American Board of Internal Medicine (ABIM) Certification Practice Exam

As chronic kidney disease (CKD) progresses to stage 4, thiazide diuretics lose potency due to the reduced ability of the kidneys to filter and excrete medications effectively. In early stages of kidney disease, thiazide diuretics can still provide effective diuresis because there is a sufficient glomerular filtration rate (GFR) to facilitate their action. However, as CKD advances and GFR declines significantly, the efficacy of thiazide diuretics diminishes.

In stage 4 CKD, the kidneys are compromised to the point where there is inadequate renal perfusion and filtration, which limits the diuretic's ability to promote sodium and water excretion. This reduced effectiveness necessitates the consideration of alternative diuretics, such as loop diuretics, which maintain potency even in advanced renal impairment.

Thus, the correct understanding is that as CKD progresses to a later stage, the pharmacological actions of thiazide diuretics are significantly impaired, leading to their loss of potency in effectively managing fluid overload or hypertension in these patients.