Which medication is most likely responsible for a gout attack in a patient taking multiple medications including chlorthalidone?

Chlorthalidone is a thiazide diuretic that is known to increase uric acid levels in the body, which can precipitate a gout attack. In patients with impaired renal clearance or metabolic abnormalities, this increased uric acid can lead to hyperuricemia, a condition associated with the formation of urate crystals in joints, triggering painful gout flares.

Although diuretics like chlorthalidone are effective in managing hypertension and fluid retention, they have the side effect of promoting the reabsorption of uric acid in the kidneys. This mechanism is what makes chlorthalidone the medication most likely responsible for a gout attack in a patient already at risk for gout.

Other medications listed, such as amlodipine (a calcium channel blocker), acetazolamide (a carbonic anhydrase inhibitor), and lisinopril (an ACE inhibitor), do not have a significant impact on uric acid levels in the same way that chlorthalidone does, making them less likely to be involved in precipitating a gout attack. This establishes chlorthalidone as the most probable cause of a gout flare in this clinical scenario.