Drug Class: Xanthine Oxidase Inhibitor | Urate-Lowering Agent | Form: Oral Tablet | Prescription Status: Prescription Only (Rx) — DRAP Registered
What is Zyloric 300mg Tablet?
Zyloric 300mg contains Allopurinol — the most widely prescribed and clinically established urate-lowering medicine in the world — used for the long-term management and prevention of conditions caused by elevated uric acid levels (hyperuricaemia / یورک ایسڈ کی زیادتی). Allopurinol is a xanthine oxidase inhibitor — it blocks the enzyme responsible for converting purines into uric acid in the liver and intestines, reducing the body's uric acid production at its metabolic source. By maintaining consistently lower uric acid levels over time, Allopurinol prevents the deposition of urate crystals in joints that causes the excruciatingly painful attacks of gout (گنٹھیا), the formation of urate kidney stones, and the dangerous uric acid accumulation associated with cancer chemotherapy. Zyloric 300mg is a long-term preventive medicine — not a treatment for acute gout attacks — and must be taken consistently every day to maintain urate-lowering benefit, always alongside adequate hydration and dietary modification.
What is Zyloric 300mg Used For?
- Gouty arthritis — long-term prevention of acute gout attacks and reduction of serum uric acid in patients with recurrent gout (گنٹھیا کی روک تھام)
- Hyperuricaemia — lowering chronically elevated uric acid levels in the blood regardless of cause (یورک ایسڈ کی زیادتی)
- Uric acid kidney stones — prevention of urate nephrolithiasis in patients with recurrent uric acid kidney stones (گردے کی پتھری کی روک تھام)
- Calcium oxalate kidney stones — prevention of recurrent calcium oxalate stones in patients with hyperuricosuria
- Chemotherapy-induced hyperuricaemia — preventing tumour lysis syndrome and dangerous uric acid accumulation during chemotherapy for leukaemia, lymphoma, and solid tumours
- Chronic tophaceous gout — reducing tophus size and preventing new tophi formation through sustained urate lowering
- Uric acid nephropathy — protecting kidney function from the damaging effects of chronic urate deposition in the renal tubules
How Does Zyloric 300mg Work?
Xanthine Oxidase Inhibition — Blocking Uric Acid Production: Uric acid is the final breakdown product of purines — nitrogen-containing compounds found in the body's own DNA and RNA and in purine-rich foods such as red meat, organ meats, shellfish, and alcohol. The enzyme xanthine oxidase catalyses the final two steps of purine metabolism — converting hypoxanthine to xanthine and then xanthine to uric acid. In patients with gout and hyperuricaemia, excessive uric acid production or reduced renal excretion causes serum urate levels to rise above the saturation threshold — at which point urate crystallises as monosodium urate crystals and deposits in joints, soft tissues, and the kidneys.
Allopurinol is a structural analogue of hypoxanthine — it competitively inhibits xanthine oxidase by binding to its active site, preventing both metabolic steps that produce uric acid. Allopurinol's active metabolite Oxypurinol provides additional prolonged xanthine oxidase inhibition — extending the urate-lowering effect well beyond Allopurinol's own short plasma half-life. By blocking uric acid production at its source, Allopurinol reduces serum urate levels progressively over weeks — eventually dissolving existing microcrystal deposits in joints and soft tissues, preventing new crystal formation, and reducing the frequency and severity of gout attacks over time.
Why Allopurinol Does Not Treat Acute Gout Attacks: Paradoxically, starting Allopurinol or changing its dose during an acute gout attack can worsen or prolong the attack — by mobilising urate crystals from existing deposits and causing a transient inflammatory flare. This is why Allopurinol is always started after an acute attack has fully resolved, usually with a prophylactic colchicine or NSAID cover for the first 3 to 6 months of treatment.
Dosage and Administration
⚠️ Always take exactly as prescribed by your doctor. Never start during an acute gout attack. Always take after food. Maintain excellent hydration throughout treatment — drink at least 2 litres of water daily.
