Allopurinol is a cornerstone medicine for lowering uric acid and preventing gout attacks and kidney stones. The key takeaway: Allopurinol works best when started low, taken daily, and monitored properly—especially in kidney disease.
What Is Allopurinol?
Allopurinol is a xanthine oxidase inhibitor that reduces the body’s production of uric acid. By lowering uric acid levels over time, it prevents gout flares, shrinks tophi, and reduces uric-acid kidney stones.
Brand names: Zyloprim, Alloprim (IV), Apo-Allopurinol
Primary audience: Global patients, beginners, students, and clinicians-in-training
How Allopurinol Works
Uric acid is produced when purines are broken down. The enzyme Xanthine Oxidase converts hypoxanthine → xanthine → uric acid.
Allopurinol blocks this enzyme, so uric acid production falls. Lower levels mean fewer crystals in joints and kidneys.
Why this matters now: Treat-to-target urate (<6 mg/dL; <5 mg/dL in severe tophaceous gout) is the modern standard—and allopurinol remains first-line worldwide.
Indications: When Is Allopurinol Used?
- Gout (chronic management, not for acute pain relief)
- Hyperuricemia due to chemotherapy (tumor lysis syndrome prophylaxis)
- Recurrent uric acid kidney stones
- Certain enzyme disorders with high uric acid (e.g., Lesch–Nyhan)
Not for acute flares: Starting allopurinol during a flare is acceptable with anti-inflammatory cover, but it doesn’t relieve acute pain by itself.
How to Start Allopurinol Safely
Day 0–7 (Start Low)
1. Begin 100 mg once daily (or 50 mg if kidney disease).Weeks 2–8 (Titrate)
3. Increase by 100 mg every 2–4 weeks based on uric acid.
4. Typical maintenance: 300 mg/day (some need up to 800 mg/day under supervision).
Flare Prevention (First 3–6 Months)
5. Add Colchicine 0.5–0.6 mg once/twice daily or a low-dose NSAID to prevent early flares.
Monitoring
6. Check serum urate every 2–4 weeks until target, then every 6–12 months.
7. Monitor LFTs, CBC, and renal function.
Dosage Table
| Situation | Starting Dose | Typical Range |
|---|---|---|
| Normal renal function | 100 mg/day | 300–600 mg/day |
| CKD (eGFR ↓) | 50–100 mg/day | Individualized |
| Severe gout/tophi | 100 mg/day | Up to 800 mg/day (specialist) |
| IV (hospital use) | As indicated | Alloprim protocol |
Side Effects & Safety
Common (usually mild):
- Rash, nausea, diarrhea
- Headache, drowsiness
Serious (seek care immediately):
- Allopurinol Hypersensitivity Syndrome (AHS): fever, rash, liver/kidney injury, eosinophilia
- Stevens–Johnson syndrome / TEN (rare but life-threatening)
High-risk groups: CKD, older adults, high starting dose, and HLA-B*58:01 carriers (more common in Han Chinese, Thai, Korean, some Indian populations).
Best practice: Consider HLA-B*58:01 testing in high-risk ethnicities before starting therapy.
Drug Interactions You Must Know
- Azathioprine / 6‑Mercaptopurine: Reduce dose to 25% (dangerous interaction)
- Warfarin: INR may increase (monitor)
- Thiazide diuretics: ↑ rash risk
Allopurinol vs Alternatives
| Feature | Allopurinol | Febuxostat | Probenecid |
|---|---|---|---|
| First-line | ✅ Yes | Second-line | Selected cases |
| Renal disease | Adjustable | Often preferred | Less effective |
| CV safety | Neutral | CV caution in some | Neutral |
| Cost | Low | Higher | Moderate |
Bottom line: Allopurinol remains first-choice for most patients.
Common Mistakes
1. Stopping during a flare → Don’t. Continue with anti-inflammatory cover.Real-World Templates
Starter Prescription
Allopurinol 100 mg PO daily after food × 4 weeks.
Colchicine 0.6 mg PO daily × 3 months.
Check serum urate, LFTs, creatinine in 4 weeks.
Patient Advice
Take allopurinol every day, even if you feel fine. Early flares can happen—this means the medicine is working. Call us immediately if you develop a rash.
FAQs
Q1. Can allopurinol be started during an acute gout attack?
Yes—with colchicine/NSAID cover. It won’t treat pain but won’t worsen outcomes if managed properly.
Q2. How long do I need to take allopurinol?
Usually lifelong for chronic gout to keep urate at target.
Q3. Does allopurinol damage kidneys?
No. When dosed correctly, it’s kidney-safe and often kidney-protective.
Q4. What foods should I avoid?
Limit purine-rich foods (red meat, organ meats), alcohol (beer), and fructose.
Q5. What if I miss a dose?
Take it when remembered the same day; don’t double up.
Q6. Is febuxostat safer?
It’s an option if allopurinol isn’t tolerated; CV risk must be considered.
Q7. Can I stop once uric acid is normal?
No—levels rise again if stopped.
