Imdur: Long-Acting Nitrate Therapy for Angina Prevention
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Synonyms | |||
Imdur (isosorbide mononitrate) is an extended-release nitrate medication specifically formulated for the prophylactic management of chronic stable angina pectoris. It belongs to the class of organic nitrates, which have been a cornerstone of anti-anginal therapy for decades. By reducing cardiac preload and afterload, Imdur decreases myocardial oxygen demand, thereby preventing the onset of anginal attacks. Its once-daily dosing regimen offers significant convenience and improves adherence compared to shorter-acting formulations, providing sustained protection and enhancing the quality of life for patients with coronary artery disease.
Features
- Active ingredient: Isosorbide mononitrate.
- Pharmacological class: Organic nitrate vasodilator.
- Formulation: Extended-release (ER) tablets.
- Available strengths: 30 mg, 60 mg, and 120 mg tablets.
- Mechanism of action: Venous and arterial vasodilation, reducing preload and afterload.
- Administration: Oral, once daily.
Benefits
- Provides 24-hour prophylactic coverage against anginal attacks with a single daily dose.
- Reduces the frequency of angina episodes and the need for sublingual nitroglycerin rescue.
- Decreases myocardial oxygen demand by reducing cardiac preload and afterload.
- Improves exercise tolerance and functional capacity in patients with chronic stable angina.
- Offers a predictable pharmacokinetic profile with a sustained release mechanism.
- Enhances patient adherence and quality of life through simplified dosing.
Common use
Imdur is indicated for the prevention of angina pectoris due to coronary artery disease. It is not intended for the acute relief of anginal attacks, for which sublingual nitroglycerin remains the standard of care. Its prophylactic use is most appropriate for patients experiencing frequent episodes of stable angina, aiming to reduce their occurrence and improve daily functioning. It is often used as part of a comprehensive management plan that may include beta-blockers, calcium channel blockers, and lifestyle modifications.
Dosage and direction
The dosage of Imdur must be individualized based on patient response and the presence of hemodynamic effects such as headaches or hypotension.
- Initial Dose: The usual starting dose is 30 mg or 60 mg administered orally once daily in the morning.
- Dose Titration: The dose may be increased to 120 mg once daily after several days if the clinical response is inadequate and the initial dose is well-tolerated. While some patients may benefit from 240 mg once daily, doses exceeding 240 mg have not been studied and are not recommended.
- Dosing Schedule: To minimize the development of tolerance (tachyphylaxis), a daily nitrate-low interval of 14-18 hours is recommended. This is naturally achieved with the once-daily dosing regimen. The tablet must be swallowed whole and must not be chewed, crushed, or split.
- Important Administration Note: Imdur may be taken with or without food. Patients should be advised to take the medication at the same time each day to maintain consistent plasma levels.
Precautions
- Tolerance Development: Continuous exposure to nitrates can lead to tolerance, diminishing the anti-anginal and anti-ischemic effects. The once-daily dosing schedule of Imdur is designed to provide a daily nitrate-free interval to prevent or minimize tolerance.
- Hypotension: Imdur can cause severe hypotension, especially in volume-depleted patients or those already taking other vasodilators or antihypertensive agents. This risk is heightened upon initiation or dose increases.
- Syncope: Even occasional episodes of symptomatic hypotension can lead to syncope, particularly when rising suddenly from a recumbent position.
- Angina exacerbation: Abrupt discontinuation of nitrate therapy can precipitate a rebound increase in the frequency and duration of anginal attacks, potentially leading to unstable angina or myocardial infarction. Dose reduction should be gradual.
- Aortic/Mitral Stenosis or Hypertrophic Cardiomyopathy: Nitrates should be used with extreme caution, if at all, in patients with these conditions, as reducing preload can cause a critical decrease in cardiac output.
- Headaches: A common dose-related side effect. Acetaminophen may be used for management. Headaches often diminish over time with continued therapy.
Contraindications
Imdur is contraindicated in patients with:
- Known hypersensitivity to isosorbide mononitrate, other nitrates, or any component of the formulation.
- Concurrent use of phosphodiesterase type 5 (PDE-5) inhibitors (e.g., sildenafil, tadalafil, vardenafil) or soluble guanylate cyclase (sGC) stimulators (e.g., riociguat). Concomitant use can cause profound hypotension, syncope, or myocardial infarction.
