A 48-year-old man comes to establish care after moving to a new state. He feels well and has no symptoms. The patient has a history of type 2 diabetes mellitus diagnosed 6 months ago; he was prescribed metformin by his previous physician but stopped taking it due to diarrhea. He was unable to follow up with the physician and has not taken any other medications. The patient exercises regularly and follows a low-carbohydrate diet. Laboratory results show a fasting blood glucose of 140 mg/dL and a hemoglobin A1c of 7.5%. The physician counsels the patient about adding canagliflozin to optimize glycemic control. Which of the following tests should be ordered prior to initiating this new medication?
Show Explanatory Sources
Sodium-glucose cotransporter-2 (SGLT-2) is a low-affinity, high-capacity transport protein that reabsorbs 90% of filtered glucose in the proximal tubule. SGLT-2 inhibitors (eg, canagliflozin, dapagliflozin) are oral antidiabetic agents that decrease renal reabsorption of sodium and glucose and thereby decrease blood glucose levels. They are used primarily as a combination therapy (eg, with metformin), especially in patients with atherosclerotic cardiovascular disease (eg, prior myocardial infarction), heart failure, or nephropathy (eg, albuminuria).
Because SGLT-2 inhibitors rely on adequate renal glucose filtration to exert their antihyperglycemic effect, they become less effective or ineffective as renal function declines (eg, when estimated glomerular filtration rate [eGFR] falls <30-45 mL/min/1.73 m2). Therefore, checking serum creatinine (used to calculate eGFR) is recommended prior to medication initiation.
(Choices A and E) Although SGLT-2 inhibitors increase the risk for genitourinary infections (eg, candidiasis, urinary tract infection), screening for infection with a leukocyte count and urinalysis in asymptomatic patients (eg, no dysuria or fever) is unnecessary.
(Choice C) Certain drugs such as diuretics (eg, thiazide, loop) reduce renal uric acid clearance and may precipitate gout. However, SGLT-2 inhibitors are associated with increased renal uric acid clearance and are not expected to increase the risk for gout.
(Choice D) Thyroid function tests are routinely performed on patients taking lithium and amiodarone, which can alter thyroid hormone metabolism. However, thyroid function tests are not required for antidiabetic medications.
Educational objective:
Sodium-glucose cotransporter-2 inhibitors (eg, canagliflozin, dapagliflozin) lower glucose levels by decreasing renal reabsorption of glucose and have cardioprotective and renoprotective effects. Checking serum creatinine is recommended prior to initiation because the antihyperglycemic effect of these medications becomes less pronounced as renal function declines.