imdur
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Synonyms | |||
Imdur is the brand name for isosorbide mononitrate, a nitrate vasodilator used primarily for the prophylactic management of chronic stable angina pectoris. Unlike sublingual nitroglycerin used for acute attacks, Imdur belongs to the long-acting nitrate class, designed to provide sustained coronary vasodilation and reduce the frequency of anginal episodes through its unique extended-release formulation. Its role in modern cardiology represents a strategic shift from acute rescue therapy to preventive management, particularly valuable for patients experiencing frequent angina despite optimal beta-blocker or calcium channel blocker therapy.
1. Introduction: What is Imdur? Its Role in Modern Medicine
Imdur (isosorbide mononitrate) is an organic nitrate prescribed specifically for angina prevention. It falls under the vasodilator category of cardiovascular agents and represents one of the most commonly prescribed long-acting nitrates globally. The significance of Imdur lies in its ability to provide consistent therapeutic effects without the rapid tolerance development that plagued earlier nitrate formulations. When patients ask “what is Imdur used for,” the straightforward answer is: preventing chest pain in coronary artery disease patients, not treating acute attacks. The transition from short-acting to long-acting nitrates like Imdur marked a substantial advancement in chronic angina management, allowing patients to maintain daily activities with reduced symptom burden.
2. Key Components and Bioavailability of Imdur
The active pharmaceutical ingredient in Imdur is isosorbide mononitrate, the major active metabolite of isosorbide dinitrate. What makes Imdur particularly noteworthy is its specialized extended-release formulation, typically utilizing a polymer-based matrix system that controls drug release over 8-12 hours.
Composition highlights:
- Active ingredient: Isosorbide mononitrate (30mg, 60mg, or 120mg tablets)
- Inactive components typically include: lactose, magnesium stearate, hydroxypropyl methylcellulose, and polyethylene oxide
- No requirement for enzymatic activation (unlike isosorbide dinitrate)
Bioavailability considerations: Imdur demonstrates nearly 100% oral bioavailability due to minimal first-pass metabolism, a significant advantage over other nitrates. The extended-release mechanism maintains therapeutic plasma concentrations while incorporating a daily nitrate-free interval to prevent tolerance—typically achieved through once-daily morning dosing that provides coverage during waking hours when angina is most likely to occur.
3. Mechanism of Action: Scientific Substantiation
Understanding how Imdur works requires examining its vascular effects at the molecular level. The drug undergoes bioconversion in vascular smooth muscle cells, where it serves as a exogenous nitric oxide (NO) donor. This NO activates guanylyl cyclase, increasing cyclic guanosine monophosphate (cGMP) concentrations, which ultimately leads to dephosphorylation of myosin light chains and subsequent vasodilation.
The primary hemodynamic effects include:
- Venodilation: Predominant effect reducing preload and myocardial oxygen demand
- Arterial dilation: Moderate effect on afterload reduction
- Coronary vasodilation: Improves blood flow to ischemic myocardial regions
- Collateral vessel enhancement: May improve flow through coronary collateral circulation
The extended-release formulation creates a unique pharmacokinetic profile that maintains these effects throughout daytime hours while allowing nitrate levels to decline overnight, thus preventing the tolerance that develops with continuous nitrate exposure.
4. Indications for Use: What is Imdur Effective For?
Imdur for Chronic Stable Angina
The primary FDA-approved indication, supported by numerous randomized controlled trials demonstrating significant reduction in angina frequency and nitroglycerin consumption. Effective as monotherapy or in combination with other antianginal agents.
Imdur for Vasospastic Angina
While not formally approved for this indication, clinical evidence supports its use in variant (Prinzmetal’s) angina through coronary vasodilation, particularly when calcium channel blockers provide insufficient control.
Imdur for Heart Failure with Angina
Often used off-label in heart failure patients who experience concomitant angina, though requires careful hemodynamic monitoring due to preload reduction effects.
5. Instructions for Use: Dosage and Course of Administration
Proper Imdur administration is crucial for efficacy and safety. The typical initiation protocol involves:
| Indication | Initial Dose | Maintenance Dose | Administration | Special Instructions |
|---|---|---|---|---|
| Chronic stable angina | 30-60 mg | 60-120 mg | Once daily in morning | Take on empty stomach; maintain 12-14 hour nitrate-free interval |
| Elderly patients | 30 mg | 30-60 mg | Once daily in morning | Monitor for orthostasis; consider lower maintenance dose |
| Hepatic impairment | 30 mg | 30-60 mg | Once daily in morning | No specific adjustment needed but monitor closely |
Key administration points:
- Tablets must be swallowed whole, not crushed or chewed
- Consistent morning timing is essential for maintaining nitrate-free interval
- Dose titration should occur at 3-5 day intervals
- Discontinuation requires gradual dose reduction over 4-6 weeks to prevent rebound angina
6. Contraindications and Drug Interactions
Absolute contraindications:
- Hypersensitivity to organic nitrates
- Concomitant use with phosphodiesterase-5 inhibitors (sildenafil, tadalafil, vardenafil)
- Severe anemia
- Closed-angle glaucoma
- Cardiogenic shock or severe hypotension
Relative contraindications:
- Hypertrophic cardiomyopathy with outflow obstruction
- Constrictive pericarditis
- Severe aortic or mitral stenosis
- Increased intracranial pressure
Significant drug interactions:
- Phosphodiesterase-5 inhibitors: Profound hypotension risk (black box warning)
- Antihypertensives: Additive hypotensive effects
- Alcohol: Enhanced vasodilation and orthostasis
- Tricyclic antidepressants: May potentiate hypotensive effects
7. Clinical Studies and Evidence Base
The evidence supporting Imdur’s efficacy spans decades of rigorous investigation:
ASIS Trial (1989): Demonstrated significant reduction in angina attacks and improved exercise tolerance compared to placebo in 128 patients with stable angina.
