Does Zyloprim Treat Kidney Stones?
Zyloprim (allopurinol) prevents uric acid kidney stones by lowering uric acid levels in urine, which form when uric acid crystallizes. It does not dissolve existing stones but reduces recurrence risk, especially in patients with gout or high uric acid.[1]
How Does Allopurinol Work for Uric Acid Stones?
Allopurinol inhibits xanthine oxidase, an enzyme that produces uric acid. By blocking this, it cuts uric acid production by 30-50%, making urine less supersaturated with uric acid crystals. Guidelines from the American Urological Association recommend it for patients with recurrent uric acid stones or hyperuricosuria.[2][3]
What Types of Kidney Stones Does It Help With?
It targets only uric acid stones (5-10% of cases), which are radiolucent on X-rays and linked to low urine pH or high purine diets. It has no effect on calcium oxalate (most common, 80%), calcium phosphate, struvite, or cystine stones.[1][2]
When Do Doctors Prescribe It for Stones?
Typically for:
- History of uric acid stones confirmed by stone analysis or 24-hour urine test showing >800 mg/day uric acid.
- Gout patients prone to stones (20-25% risk).
- Combined with urine alkalinizers like potassium citrate to raise pH above 6.5.[3]
Not first-line for all stones; starts after confirming uric acid type.
Common Side Effects and Risks
Rash (2%), nausea, diarrhea. Rare but serious: severe hypersensitivity (Stevens-Johnson syndrome, higher risk in HLA-B*5801 carriers, especially Asians). Kidney function must be monitored; avoid in acute gout attacks. Drug interactions include azathioprine and mercaptopurine.[1][4]
Alternatives If Allopurinol Isn't Suitable
- Potassium citrate or sodium bicarbonate to alkalinize urine (first-line for uric acid stones).
- Febuxostat (Uloric) for those intolerant to allopurinol—similar mechanism but costlier.
- Lifestyle: high fluid intake (>2.5L/day), low-purine diet (limit meat, seafood).[2][3]
Dosage and Monitoring for Stones
Usual start: 100-300 mg/day, titrated to keep serum uric acid <6 mg/dL and urine uric acid <600 mg/day. Requires baseline CBC, liver/kidney tests, repeated every 3-6 months.[4]
[1]: Drugs.com - Zyloprim
[2]: American Urological Association - Medical Management of Kidney Stones
[3]: UpToDate - Uric Acid Nephrolithiasis
[4]: Medscape - Allopurinol Dosing