| Indication | Usual Starting Dose | Frequency | Usual Maintenance Dose |
|---|---|---|---|
| Mild gout / hyperuricaemia | 100mg | Once daily | 100–300mg daily |
| Moderate gout | 300mg | Once daily | 300mg daily |
| Severe tophaceous gout | 300mg | Once daily | 300–600mg daily (divided) |
| Chemotherapy hyperuricaemia | 600–800mg | Once daily (divided) | For 2–3 days before and during chemotherapy |
| Uric acid kidney stones | 100–300mg | Once daily | Based on urine urate levels |
| Kidney impairment (eGFR 10–20) | 100mg | Every other day or less | Under specialist supervision |
Critical Dosing Rules:
- Never start Zyloric during an acute gout attack — starting urate-lowering therapy during an acute attack prolongs and worsens it; always wait until the acute attack has completely resolved before initiating or changing the dose
- Always start at 100mg and increase gradually — starting at 300mg immediately increases the risk of triggering a gout flare from crystal mobilisation; increase the dose by 100mg every 2 to 4 weeks based on serum urate levels
- Always prescribe prophylactic anti-inflammatory cover — Colchicine 0.5mg once or twice daily or a low-dose NSAID should be co-prescribed for the first 3 to 6 months to prevent gout flares during urate-lowering initiation
- Serum uric acid target is below 360 micromol/L (6mg/dL) for most patients — below 300 micromol/L for severe tophaceous gout; dose should be titrated to achieve and maintain this target
- Kidney function must be assessed before starting — Allopurinol and its metabolite Oxypurinol are renally excreted; significant dose reduction is required in kidney impairment to avoid dangerous toxicity
- Maintain excellent hydration — drink at least 2 litres of water daily to maintain adequate urine output and prevent Allopurinol crystal deposition in the urinary tract
- Zyloric is a lifelong medicine in most patients — stopping treatment allows uric acid to rise again within weeks; never stop without discussing with your doctor
How to Take:
- Swallow the tablet whole with a full glass of water
- Always take after food — significantly reduces nausea and gastrointestinal irritation
- Take at the same time each day — consistent once-daily dosing maintains stable Allopurinol and Oxypurinol blood levels
- Drink at least 2 litres of fluid daily throughout treatment — adequate hydration is essential for safe Allopurinol use
- If a dose is missed, take it as soon as remembered the same day — skip if it is the next day; never double the dose
Active Ingredients
| Ingredient | Strength per Tablet |
|---|---|
| Allopurinol | 300mg |
Who Should NOT Take Zyloric 300mg?
Do not take if you:
- Are allergic to Allopurinol or any ingredient in the tablet
- Are currently experiencing an acute gout attack — wait until the attack has completely resolved
- Have severe kidney disease without specialist dose adjustment — Oxypurinol accumulation causes serious toxicity in severe renal impairment
- Are taking Azathioprine or Mercaptopurine without dose reduction — life-threatening interaction
Always consult your doctor before taking Zyloric if you have:
- Any degree of kidney disease (گردے کی بیماری) — dose reduction based on eGFR is essential; never use standard doses in kidney impairment
- Liver disease (جگر کی بیماری) — monitor liver function during treatment
- Heart failure (دل کی کمزوری) — fluid management is important alongside Allopurinol treatment
- Hypertension (ہائی بلڈ پریشر) — ensure blood pressure is well controlled; avoid Thiazide diuretics which raise uric acid
- Are taking Azathioprine, Mercaptopurine, or Ciclosporin — critical dose adjustment required
- Are taking Warfarin or anticoagulants — Allopurinol enhances anticoagulant effect
- Are taking Ampicillin or Amoxicillin — significantly increased skin rash risk
- Are of Han Chinese, Thai, or Korean ethnicity — HLA-B*5801 genetic testing is recommended before starting Allopurinol due to very high risk of severe skin reactions in these populations
- Are pregnant or breastfeeding — use only when clearly necessary under specialist supervision
Side Effects
Common Side Effects:
- Skin rash — most common side effect; usually mild maculopapular rash; stop immediately if any rash develops as it can progress to life-threatening severe reactions
- Nausea or stomach discomfort — reduced by always taking after food
- Gout flare during initiation — paradoxical worsening or new gout attack during the first weeks of treatment from crystal mobilisation; prevented by prophylactic Colchicine or NSAID cover
- Headache — mild and usually temporary
- Drowsiness or dizziness — mild; avoid driving until individual response is established
- Altered liver enzymes — usually asymptomatic; monitor with regular blood tests
Serious Side Effects — Stop Taking and Seek Medical Help Immediately:
⚠️ Critical Safety Warning — Allopurinol Hypersensitivity Syndrome: Allopurinol hypersensitivity syndrome is a rare but potentially life-threatening reaction — risk is highest in patients with kidney impairment, those on Thiazide diuretics, and those of Han Chinese, Thai, or Korean ethnicity carrying the HLA-B*5801 allele. Any skin rash — however mild — must prompt immediate discontinuation and medical review.
