Drug Class: Organic Nitrate | Vasodilator | Form: Oral Sustained-Release Tablet | Prescription Status: Prescription Only (Rx) — DRAP Registered
What is Sustac 6.4mg Tablet?
Sustac 6.4mg contains Glyceryl Trinitrate (GTN) — also known as Nitroglycerin — one of the longest-established and most clinically proven medicines in cardiovascular care. Unlike fast-acting GTN sprays or sublingual tablets used for immediate angina relief, Sustac 6.4mg is a sustained-release oral tablet designed for the long-term prevention and management of angina pectoris (سینے کا درد). It releases Glyceryl Trinitrate gradually over an extended period — maintaining a steady therapeutic level in the blood that keeps blood vessels relaxed and widened throughout the day. This sustained vasodilation reduces the heart's workload, improves oxygen delivery to the heart muscle, and prevents the episodes of chest pain that occur when the heart's oxygen demand exceeds its supply. Sustac 6.4mg is used for chronic angina management, certain heart failure conditions, and specific coronary artery disorders under medical supervision.
What is Sustac 6.4mg Used For?
- Chronic stable angina pectoris — long-term prevention of chest pain episodes caused by reduced blood flow to the heart muscle (سینے کے درد کی روک تھام)
- Unstable angina — adjunctive management of unstable angina under close medical supervision (غیر مستقل سینے کا درد)
- Vasospastic angina (Prinzmetal's angina) — prevention of chest pain caused by coronary artery spasm
- Congestive heart failure — reducing cardiac preload and afterload to improve heart pumping efficiency in selected heart failure patients (دل کی ناکامی)
- Coronary artery disease — long-term management of symptoms in patients with established coronary artery narrowing
- Post-myocardial infarction — selected use in patients following heart attack to reduce cardiac workload under specialist supervision
How Does Sustac 6.4mg Work?
Venous and Arterial Vasodilation: Glyceryl Trinitrate is converted inside blood vessel cells into nitric oxide — a powerful natural vasodilator. Nitric oxide activates an enzyme called guanylate cyclase, which increases cyclic GMP levels inside smooth muscle cells — causing them to relax. This relaxation produces vasodilation in both veins and arteries throughout the body.
Reduction of Cardiac Preload: Venous dilation reduces the amount of blood returning to the heart — lowering the filling pressure (preload) that the heart muscle must work against with each beat. This directly reduces myocardial oxygen demand and relieves the strain on an overworked or oxygen-deprived heart muscle.
Reduction of Cardiac Afterload: Arterial dilation reduces the resistance against which the heart pumps blood into the circulation — lowering afterload and further reducing the heart's oxygen requirement. This combination of preload and afterload reduction makes GTN particularly effective in both angina and heart failure.
Coronary Artery Dilation: GTN also dilates the coronary arteries themselves — improving blood flow and oxygen delivery directly to the heart muscle, particularly valuable in vasospastic angina where coronary spasm restricts blood flow.
Sustained-Release Mechanism: Unlike immediate-acting GTN formulations, Sustac 6.4mg releases Glyceryl Trinitrate gradually and continuously — maintaining therapeutic nitrate levels in the blood for sustained angina prevention rather than acute symptom relief.
Dosage and Administration
⚠️ Always take exactly as prescribed by your doctor. Never stop Sustac suddenly without medical advice. Sustac is NOT a rescue medicine — always keep a fast-acting GTN spray or sublingual tablet for acute angina attacks.
