breakthrough angina
• Rare: severe rash or hypersensitivity reactions

Monitoring

• Blood pressure: baseline and after each dose titration; check orthostatic BP.
• Heart rate & ECG: to monitor for arrhythmias or ischemic changes.
• Headache frequency/intensity: dose adjustment or adjunctive therapy if persistent.
• Renal & hepatic panels: annually; more frequently if clinically indicated.
• Patient diary: record angina episodes, dose changes, and side effects.

Clinical Pearls

• Titrate Slowly – 5 mg increments every 3–5 days to avoid headache surge and tolerance.
• Nitrate‑Free Window – a 12‑h drug‑free interval (often overnight) is essential; consider evening dose or split the dose to maintain steady plasma levels.
• Sublingual for Acute – use the Rapid form only for brief, episodic angina; it should *not* replace chronic maintenance dosing.
• Avoid Concomitant NO Donors – even topical nitroglycerin patches can precipitate severe hypotension if taken concurrently.
• Watch for Priapism – counsel patients using PDE5 inhibitors to seek immediate medical help if prolonged erection >4 h.
• Use with Antihypertensives – synergistic BP drop; monitor closely, especially in elderly or volume‑depleted patients.
• Switching from Isosorbide Dinitrate – IMN has a lower risk of tolerance and is preferred for long‑term therapy.

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• *Prepared for medical students and clinicians; references include product labeling and major cardiology guidelines (ACC/AHA 2022, ESC 2022).