Antihyperuricemic agents include uricosurics (probenecid), which reduce the serum urate concentration by enhancing renal excretion of uric acid, xanthine oxidase inhibitors (allopurinol and febuxostat), which inhibit uric acid synthesis by inhibiting xanthine oxidase, the final enzyme involved in the production of uric acid, and uricase (pegloticase), which converts uric acid into allantoin.
- Urate-lowering therapy should maintain the serum uric acid level less than 6 mg/dL.
- Allopurinol should be started at a low dose and titrated up to effect.
- Febuxostat is an alternative for patients who fail to respond to or tolerate allopurinol.
- Pegloticase should not be used in patients with G6PD deficiency.
Indications for using xanthine oxidase inhibitors: in patients with recurrent gout:
- Urate overproduction (uric acid >800 mg in 24-hour urine collection on a regular diet).
- Renal insufficiency (creatinine clearance <50 mL/min).
- Hyperuricemia with nephrolithiasis of any type.
- Prophylaxis against tumor lysis syndrome.
- Hypoxanthine phosphoribosyltransferase (HPRT) deficiency (Lesch–Nyhan syndrome).
- Hyperuricemia attributable to myeloproliferative disorders.
- Serum urate >12.0 mg/dL or 24-hour urine uric acid >1100 mg.
Major Toxicities of Allopurinol: Common (rarely serious) Acute gouty arthritis, Maculopapular erythematous rash , Nausea, Diarrhea, Abnormal liver-associated enzymes, Headache, Cataracts Uncommon (potentially serious) Toxic epidermal necrolysis, exfoliative dermatitis Oxipurinol xanthine nephrolithiasis Allopurinol hypersensitivity syndrome, Cataracts, Bone marrow suppression Sarcoid-like reaction, Hepatitis Alopecia, Vasculitis Lymphadenopathy, Peripheral neuropathy Fever Renal failure (interstitial nephritis)