Allopurinol Side Effects in Kids: What Parents Need to Know

When a child is prescribed allopurinol, a medication used to lower uric acid levels in conditions like gout or kidney stones caused by high uric acid. Also known as Zyloprim, it's sometimes used in kids with leukemia, certain genetic disorders, or recurrent kidney stones. It’s not a common drug for children, but when it’s needed, knowing what to watch for can make all the difference.

One of the biggest concerns with allopurinol in kids is a rare but serious skin reaction called Stevens-Johnson syndrome or toxic epidermal necrolysis. These aren’t just rashes—they’re life-threatening conditions that start with flu-like symptoms, then blistering skin and peeling. Kids with the HLA-B*5801 gene variant are at higher risk, and testing for it before starting allopurinol is becoming more common in pediatric care. If your child gets a fever, sore throat, or a red, painful rash within the first few weeks, don’t wait—get them to a doctor immediately.

Less severe but still common side effects include nausea, vomiting, diarrhea, and drowsiness. Some kids may also develop mild liver enzyme changes or joint pain. These often settle down as their body adjusts, but if symptoms stick around or get worse, talk to your pediatrician. It’s also important to keep your child well-hydrated while on this medication—dehydration can raise the risk of kidney stones, which allopurinol is meant to prevent, not cause.

Another thing parents often miss: allopurinol doesn’t work right away. It can take weeks to lower uric acid levels enough to prevent flare-ups. That’s why it’s sometimes started after a flare has already cleared up. If your child is on allopurinol for a condition like Lesch-Nyhan syndrome or tumor lysis syndrome, the goal isn’t quick relief—it’s long-term protection. Regular blood tests to check kidney function and uric acid levels are part of the routine.

Some kids on allopurinol also get prescribed colchicine or NSAIDs like ibuprofen to prevent flare-ups during the first few months. This isn’t because allopurinol isn’t working—it’s because the body is adjusting. Think of it like a thermostat turning on and off before it finds the right temperature. Your doctor knows this and will likely have a plan.

What’s not talked about enough is how often allopurinol gets mixed up with other gout meds like febuxostat or probenecid. In kids, it’s usually the first choice because it’s been studied longer and has a clearer safety track record than newer drugs. But if your child has a bad reaction, alternatives exist. The key is catching side effects early.

You’re not alone in wondering if this medication is worth the risk. Many parents feel the same. But for kids with chronic high uric acid, the risks of not treating it—like permanent kidney damage or repeated hospital visits—are often worse. The goal isn’t to scare you. It’s to help you spot the warning signs so you can act fast if something’s off.

Below, you’ll find real-world comparisons and case-based guides from other parents and doctors who’ve walked this path. You’ll see what side effects showed up in actual kids, how they were handled, and what worked best in different situations. No fluff. Just what you need to know to keep your child safe.