- Severe cutaneous adverse reactions (SCARs) — Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) — widespread painful blistering and peeling of skin and mucous membranes; potentially fatal; stop immediately and seek emergency care (طبی ہنگامی صورتحال)
- Allopurinol hypersensitivity syndrome — fever, widespread rash, lymphadenopathy, liver damage, kidney failure, and blood disorders occurring together — life-threatening multi-organ reaction; stop immediately and seek emergency care
- Drug reaction with eosinophilia and systemic symptoms (DRESS) — widespread rash, fever, lymph node swelling, and internal organ involvement — serious and potentially fatal; stop immediately
- Severe liver toxicity — yellowing of skin or eyes (یرقان), dark urine, extreme fatigue — stop immediately and seek urgent medical attention
- Severe kidney toxicity — significantly reduced urination, extreme fatigue, severe ankle swelling — Oxypurinol accumulation in kidney impairment; stop immediately
- Severe allergic reaction — swelling of face, lips, tongue or throat, difficulty breathing (یہ طبی ہنگامی صورتحال ہے)
- Serious blood disorders — agranulocytosis, aplastic anaemia — rare; fever, unusual bruising, extreme fatigue; seek urgent haematological evaluation
- Peripheral neuropathy — numbness, tingling, or weakness in hands and feet — rare; stop and seek neurological evaluation
Drug Interactions
| Medicine / Substance | Possible Interaction |
|---|---|
| Azathioprine / Mercaptopurine | Most critical — Allopurinol dramatically increases blood levels of these immunosuppressants by blocking their metabolism; standard doses cause life-threatening bone marrow suppression; reduce Azathioprine or Mercaptopurine dose by 25 to 33% and monitor blood counts closely |
| Warfarin / anticoagulants | Allopurinol enhances anticoagulant effect — monitor INR closely at initiation and dose changes; significant bleeding risk |
| Ciclosporin | Allopurinol increases Ciclosporin blood levels — nephrotoxicity and toxicity risk; monitor Ciclosporin levels and kidney function closely |
| Ampicillin / Amoxicillin | Significantly increased risk of skin rash — avoid combining Allopurinol with aminopenicillin antibiotics wherever possible |
| Thiazide diuretics (e.g., Hydrochlorothiazide) | Raise uric acid levels and increase Allopurinol hypersensitivity risk — avoid combining; use loop diuretics if diuretic therapy is needed |
| ACE inhibitors (e.g., Captopril, Enalapril) | Increased Allopurinol hypersensitivity risk particularly with Captopril — monitor for skin reactions closely |
| Theophylline | Allopurinol inhibits Theophylline metabolism — Theophylline blood levels rise; reduce Theophylline dose and monitor levels |
| Probenecid | Increases renal excretion of Oxypurinol — may reduce the duration of Allopurinol's urate-lowering effect; avoid combining |
| Didanosine (HIV medicine) | Allopurinol significantly increases Didanosine blood levels — serious toxicity risk; avoid combination |
| Antidiabetic medicines (e.g., Chlorpropamide) | Allopurinol reduces renal clearance of Chlorpropamide — prolonged hypoglycaemia risk |
| Alcohol (شراب) | Raises uric acid levels by increasing purine metabolism and reducing urate excretion — directly counteracts Allopurinol's urate-lowering effect; avoid completely |
Storage Instructions
- Store below 25°C in a cool, dry place
- Protect from moisture and direct sunlight
- Keep in original blister pack until use
- Keep out of reach of children (بچوں کی پہنچ سے دور رکھیں)
- Do not use after the expiry date printed on the pack
Frequently Asked Questions (FAQs)
Q: Why did my gout get worse when I first started Zyloric 300mg? Paradoxical gout flares in the first weeks of Allopurinol treatment are common — caused by mobilisation of existing urate crystals from joint deposits as serum urate levels fall; this is why prophylactic Colchicine or a low-dose NSAID should always be co-prescribed for the first 3 to 6 months of Allopurinol treatment.
Q: Can I stop taking Zyloric 300mg once my uric acid level is normal? Never stop without your doctor's advice — normal uric acid readings confirm the medicine is working; stopping allows uric acid to rise again within weeks and gout attacks and crystal deposits will return; Allopurinol is a lifelong treatment in most patients with recurrent gout.
Q: What should I do immediately if I develop any skin rash while taking Zyloric? Stop taking Zyloric immediately and contact your doctor the same day — any skin rash with Allopurinol must be treated as potentially serious; mild rashes can progress rapidly to life-threatening Stevens-Johnson syndrome particularly in patients with kidney impairment or those of Han Chinese, Thai, or Korean ethnicity.
Q: Why must I drink so much water while taking Zyloric 300mg? Adequate hydration — at least 2 litres of water daily — maintains sufficient urine output to prevent Allopurinol and urate crystal deposition in the kidneys and urinary tract, reduces the risk of kidney stone formation, and supports the safe renal excretion of Allopurinol's metabolite Oxypurinol.
Medical Disclaimer: This information is for general awareness only and does not replace advice from your doctor or pharmacist. Zyloric 300mg is a prescription urate-lowering medicine — never start, stop, or adjust the dose without consulting your healthcare provider. Stop immediately and seek medical care if any skin rash develops. Regular serum uric acid, kidney function, and liver enzyme monitoring is essential throughout treatment.