| Indication | Usual Adult Dose | Frequency | Maximum Daily Dose |
|---|---|---|---|
| Chronic stable angina | 1 tablet (6.4mg) | Two to three times daily | As prescribed |
| Heart failure (adjunctive) | 1 tablet (6.4mg) | Two to three times daily | As prescribed |
| Vasospastic angina | 1 tablet (6.4mg) | Two to three times daily | As prescribed |
Critical Dosing Rules:
- Nitrate tolerance — taking GTN continuously around the clock causes the body to become less responsive to its effects; your doctor will prescribe a nitrate-free interval of 8 to 12 hours daily — usually overnight — to prevent tolerance from developing
- Never crush or chew Sustac tablets — this is a sustained-release formulation; crushing destroys the controlled-release mechanism and releases the full dose at once causing dangerous sudden drop in blood pressure
- Never use Sustac as a rescue medicine for acute angina attacks — use a fast-acting GTN spray or sublingual tablet for sudden chest pain
- Never stop suddenly — abrupt discontinuation can trigger rebound angina or even heart attack in patients with coronary artery disease
- Blood pressure must be monitored regularly — GTN significantly lowers blood pressure and the risk of hypotension is highest in the first hours after each dose
- Dose adjustment required in elderly patients — more sensitive to blood pressure lowering effects and headache
How to Take:
- Swallow the tablet whole with a full glass of water — never crush, split, or chew
- May be taken with or without food — take consistently the same way each day
- Take at evenly spaced times as prescribed — maintaining the nitrate-free interval advised by your doctor
- Sit or lie down after taking — GTN can cause sudden dizziness particularly with the first few doses
- If a dose is missed, take it as soon as remembered — skip if it is nearly time for the next dose; never double the dose
Active Ingredients
| Ingredient | Strength per Tablet |
|---|---|
| Glyceryl Trinitrate (Nitroglycerin) | 6.4mg |
Who Should NOT Take Sustac 6.4mg?
Do not take if you:
- Are allergic to Glyceryl Trinitrate, any organic nitrate, or any ingredient in the tablet
- Have taken a PDE-5 inhibitor — Sildenafil (Viagra), Tadalafil, or Vardenafil — within the last 24 to 48 hours — this combination causes a life-threatening and potentially fatal drop in blood pressure
- Have severe hypotension — systolic blood pressure below 90mmHg
- Have hypertrophic obstructive cardiomyopathy
- Have severe aortic stenosis or mitral stenosis
- Have constrictive pericarditis or cardiac tamponade
- Have raised intracranial pressure or recent head injury
- Have severe anaemia
- Are taking soluble guanylate cyclase stimulators (e.g., Riociguat) — contraindicated combination
Always consult your doctor before taking Sustac if you have:
- Low blood pressure or are prone to dizziness on standing (ہائی بلڈ پریشر کی ادویات لے رہے ہیں)
- Recent heart attack — use only under strict specialist supervision
- Hypothyroidism or malnutrition
- Liver or kidney disease
- Glaucoma (آنکھوں کا دباؤ) — GTN can raise intraocular pressure
- Are elderly — significantly more sensitive to blood pressure lowering effects
- Are pregnant or breastfeeding
- Are taking antihypertensives, calcium channel blockers, or other vasodilators — additive hypotension risk
Side Effects
Common Side Effects:
- Headache — most common and expected side effect of GTN; caused by cerebral vasodilation; usually improves with continued use and manageable with simple analgesics
- Dizziness or light-headedness — particularly when standing up quickly; sit or lie down after taking
- Flushing — feeling of warmth or redness in the face and neck — vasodilation related
- Palpitations — awareness of heartbeat; reflex tachycardia from blood pressure lowering
- Nausea — mild and usually temporary
- Nitrate tolerance — reduced effectiveness with continuous around-the-clock use; managed by prescribing a daily nitrate-free interval
Serious Side Effects — Stop Taking and Seek Medical Help Immediately:
- Severe hypotension — extreme dizziness, fainting, or collapse — particularly dangerous if PDE-5 inhibitors have been taken recently; this is a life-threatening emergency (طبی ہنگامی صورتحال)
