Isordil (Isosorbide dinitrate)

Isordil (Isosorbide Dinitrate): Patient Information for Australia

Basic Product Information

Mechanism of Action

Patient-friendly explanation: Isosorbide dinitrate is a type of nitrate medicine. It works by relaxing and widening blood vessels. This lowers the heart's workload and increases blood flow to the heart muscle, helping to prevent or relieve chest pain (angina).

For healthcare specialists: Isosorbide dinitrate is a nitric oxide donor, converted in vascular smooth muscle to nitric oxide, which activates guanylate cyclase. The resulting increase in cGMP induces smooth muscle relaxation, causing vasodilation of veins (mainly) and arteries, reducing preload, afterload, and myocardial oxygen demand.

Pharmacokinetics

• Absorption: Rapidly absorbed after oral and sublingual administration; bioavailability 25–50% (significant first-pass metabolism).
• Onset: Sublingual: 2–5 min (for acute angina); Oral: 15–60 min.
• Peak effect: 1–2 hours (oral tablets).
• Metabolism: Extensive hepatic metabolism to active metabolites (isosorbide-2-mononitrate and isosorbide-5-mononitrate).
• Elimination: Renal (~80%) and faecal routes.
• Duration: 4–6 hours (oral), 1–2 hours (sublingual).
• Half-life: 1–5 hours depending on formulation.

Use in Everyday Life and Best Practices

Isordil is mainly used to prevent and relieve angina attacks. It is not suitable for immediate relief—sublingual tablets are preferred for rapid action. Follow your doctor’s instructions about the timing and dosage.

• How to take: Swallow oral tablets with water; allow sublingual tablets to dissolve under the tongue without chewing or swallowing for fastest effect.
• Timing: Take at the same time each day for best results. The regimen may involve once, twice, or three times a day dosing. An interval-free (nitrate-free) period each day is usually recommended to prevent tolerance—often overnight or for 12 hours (e.g., 8 am and 2 pm doses).
• Do not stop suddenly: Stopping abruptly can worsen angina. Discuss with your GP before making changes. Always carry your sublingual tablets for emergencies.
• Driving and machinery: As Isordil can cause dizziness or light-headedness, take care after your first few doses or if your dose is changed.

Dosing: Morning vs Evening

• Morning dosing: Often preferred to fit "nitrate-free" overnight intervals (reducing tolerance risk). This may coincide with daily routines for better adherence.
• Evening dosing: Usually only recommended for patients with increased angina symptoms overnight or if prescribed by a specialist.
• Tip: Take doses at the same times each day. Allow a 10–12 hour gap between doses (e.g., 8 am and 2 pm) for maximum effectiveness and minimal tolerance.

Taking with Food or on an Empty Stomach

Isordil tablets can be taken with or without food. Some patients prefer to take it after meals to minimise stomach upset. A typical English diet does not interfere with absorption, but rich, fatty meals may slightly delay its effect. Avoid grapefruit and grapefruit juice as they can alter how the medicine is processed.

• With food: May reduce stomach discomfort.
• Empty stomach: May speed up absorption, especially for sublingual forms.
• Alcohol: Increases risk of low blood pressure, dizziness—best to limit or avoid.

Interaction Warnings

Indications

Dosing According to Clinical Indications

Safety Profile & Side Effects

• Common: Headache, dizziness, light-headedness especially when standing up, flushing, nausea
• Less common: Low blood pressure (hypotension), faster heart beat (tachycardia), palpitations, fainting
• Rare/Serious: Severe hypotension, allergic reactions (rash, swelling), worsening of angina on starting or increasing dose (rare, “paradoxical” effect)
• Warning: Sudden discontinuation can increase risk of angina attacks or heart problems

Guidelines for Proper Use

• Take Isordil exactly as prescribed by your doctor. Do not adjust the dose yourself.
• Plan doses to allow a “nitrate-free” interval every day (usually overnight) to maintain effect and reduce tolerance.
• If you miss a dose and it is almost time for your next dose, skip the missed one. Do not double up.
• Store tablets in their original packaging away from light, heat, and moisture. Check expiry dates regularly.
• Have regular check-ups with your GP or specialist. Bring your medicine list and any concerns.
• For planned surgery or dental procedures, inform your doctor you are taking Isordil.
• If you experience severe dizziness, a sudden increase in chest pain, or allergic symptoms, seek urgent medical help.
• For travel, keep medicines with you in hand luggage; have a supply of sublingual tablets for emergencies.

