Allopurinol

Bone marrow suppression has been reported in patients receiving allopurinol, most of whom received concomitant medications with a potential for hematologic toxicity. The onset occurs between 6 weeks to 6 years after allopurinol initiation. Varying degrees of bone marrow depression affecting one or more cell lines may occur (rare) in patients receiving allopurinol alone.

May occasionally cause drowsiness; patients must be cautioned about performing tasks that require mental alertness (eg, operating machinery or driving).

Cases of hepatotoxicity (reversible) have been reported. Asymptomatic elevations of serum alkaline phosphatase or serum transaminases have been observed. Monitor for signs/symptoms of hepatotoxicity and evaluate liver function if they occur. Periodic liver function tests are recommended during the early stages of therapy in patients with preexisting hepatic impairment.

Allopurinol has been associated with hypersensitivity reactions. In some instances a skin rash may be followed by more severe hypersensitivity reactions, including exfoliative, urticarial, and purpuric lesions, Stevens-Johnson syndrome, generalized vasculitis, and/or hepatotoxicity (irreversible); some reactions have been fatal (rare). Discontinue at first sign of skin rash or other signs indicative of allergic reaction. Consider HLA-B*5801 testing in patients at a higher risk for allopurinol hypersensitivity syndrome (eg, Korean patients with stage 3 or worse CKD and Han Chinese and Thai descent regardless of renal function) prior to initiation of therapy (ACR guidelines [Khanna 2012]). Disease-related concerns:

Even when normal or subnormal serum uric acid levels have been attained, an increase in acute gout attacks has been reported during the early stages of allopurinol administration. When allopurinol is initiated, maintenance colchicine doses should generally be administered as prophylaxis. Additionally, it is recommended to initiate with a low allopurinol dose (100 mg daily) and increase at weekly intervals by 100 mg until a serum uric acid level of 6 mg/dL or less is attained (do not exceed the maximum recommended dose of 800 mg/day). In some cases, colchicine or anti-inflammatory agents may be required to suppress gouty attacks. After several months of therapy, attacks usually decrease in duration and severity. These episodes may be due to mobilization of urates from tissue deposits, causing fluctuations in the serum uric acid levels. Even with adequate allopurinol therapy, several months may be required to deplete the uric acid pool enough to achieve control of the acute attacks.

Dose reductions are recommended in patients with renal impairment; monitor closely. Patients with reduced renal function receiving thiazide diuretics in combination with allopurinol may be at increased risk for hypersensitivity reactions. Some patients with pre-existing renal disease or poor urate clearance have shown a rise in BUN with allopurinol. Patients with renal impairment should be carefully monitored during the early stages of allopurinol treatment; reduce the dose or withdraw therapy if increased renal function abnormalities appear and persist. Renal failure associated with allopurinol has been observed in patients with hyperuricemia secondary to neoplastic diseases. Concurrent conditions including multiple myeloma and congestive myocardial disease were present among patients whose renal dysfunction increased after allopurinol was begun. Renal failure is also frequently associated with gouty nephropathy and rarely with hypersensitivity reactions associated with allopurinol. Albuminuria has been observed among patients who developed clinical gout following chronic glomerulonephritis and chronic pyelonephritis. Concurrent drug therapy issues:

Potentially significant drug interactions may exist, requiring dose or frequency adjustment, additional monitoring, and/or selection of alternative therapy. Consult drug interactions database for more detailed information.

Concomitant use of allopurinol (at doses of 300 to 600 mg/day) with mercaptopurine or azathioprine will require a reduction in the mercaptopurine or azathioprine dose to approximately one-third to one-fourth of the usual dose. Subsequent dose adjustments may be necessary based on therapeutic response and toxicity. Other warnings/precautions:

Do not use to treat asymptomatic hyperuricemia.

Fluid intake sufficient to yield a daily urinary output of at least 2 L and maintenance of a neutral or (preferably) a slightly alkaline urine are desirable in order to avoid possible formation of xanthine calculi due to allopurinol therapy and to help prevent renal urate precipitation in patients receiving concomitant uricosuric agents.