What is allopurinol?
Allopurinol (brand name Zyloprim) is the most widely prescribed medication for lowering uric acid in people with gout. It belongs to a class of drugs called xanthine oxidase inhibitors — it works by blocking the enzyme your body uses to produce uric acid, reducing the amount of uric acid in your blood.
Allopurinol is a long-term prevention medication, not a treatment for acute gout flares. Think of it this way: colchicine and NSAIDs put out the fire; allopurinol turns off the gas. The goal is to lower your uric acid level below 6 mg/dL, which allows existing uric acid crystals to slowly dissolve and prevents new ones from forming.
How to take it
- Once daily, usually in the morning, with or without food
- Start low: most patients begin at 100 mg per day (sometimes 50 mg if kidney function is reduced)
- Increase gradually: your doctor will raise the dose every 2–4 weeks, guided by uric acid blood levels
- Target: uric acid below 6 mg/dL (sometimes below 5 mg/dL for patients with tophi)
- Most patients end up on 300–400 mg daily, though some need higher doses (up to 800 mg)
Do not start allopurinol during an active gout flare. Wait until the flare has fully resolved before beginning. Starting during a flare can make it worse.
What to expect when starting
Here is the most important thing to understand about allopurinol: starting it can temporarily trigger gout flares. This is a well-known paradox and does not mean the medication is making your gout worse.
When uric acid levels change — even when they drop in the right direction — existing crystals can shift and provoke inflammation. This is why your doctor will prescribe prophylactic colchicine or an NSAID for the first 3–6 months alongside allopurinol.
It takes several months of consistent therapy for uric acid to reach target and for crystal deposits to begin dissolving. Full benefit may take 6–12 months or longer, especially if you have tophi. Patience is essential.
Lab monitoring
Regular blood work is important while taking allopurinol:
- Uric acid level — checked every few weeks during dose titration, then every 6–12 months once at target
- Kidney function (creatinine/BUN) — periodically
- Liver function tests (LFTs) — periodically
- Complete blood count (CBC) — if clinically indicated
Side effects to watch for
Common:
- Gout flares during dose titration — expected and manageable with prophylaxis (see above)
- Rash (mild) — stop allopurinol and call us immediately. Most rashes are benign, but any rash needs evaluation because it can rarely be the first sign of a serious reaction.
- GI upset — nausea or diarrhea, usually mild
Serious but rare:
Allopurinol hypersensitivity syndrome (AHS/DRESS) is a rare but potentially life-threatening reaction that typically occurs in the first few months of treatment. Symptoms include rash, fever, liver and kidney problems, and abnormal blood counts. This is why any rash while on allopurinol should be reported immediately — early recognition is critical.
Who is at higher risk for AHS?
Certain genetic variants increase the risk, particularly the HLA-B*5801 allele, which is more common in people of:
- Southeast Asian descent (Thai, Korean, Han Chinese)
- African American descent
Your doctor may recommend HLA-B*5801 testing before starting allopurinol if you belong to one of these groups. If you carry this allele, an alternative medication (such as febuxostat) is safer.
Things to avoid
- Do not stop and restart allopurinol frequently. Gaps in therapy increase the risk of hypersensitivity reactions and flares. Once you start, take it consistently every day — even when you feel fine.
- Azathioprine (Imuran) and mercaptopurine — allopurinol dramatically increases levels of these drugs, causing dangerous toxicity. If you take either of these, your doctor must know.
- Alcohol — does not directly interact with allopurinol, but beer and liquor raise uric acid levels, working against the medication.
Frequently asked questions
If allopurinol prevents gout, why am I still getting flares? Flares during the first several months are common and expected as your body adjusts to changing uric acid levels. This does not mean the medication has failed. Keep taking it, use your prophylactic colchicine or NSAID, and report flares to us so we can manage them.
How long do I need to take allopurinol? For most people, allopurinol is a lifelong medication. Gout is a chronic condition caused by uric acid overproduction or underexcretion. Stopping allopurinol allows uric acid to rise again and flares to return.
Can I take allopurinol if I have kidney disease? Yes, but the starting dose is typically lower. Older guidelines recommended strict dose caps based on kidney function, but current evidence supports titrating to the uric acid target with careful monitoring, even in patients with reduced kidney function. Your doctor will adjust the approach to your situation.
My uric acid is normal now. Can I stop taking allopurinol? Your uric acid is normal because you are taking allopurinol. Stopping it will cause levels to rise again. Think of it like blood pressure medication — it works as long as you take it.
Do I need to change my diet if I am on allopurinol? Allopurinol is far more effective than dietary changes alone at lowering uric acid. That said, reducing high-purine foods (organ meats, shellfish), limiting alcohol (especially beer), and staying well-hydrated are still good practices that support your overall health.
This handout is for informational purposes only and does not replace the advice of your physician. Always follow your doctor’s specific instructions about your medications. If you have questions or concerns, contact Synergy Rheumatology & Wellness.