Monoket Retard (Isosorbide Mononitrate)

Isosorbide Mononitrate is employed in the management of coronary artery disease, particularly angina pectoris.

• Prophylaxis of angina pectoris: reduces the frequency of angina attacks in patients with stable angina.
• Treatment of chronic stable angina: improves exercise tolerance and lessens chest‑pain episodes.
• Long‑acting nitrate therapy for patients unable to use short‑acting nitrates: provides sustained vasodilation and symptom control.

• Isosorbide Mononitrate is metabolized to release nitric oxide, which activates guanylate cyclase in vascular smooth muscle. The resulting increase in cyclic GMP causes relaxation of arterial and venous vessels, lowering preload and afterload, and thereby enhancing myocardial oxygen supply while reducing cardiac workload.

Isosorbide Mononitrate may cause a range of adverse reactions.

Common Side Effects

• Headache: throbbing pain often occurring shortly after dosing.
• Dizziness or light‑headedness: related to blood pressure lowering.
• Flushing: warm sensation and reddening of the skin.
• Nausea: mild gastrointestinal upset.
• Palpitations: awareness of heartbeat.
• Hypotension: mild drop in blood pressure.

Serious or Rare Side Effects

• Severe hypotension: marked blood pressure fall requiring medical attention.
• Syncope: sudden loss of consciousness.
• Myocardial infarction: rare but reported in susceptible patients.
• Allergic reactions: rash, itching, or swelling.
• Stevens‑Johnson syndrome: severe skin reaction.
• Methemoglobinemia: abnormal hemoglobin causing cyanosis.

When prescribing or dispensing Isosorbide Mononitrate, several safety considerations apply.

• Dose titration: start with a low dose and increase gradually to minimise hypotension.
• Concomitant PDE‑5 inhibitors: avoid use together because of risk of profound hypotension.
• Blood pressure monitoring: check for symptomatic hypotension, especially after dose changes.
• Renal impairment: consider dose adjustment in patients with reduced renal function.
• Pregnancy and lactation: use only if the potential benefit justifies the potential risk to the fetus or infant.
• Store at room temperature: keep in the original container, protect from moisture and light.

Isosorbide Mononitrate can interact with several drug classes.

Major Interactions (Avoid)

• Phosphodiesterase‑5 inhibitors (e.g., sildenafil, tadalafil): may cause severe hypotension.
• Other nitrates (e.g., nitroglycerin, isosorbide dinitrate): additive vasodilatory effect leading to dangerous blood pressure drops.
• Antihypertensive agents (e.g., ACE inhibitors, beta‑blockers): may enhance blood‑pressure‑lowering actions.

Moderate Interactions (Monitor Closely)

• Alcohol: can increase the risk of hypotension and dizziness.
• Diuretics: may cause volume depletion and amplify blood‑pressure reduction.
• Azole antifungals (e.g., ketoconazole): may raise nitrate plasma concentrations.