Nursing care
Allopurinol: what to check before you give it
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated September 2026
Short answer
Allopurinol lowers uric acid by blocking the enzyme that produces it, used to prevent gout attacks and manage chronic hyperuricaemia. It is started only after an acute gout attack has settled, never during one, and is given with plenty of fluid while any rash is reported immediately.
Mechanism, simply
Allopurinol inhibits xanthine oxidase, the enzyme that converts purines into uric acid. Less uric acid is produced, serum levels fall over weeks, and the urate crystals that cause gout have less material to accumulate from.
It does not treat pain or inflammation, and it does not work quickly. Because it lowers urate gradually, it can actually mobilise crystals from existing deposits during the first weeks of treatment and trigger a flare, which is the reason for the timing rule that runs through every other section on this page.
Indications you will see on the ward
Allopurinol is used for chronic gout prophylaxis in patients with recurrent attacks, tophi, or urate nephropathy, and for hyperuricaemia related to conditions like chronic kidney disease. You will also see it started before chemotherapy in patients at risk of tumour lysis syndrome, where a sudden release of purines from dying cancer cells can spike uric acid and precipitate acute kidney injury.
It is not used for the pain of an acute attack itself; NSAIDs, colchicine, or corticosteroids cover that. Allopurinol's role is long-term urate control, and it is a maintenance drug, so patients often stay on it indefinitely once started, which is worth confirming before assuming a short course.
Assessment before administration
Confirm the patient is not in an active gout flare before starting or restarting allopurinol. Starting it during an acute attack is started after the acute gout attack has settled, never during it, because lowering urate levels while a flare is active can worsen or prolong that attack.
Check renal function before starting and periodically after, since the dose is adjusted downward in renal impairment and clearance is reduced. Ask about a history of HLA-B*5801, which is more common in certain Southeast Asian and African ancestries and raises the risk of severe skin reactions, and check baseline full blood count and liver function where the prescriber orders them.
Toxicity and the antidote
There is no specific antidote for allopurinol toxicity; management is supportive, with the drug stopped and hydration maintained to support renal clearance of accumulated purines. This is different from many drugs on the exam that pair with a named reversal agent, and that absence is itself a testable point.
The serious toxicity to watch for is allopurinol hypersensitivity syndrome, which combines a severe rash with fever, eosinophilia, and organ involvement including the liver and kidneys, and carries significant mortality if not caught early. This is why any rash is reported immediately and the drug stopped rather than watched, rather than waiting to see if it settles.
Interactions that matter
Azathioprine and 6-mercaptopurine are the interaction that matters most clinically: allopurinol blocks the enzyme that breaks them down, so combined use can cause severe, even life-threatening bone marrow suppression unless the dose of the other drug is reduced substantially, often by 65 to 75 percent, under specialist guidance.
Thiazide diuretics increase the risk of allopurinol hypersensitivity and can also impair uric acid excretion, so the combination is used cautiously. ACE inhibitors combined with allopurinol raise the risk of hypersensitivity reactions too. Allopurinol can also increase warfarin's effect, so INR is monitored more closely when the two are started or stopped together.
What the patient must be told
Tell the patient to drink plenty of fluid throughout treatment, since good hydration supports uric acid excretion and reduces the risk of urate kidney stones as levels fall. Two to three litres a day is a reasonable target unless fluid is restricted for another reason.
Warn them explicitly that a gout flare can happen in the first weeks of starting allopurinol even though the drug is working, so they should not stop it on their own if this happens, but should let their prescriber know since a low-dose anti-inflammatory or colchicine is often added to cover this period. Tell them any new rash, especially with fever or mouth sores, needs same-day medical attention, and that alcohol should be limited since it raises uric acid production and works against the drug's purpose.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our pharmacology practice questions are the closest set to what this page covers.
One question from the pharmacology set
A client with heart failure is started on furosemide 40 mg PO daily. Which findings should the nurse report to the provider before administering the next dose? Select all that apply.
Rationale
Furosemide is a loop diuretic, so the two things you are watching are potassium and kidney function. A potassium of 2.9 mEq/L is below the 3.5–5.0 reference range and puts the client at risk for dysrhythmia — hold and report. Muscle cramps with palpitations are the clinical face of that same hypokalemia, so they are reported together, not separately. A creatinine that doubles signals the diuresis has outrun renal perfusion. A blood pressure of 132/78 and a 1 kg loss are the expected response to the drug working, not reasons to hold it.
Answer: A, D, E
Common questions
Why can't allopurinol be started during a gout attack?
Because lowering uric acid while crystals are actively depositing during a flare can mobilise more crystals and worsen or prolong that attack. It is started only once the acute attack has fully settled, usually after a delay of a couple of weeks.
What does a rash on allopurinol mean?
Any rash needs immediate reporting and the drug stopped pending review, because it can be the first sign of allopurinol hypersensitivity syndrome, a rare but serious reaction involving the skin, liver, and kidneys. It is not something to wait out at home.
Can allopurinol be given with azathioprine?
Only with the azathioprine dose reduced substantially and under specialist guidance, because allopurinol blocks the enzyme that clears azathioprine and the combination can cause severe bone marrow suppression if the dose is not adjusted.
Does allopurinol treat gout pain?
No. It lowers uric acid over the long term to prevent future attacks but does nothing for the pain or inflammation of a current flare, which is managed separately with NSAIDs, colchicine, or corticosteroids.
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