Imdur (Isosorbide 5 Mononitrate)

Imdur (isosorbide 5 mononitrate) is employed in the management of coronary artery disease‑related angina syndromes.

• Prophylaxis of angina pectoris: reduces the frequency of angina attacks and improves exercise tolerance in patients with chronic stable angina.
• Chronic stable angina: provides long‑term symptom control, decreasing myocardial oxygen demand during physical activity.
• Angina pectoris (stable): helps prevent episodes of chest pain associated with exertion or emotional stress.
• Prevention of angina during stress testing: facilitates safe completion of diagnostic exercise tests by minimizing chest pain.

• Isosorbide 5 mononitrate is absorbed from the gastrointestinal tract and undergoes biotransformation to release nitric oxide. The nitric oxide activates guanylate cyclase, increasing cyclic GMP levels in vascular smooth muscle. Elevated cGMP causes relaxation of arterial and venous vessels, producing vasodilation, reducing preload and afterload, and consequently lowering myocardial oxygen consumption during cardiac work. The effect persists throughout the dosing interval, providing steady anti‑anginal protection.

Isosorbide 5 mononitrate may cause a range of adverse reactions, which are generally categorized by frequency and severity.

Common Side Effects

• Headache: throbbing pain often occurring shortly after dosing.
• Flushing: warm sensation and redness of the skin.
• Dizziness or light‑headedness: especially when standing quickly.
• Nausea: mild stomach upset.
• Low blood pressure: mild orthostatic hypotension.
• Palpitations: awareness of rapid or irregular heartbeat.

Serious or Rare Side Effects

• Severe hypotension: marked drop in blood pressure leading to fainting.
• Syncope: sudden loss of consciousness.
• Allergic reaction: rash, itching, swelling, or difficulty breathing.
• Methemoglobinemia: bluish discoloration of skin and mucous membranes.
• Cardiac arrhythmia: irregular heart rhythm requiring medical attention.
• Chest pain worsening: may indicate myocardial ischemia.

Before prescribing Imdur, clinicians should consider several precautionary measures to ensure safe use.

• Assess cardiovascular status: evaluate blood pressure and heart rate prior to initiation.
• Avoid concurrent PDE‑5 inhibitors: co‑administration can cause profound hypotension.
• Monitor for tolerance development: efficacy may diminish with prolonged use.
• Adjust dosing in renal impairment: consider reduced dose or increased monitoring.
• Counsel on abrupt discontinuation: sudden stop may precipitate angina recurrence.
• Store at ambient temperature below 25°C: keep in the original pack, protect from moisture.

Isosorbide 5 mononitrate interacts with several drug classes; awareness of these interactions helps prevent adverse events.

Major Interactions (Avoid)

• Other nitrates (e.g., nitroglycerin): combined use can cause severe hypotension.
• Phosphodiesterase‑5 inhibitors (e.g., sildenafil): may lead to dangerous blood pressure drops.
• Antihypertensive agents (e.g., ACE inhibitors, beta‑blockers): additive blood pressure‑lowering effect.

Moderate Interactions (Monitor Closely)

• Diuretics: may enhance orthostatic hypotension, requiring blood pressure monitoring.
• Alcohol: can increase vasodilatory effects and dizziness.
• CYP3A4 inhibitors (e.g., erythromycin): may raise plasma levels of isosorbide 5 mononitrate.