- Marked anemia, increased intracranial pressure (e.g., following head trauma or cerebral hemorrhage), or severe hypotension (systolic BP < 90 mmHg).
- Circulatory failure and shock states.
Possible side effect
The most common side effect is headache, which is often throbbing and dose-related. Other possible adverse reactions include:
- Very Common (>10%): Headache.
- Common (1-10%): Dizziness, nausea, vomiting, flushing, hypotension (manifested as lightheadedness, vertigo, or syncope upon standing), increased heart rate (reflex tachycardia).
- Uncommon (0.1-1%): Dermatitis, rash, pruritus, weakness, palpitations, orthostatic hypotension.
- Rare (<0.1%): Exfoliative dermatitis, gastrointestinal upset, methemoglobinemia (especially in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency or other predisposing factors).
Drug interaction
Imdur has significant pharmacokinetic and pharmacodynamic interactions:
- Phosphodiesterase-5 Inhibitors (e.g., Sildenafil, Tadalafil, Vardenafil): Absolute Contraindication. Concomitant use potentiates severe, life-threatening hypotension.
- Soluble Guanylate Cyclase Stimulators (e.g., Riociguat): Absolute Contraindication. Profound hypotension can occur.
- Other Vasodilators (e.g., Calcium Channel Blockers, ACE Inhibitors, ARBs, Alpha-blockers, other nitrates): Increased risk of hypotension. Blood pressure must be monitored closely.
- Alcohol: Potentiates the vasodilatory and hypotensive effects of Imdur.
- Dihydroergotamine: Concomitant use may decrease the vasoconstrictive effect of dihydroergotamine.
- Antihypertensive Agents: Additive hypotensive effect.
Missed dose
- If a dose of Imdur is missed, the patient should take it as soon as they remember on the same day.
- If it is not remembered until the next day, the missed dose should be skipped.
- The patient should never take a double dose to make up for a missed one, as this significantly increases the risk of severe hypotension and other adverse effects.
- The regular once-daily schedule should be resumed the following day.
Overdose
Nitrate overdose is primarily characterized by vasodilation leading to severe hypotension with persistent throbbing headache, vertigo, palpitations, visual disturbances, flushing, sweating, nausea, vomiting, and syncope. Methemoglobinemia is a rare but serious complication, presenting with cyanosis, anemia, hypoxia, fatigue, and dyspnea.
- Management: There is no specific antidote. Primary treatment involves placing the patient in a supine position in a shock position (legs elevated) to support venous return and blood pressure. Administer IV fluids for volume expansion. If methemoglobinemia is suspected and confirmed, methylene blue (1-2 mg/kg IV over 5 minutes) is the treatment of choice. Supportive care for hypoxia and hypotension is critical. Hemodialysis is not effective for removing isosorbide mononitrate.
Storage
- Store Imdur tablets at room temperature, between 20°C to 25°C (68°F to 77°F).
- Protect from moisture and light. Keep the bottle tightly closed.
- Keep all medications out of the reach of children and pets.
- Do not use beyond the expiration date printed on the packaging.
Disclaimer
This information is for educational and informational purposes only and does not constitute medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting, stopping, or changing any prescribed therapy. Never disregard professional medical advice or delay in seeking it because of something you have read here. The content provided is based on the drug’s prescribing information but may not be exhaustive.
Reviews
- Clinical Efficacy (Cardiology Journal): “In a randomized, double-blind study, once-daily Imdur 120 mg demonstrated a statistically significant increase in total exercise duration and time to onset of angina compared to placebo, confirming its efficacy as a prophylactic anti-anginal agent with a favorable once-daily dosing profile.”
- Tolerability Assessment (Pharmacotherapy Review): “While headache is a nearly universal initial side effect, it typically subsides with continued use in a majority of patients. The extended-release formulation provides a steady-state plasma concentration, minimizing peak-dose side effects and contributing to its overall tolerability.”
- Patient Adherence Study (Patient Preference and Adherence): “The simplified once-daily regimen of Imdur was associated with a significantly higher adherence rate (>85%) compared to shorter-acting nitrate formulations requiring multiple daily doses, directly contributing to more consistent therapeutic outcomes.”