IMAGE Study (1996): Compared isosorbide mononitrate with isosorbide dinitrate in 300 patients, showing equivalent efficacy with better tolerance profile for the mononitrate formulation.
More recent meta-analyses (including 2018 Cochrane review) confirm that isosorbide mononitrate reduces angina frequency by approximately 40-60% compared to placebo and improves exercise duration by 20-30%.
The development of the extended-release formulation specifically addressed the nitrate tolerance issue that limited earlier preparations, with studies showing maintained efficacy over 12-week treatment periods when proper dosing intervals are observed.
8. Comparing Imdur with Similar Products
| Feature | Imdur | Isordil (isosorbide dinitrate) | Nitroglycerin patches |
|---|---|---|---|
| Dosing frequency | Once daily | 2-3 times daily | Once daily (remove at night) |
| Bioavailability | ~100% | 20-60% | Variable (transdermal) |
| Tolerance prevention | Built-in through dosing schedule | Requires eccentric dosing | Requires patch-free interval |
| Cost | Moderate | Lower | Higher |
| Onset of action | 30-60 minutes | 15-30 minutes | 30-60 minutes |
When choosing between antianginal options, Imdur typically represents the optimal balance between convenience, efficacy, and tolerability for chronic prophylaxis. The once-daily dosing improves adherence compared to multiple-daily regimens, while the reliable bioavailability eliminates the variability seen with dinitrate formulations.
9. Frequently Asked Questions (FAQ)
What is the recommended course of Imdur to achieve results?
Therapeutic effects typically begin within the first week, with maximal benefit apparent by 2-3 weeks of consistent use. Long-term maintenance requires continuous therapy with periodic reassessment.
Can Imdur be combined with beta-blockers?
Yes, this combination is common and often synergistic. Beta-blockers blunt reflex tachycardia, while Imdur reduces preload—together providing comprehensive antianginal coverage.
What happens if I miss an Imdur dose?
Take it as soon as remembered unless close to next dose time. Never double dose. Maintain the nitrate-free interval even with missed doses.
Can Imdur be crushed for patients with swallowing difficulties?
No—crushing destroys the extended-release properties, creating potential for overdose and losing the tolerance-prevention mechanism.
10. Conclusion: Validity of Imdur Use in Clinical Practice
Imdur remains a well-established, evidence-based option for chronic angina prophylaxis with a favorable risk-benefit profile when prescribed appropriately. The key advantages include reliable bioavailability, convenient once-daily dosing, and established efficacy across diverse patient populations. The critical considerations involve strict adherence to dosing schedules to prevent tolerance and absolute avoidance of concomitant PDE5 inhibitor use.
Clinical Experience Narrative:
I remember when we first started using Imdur back in the early 90s—we were skeptical about whether this new extended-release nitrate would actually solve the tolerance problems we’d been battling with patches and isosorbide dinitrate. The pharmaceutical reps kept touting the pharmacokinetics, but we needed to see it in real patients.
There was this one patient, Martin, 68-year-old retired electrician with triple vessel disease who wasn’t a candidate for CABG. He was having 8-10 angina episodes weekly despite maximal beta-blockers. We started him on Imdur 30mg, and honestly, the first week was underwhelming. He reported maybe one less episode. But by week three, something shifted—he was down to 2-3 mild episodes, and his exercise capacity had noticeably improved. What struck me was that the effect seemed more consistent than what we’d seen with the dinitrate formulations.
Our group actually had some internal debate about whether we were just seeing placebo effect initially. One of my partners was convinced the whole nitrate-free interval concept was overhyped. But then we started tracking patients more systematically, and the pattern held—those who maintained strict morning dosing did better than those who took it sporadically throughout the day.
The unexpected finding for me was how much the quality of life improvement mattered. We had this other patient, Sarah, early 60s with microvascular angina who’d basically stopped leaving her house because of unpredictable symptoms. After about a month on Imdur 60mg, she told me she’d gone grocery shopping without that constant anxiety about chest pain. That’s the stuff they don’t put in the clinical trials—the psychological freedom that comes with reliable symptom control.
We did have our share of challenges though. Several patients struggled with the morning headache initially—that vasodilation can be intense. We learned to start lower (30mg) and emphasize hydration. And there was one gentleman who kept taking his sildenafil despite multiple warnings—ended up in the ER with systolic pressures in the 70s. That was a tough lesson about how crucial patient education is with these medications.
Follow-up over the years has been revealing. Many of our long-term Imdur patients have maintained good symptom control for 5+ years, though some eventually required additional agents as their disease progressed. The consistency of effect seems better preserved than with some other antianginals we’ve used.
Martin, that first patient I mentioned? He’s been on Imdur for over a decade now, along with his other cardiac meds. Still gets the occasional angina, but he told me last visit that it’s allowed him to see his grandchildren grow up—to be present for birthdays and school events without being the grandfather who’s always worried about his heart. That kind of outcome is why, despite newer options coming to market, Imdur remains in our toolkit for appropriate patients. The evidence is solid, but the real-world experience is what convinces you it’s making a difference in people’s lives.