A 71-year-old man is evaluated for severe tophaceous gout. Colchicine has been effective in reducing flares to approximately two in the past year. On initial evaluation 1 year ago, serum urate level was 10.2 mg/dL (0.60 mmol/L). Allopurinol was initiated but subsequently discontinued because of gastrointestinal intolerance. He was switched to febuxostat, which was increased to maximum dose without success in reaching the serum urate goal of less than 6.0 mg/dL (0.35 mmol/L). He recently had a gout flare of his right great toe, which has nearly resolved.
On physical examination, temperature is 36.6 °C (97.9 °F), blood pressure is 140/80 mm Hg, pulse rate is 89/min, and respiration rate is 15/min. BMI is 32. Bulky tophi are present over bilateral elbows, hands, and feet with drainage of pasty material from a large tophus over the second metacarpophalangeal joint of the left hand. There are mild swelling and tenderness to palpation over the right first metatarsophalangeal joint.
Laboratory studies reveal a serum urate level of 10.9 mg/dL (0.64 mmol/L), an estimated glomerular filtration rate of 42 mL/min/1.73 m2, and a normal glucose-6-phosphate dehydrogenase level.
Which of the following is the most appropriate next step in management?