Alternative Treatment Options (PBS-Reimbursed)

• Glyceryl trinitrate (Nitrolingual, Anginine): Rapid acting for acute angina. Pros: Fast; Cons: Short duration.
• Isosorbide mononitrate (Imdur): Longer acting, often once daily. Pros: Convenient dosing; Cons: Not suitable for acute relief.
• Beta-blockers (e.g., atenolol, metoprolol): For angina or high blood pressure; often used with nitrates. Pros: Cardiac protection; Cons: Not all patients tolerate.
• Calcium channel blockers (e.g., amlodipine, verapamil): For angina and hypertension. Pros: Useful if nitrates cause side effects; Cons: Can cause fluid retention or leg swelling.

All listed alternatives are available on the Australian PBS (Pharmaceutical Benefits Scheme). Choice depends on individual condition, tolerance, and co-existing conditions, and should always be discussed with your prescriber.

Legal, Registration, and Reimbursement Status in Australia

• Therapeutic Goods Administration (TGA): Isosorbide dinitrate is TGA-approved and regulated for angina pectoris treatment.
• Schedule: S4 – Prescription Only Medicine.
• PBS (Pharmaceutical Benefits Scheme): Isordil and alternatives (Isosorbide mononitrate, GTN) are reimbursed for eligible patients.
• Authority required: For specific heart failure indications, specialist approval may be needed.
• Patient support: My Health Record provides national e-script & dispensing tracking.

Latest Research & Clinical Guidance (2022–2025)

• Heart Foundation Australia (2023 update): Nitrates remain a core component of stable angina management; intermittent (“nitrate-free”) regimens reduce tolerance risk; importance of combined therapy with beta-blockers and antiplatelet agents when appropriate.
• ESC/EACTS Guidelines (2023): For chronic coronary syndromes, long-acting nitrates provide symptom relief; use should be individualised; limited evidence for primary prevention of heart attacks in stable disease.
• Australian Institute of Health and Welfare (2024): Substantial reductions in hospital admissions for angina with proactive secondary prevention, including nitrate use and lifestyle modification.
• Recent clinical trials: Newer nitrates (e.g., isosorbide mononitrate) show similar efficacy to Isordil with once-daily dosing, though Isordil remains useful where flexible titration is needed.

Availability and Delivery

Isordil is widely available in Australian community and hospital pharmacies, often dispensed in the following pack sizes:

FAQ – Common Questions About Isordil

1. Can I drive while taking Isordil? Some people may feel dizzy or lightheaded, especially after starting or changing their dose. Only drive if you feel well and are sure the medicine does not affect your alertness.
2. What should I do if I miss a dose? Take your next dose at the scheduled time. Do not double up or take two doses together. Stick to a regular dosing routine if possible.
3. Can I take Isordil with my other heart medicines? Yes, but it is important to inform your doctor and pharmacist about all your medicines as some combinations need special care—especially with blood pressure medications and other nitrates.
4. What if I am pregnant or breastfeeding? Isordil is only used in pregnancy or breastfeeding if your doctor recommends it. Discuss your individual circumstances with your healthcare provider.
5. Is there a difference between Isordil and Imdur? Isordil (isosorbide dinitrate) and Imdur (isosorbide mononitrate) are related but have slightly different uses and dosing schedules. Imdur is often once daily, Isordil is usually multiple times daily. Your doctor will recommend the one most suitable for you.