Overview
Isosorbide mononitrate is an organic nitrate vasodilator used for the prophylaxis of angina pectoris. It is a long-acting metabolite of isosorbide dinitrate with more predictable pharmacokinetics due to complete bioavailability and minimal first-pass metabolism.
Mechanism of Action
Isosorbide mononitrate is converted to nitric oxide (NO) in vascular smooth muscle cells. NO activates guanylate cyclase, increasing cyclic GMP levels, leading to dephosphorylation of myosin light chains and subsequent vasodilation. This reduces preload and afterload, decreasing myocardial oxygen demand while improving coronary blood flow.
Indications
- Prophylaxis of angina pectoris
- Chronic stable angina
- Variant angina (Prinzmetal's angina)
Dosage
Initial dose: 20 mg twice daily (7 hours apart, with first dose on awakening). Maintenance: 20-40 mg twice daily. Extended-release tablets (Imdur): 30-60 mg once daily in morning, may increase to 120 mg once daily. Maximum dose: 240 mg daily.
Contraindications
- Hypersensitivity to nitrates
- Concurrent use with phosphodiesterase-5 inhibitors (sildenafil, tadalafil, vardenafil)
- Severe anemia
- Increased intracranial pressure
- Cardiac tamponade
- Constrictive pericarditis
Side Effects
- Headache (most common)
- Dizziness/lightheadedness
- Hypotension
- Flushing
- Nausea
- Syncope
- Reflex tachycardia
- Weakness
- Rash
Interactions
- Phosphodiesterase-5 inhibitors (sildenafil, tadalafil, vardenafil): severe hypotension
- Other vasodilators: additive hypotension
- Alcohol: enhanced hypotensive effects
- Calcium channel blockers: additive hypotension
- Heparin: reduced anticoagulant effect
- Aspirin: increased nitrate bioavailability