- Paradoxical bradycardia — unusually slow heart rate with worsening chest pain in some patients — stop and seek immediate cardiac evaluation
- Methaemoglobinaemia — rare but serious condition causing reduced oxygen-carrying capacity of the blood at very high doses — bluish discolouration of lips and fingertips, severe breathlessness; seek emergency care immediately
- Severe allergic reaction — swelling of face, lips, tongue or throat, difficulty breathing, widespread rash (یہ طبی ہنگامی صورتحال ہے)
- Worsening angina — rebound chest pain if Sustac is stopped suddenly without tapering; never discontinue abruptly
- Syncope — sudden loss of consciousness from severe blood pressure drop — particularly with first doses or in combination with other vasodilators
Drug Interactions
| Medicine / Substance | Possible Interaction |
|---|---|
| PDE-5 Inhibitors — Sildenafil (Viagra), Tadalafil, Vardenafil | Absolutely contraindicated — combination causes catastrophic and potentially fatal drop in blood pressure; never take within 24–48 hours of any nitrate |
| Riociguat (soluble guanylate cyclase stimulator) | Contraindicated — additive and potentially fatal hypotension risk |
| Antihypertensives (e.g., Amlodipine, Losartan, Beta-blockers) | Additive blood pressure lowering — significant hypotension risk; monitor blood pressure carefully |
| Calcium channel blockers (e.g., Diltiazem, Verapamil) | Additive vasodilation and blood pressure lowering — increased hypotension and dizziness risk |
| Other nitrates or vasodilators | Additive vasodilation — dangerous hypotension risk; avoid combining |
| Tricyclic antidepressants (e.g., Amitriptyline) | Enhance hypotensive effect of GTN — increased dizziness and fainting risk |
| Antipsychotics (e.g., Haloperidol, Chlorpromazine) | Additive blood pressure lowering — excessive hypotension risk |
| Heparin | GTN infusion may reduce Heparin effectiveness — monitor anticoagulation levels closely |
| Ergotamine | GTN increases bioavailability of Ergotamine — risk of ergotamine-induced vasoconstriction and angina worsening |
| Alcohol (شراب) | Severely enhances vasodilation and blood pressure lowering — dangerous risk of sudden collapse and fainting; avoid completely |
Storage Instructions
- Store below 25°C in a cool, dry place
- Protect from light, heat, and moisture — Glyceryl Trinitrate is highly sensitive to heat and light degradation
- Keep in original airtight container — GTN evaporates and loses potency if exposed to air
- Never store in the bathroom or near heat sources
- Keep out of reach of children (بچوں کی پہنچ سے دور رکھیں)
- Do not use after the expiry date printed on the pack
- Do not transfer tablets to a different container — original packaging preserves potency
Frequently Asked Questions (FAQs)
Q: Can I use Sustac 6.4mg during an acute angina attack? No — Sustac is a sustained-release tablet for long-term angina prevention, not for acute attacks; always keep a fast-acting GTN sublingual tablet or spray with you at all times for sudden chest pain episodes.
Q: Why must I never take Sustac with Viagra or similar medicines? PDE-5 inhibitors like Sildenafil (Viagra) combined with any nitrate cause a catastrophic and potentially fatal drop in blood pressure — this combination is absolutely contraindicated and must never be taken within 24 to 48 hours of each other.
Q: Why does Sustac 6.4mg cause headaches? Headache is the most common side effect of GTN — caused by blood vessel dilation in the brain; it usually improves significantly after the first few weeks of treatment as the body adjusts to the medicine.
Q: What is nitrate tolerance and how is it prevented? Nitrate tolerance occurs when the body becomes less responsive to GTN with continuous use — it is prevented by maintaining a daily nitrate-free interval of 8 to 12 hours, usually overnight, as specifically prescribed by your cardiologist.
Medical Disclaimer: This information is for general awareness only and does not replace advice from your doctor or pharmacist. Sustac 6.4mg is a prescription cardiovascular medicine — never start, stop, or adjust the dose without consulting your healthcare provider. Always keep a fast-acting GTN preparation available for acute angina attacks. Never combine with PDE-5 inhibitors under any circumstances.