When to Recheck Uric Acid After Starting Allopurinol
Serum uric acid levels should be rechecked every 2-4 weeks during the initial dose titration phase of allopurinol therapy until the target level of <6 mg/dL is achieved. 1
Initial Titration Phase Monitoring
Check serum uric acid every 2-4 weeks while actively titrating the allopurinol dose upward until reaching the target of <6 mg/dL (360 μmol/L) 1
This frequent monitoring during titration is essential to implement the treat-to-target strategy rather than using fixed standard doses 1
For patients with severe gout (tophi, chronic arthropathy, frequent attacks), target a lower serum uric acid of <5 mg/dL (300 μmol/L) until complete crystal dissolution occurs 1
The American College of Rheumatology recommends starting at ≤100 mg daily for patients with normal renal function, increasing by 100 mg increments every 2-4 weeks 1
After Achieving Target Levels
Once stable target serum uric acid levels are achieved and gout is well-controlled, recheck serum uric acid every 6 months to ensure maintenance below 6 mg/dL 2
Regular monitoring remains essential even after achieving control, as approximately 40% of successfully treated patients show recurrence of flares after changes in urate-lowering therapy 2
Renal function should also be monitored every 6 months, as changes may necessitate allopurinol dose adjustments 2
Expected Timeline for Response
Administration of allopurinol generally results in a fall in both serum and urinary uric acid within 2 to 3 days 3
A week or more of treatment may be required before full effects are manifested 3
The degree of uric acid decrease is dose-dependent and can be manipulated based on monitoring results 3
Critical Pitfalls to Avoid
Do not rely solely on symptom improvement without laboratory confirmation of urate levels below target, as this leads to suboptimal outcomes 2
Inadequate monitoring after achieving initial control can miss rising urate levels that may lead to renewed crystal formation 2
In some patients with severe tophaceous gout, a dramatic fall in urinary uric acid excretion may not occur initially, possibly due to mobilization of urate from tissue deposits 3
Serum uric acid levels can be misleadingly normal or low during acute gout attacks, as uric acid behaves as a negative acute phase reactant during inflammation 4
Special Considerations for Renal Impairment
For patients with CKD stage ≥3, start at ≤50 mg daily and adjust based on renal function 1
In severely impaired renal function, the half-life of oxipurinol (allopurinol's active metabolite) is greatly prolonged, and doses as low as 100 mg per day or 300 mg twice weekly may be sufficient 3
Patients with impaired renal function should be carefully observed during early stages of therapy, with monitoring of both serum uric acid and renal function 3