Pharmacological Management of Diabetes

Correct Answer

C — Empagliflozin

Rationale

Empagliflozin is a sodium-glucose cotransporter-2 inhibitor, along with dapagliflozin, canagliflozin, and ertugliflozin. Sitagliptin is a dipeptidyl peptidase-4 inhibitor. Pioglitazone is a thiazolidinedione. Liraglutide is a glucagon-like peptide-1 receptor agonist.

Correct Answer

A — Sodium-glucose cotransporter-2 inhibitor

Rationale

Dapagliflozin is classified as a sodium-glucose cotransporter-2 inhibitor, working by blocking glucose reabsorption in the proximal convoluted tubule of the kidney. Glucagon-like peptide-1 receptor agonists include liraglutide and semaglutide. Dipeptidyl peptidase-4 inhibitors include sitagliptin and linagliptin. Metformin is the only biguanide in current clinical use.

Correct Answer

D — Sodium-glucose cotransporter-2 inhibitor

Rationale

Canagliflozin is classified as a sodium-glucose cotransporter-2 inhibitor. Sulfonylureas include glipizide, glyburide, and glimepiride. Alpha-glucosidase inhibitors include acarbose and miglitol. Thiazolidinediones include pioglitazone and rosiglitazone.

Correct Answer

B — Sodium-glucose cotransporter-2 inhibitor

Rationale

Ertugliflozin is classified as a sodium-glucose cotransporter-2 inhibitor, the fourth approved agent in this class alongside empagliflozin, dapagliflozin, and canagliflozin. Meglitinides include repaglinide and nateglinide. Long-acting amylin analogs include cagrilintide. Dipeptidyl peptidase-4 inhibitors include sitagliptin, saxagliptin, linagliptin, and alogliptin.

Correct Answer

A — Sodium-glucose cotransporter-2, which handles approximately 90 percent of proximal tubule glucose reabsorption in the S1 and S2 segments

Rationale

Sodium-glucose cotransporter-2 is the high-capacity, low-affinity glucose transporter responsible for approximately 90 percent of the glucose reabsorbed from the glomerular filtrate, located in the S1 and S2 segments of the proximal convoluted tubule. Sodium-glucose cotransporter-1 handles the remaining approximately 10 percent in the S3 segment and is a high-affinity, lower-capacity transporter. Glucose transporter type 2 and glucose transporter type 4 are not the targets of this drug class — glucose transporter type 2 is expressed in liver and pancreas, and glucose transporter type 4 mediates insulin-stimulated peripheral glucose uptake in muscle and adipose tissue.

Correct Answer

C — Empagliflozin

Rationale

Empagliflozin has the broadest approved indication set among sodium-glucose cotransporter-2 inhibitors, with approvals for type 2 diabetes mellitus (EMPA-REG OUTCOME), heart failure with reduced ejection fraction (EMPEROR-Reduced), heart failure with preserved ejection fraction (EMPEROR-Preserved), and chronic kidney disease (EMPA-KIDNEY). Dapagliflozin is approved for type 2 diabetes mellitus, heart failure with reduced ejection fraction, and chronic kidney disease, but not heart failure with preserved ejection fraction. Canagliflozin is approved for type 2 diabetes mellitus and chronic kidney disease only. Ertugliflozin is approved for type 2 diabetes mellitus only.

Correct Answer

B — Sodium-glucose cotransporter-2 inhibitors block proximal tubule glucose reabsorption, causing glycosuria that produces a caloric deficit contributing to weight loss, osmotic diuresis that reduces plasma volume and blood pressure, and glucose excretion that lowers blood glucose

Rationale

All three effects flow from a single mechanism: blockade of sodium-glucose cotransporter-2 in the proximal tubule forces glucose into the urine. The glycosuria creates a caloric deficit of approximately 200 to 300 kcal per day, contributing to 2 to 3 kg weight loss. The glucose in the tubular lumen creates an osmotic gradient that draws water with it, producing a mild osmotic diuresis that reduces plasma volume and lowers blood pressure by 3 to 5 mmHg systolic. And the glucose that would have been reabsorbed now remains in the blood glucose-lowering pathway in reverse — reabsorption is prevented, so blood glucose falls. Sodium-glucose cotransporter-2 inhibitors do not activate adenosine monophosphate-activated protein kinase, do not stimulate glucagon-like peptide-1 secretion from intestinal cells, and do not inhibit angiotensin-converting enzyme.

Correct Answer

D — Sodium-glucose cotransporter-2 inhibitors reduce proximal tubule sodium reabsorption, increasing sodium delivery to the macula densa, which restores tubuloglomerular feedback and reduces the glomerular hyperfiltration that drives diabetic nephropathy progression

Rationale

In diabetic nephropathy, hyperglycemia-driven upregulation of proximal tubule sodium-glucose cotransporter-2 leads to excess sodium and glucose reabsorption. Reduced sodium delivery to the macula densa disables tubuloglomerular feedback, causing afferent arteriolar dilation and glomerular hyperfiltration — a key driver of progressive nephron loss. Sodium-glucose cotransporter-2 inhibitors block the cotransporter, reducing proximal sodium reabsorption and restoring sodium delivery to the macula densa. Tubuloglomerular feedback is re-engaged, causing afferent arteriolar constriction, reducing intraglomerular pressure, and relieving hyperfiltration. This is a direct intrarenal hemodynamic effect distinct from systemic blood pressure lowering. Sodium-glucose cotransporter-2 inhibitors do not block angiotensin II receptors, do not activate peroxisome proliferator-activated receptor gamma, and do not act on glycation end-products.

Correct Answer

A — Osmotic diuresis and natriuresis from glycosuria reduce cardiac preload and volume overload, while a shift in myocardial fuel utilization toward ketone bodies — which are more oxygen-efficient than glucose — may improve cardiac energetics

Rationale

The heart failure benefit of sodium-glucose cotransporter-2 inhibitors operates through mechanisms that are largely glucose-independent, explaining why the benefit extends to patients without diabetes. Glycosuria produces osmotic diuresis and natriuresis, reducing plasma volume and cardiac preload — a hemodynamic mechanism analogous to, but distinct from, loop diuretics. Additionally, sodium-glucose cotransporter-2 inhibition raises circulating ketone body levels modestly; ketones are a preferred cardiac fuel when available and require less oxygen per unit of adenosine triphosphate produced than glucose, potentially improving the energetic efficiency of the failing heart. While cardiac sodium-hydrogen exchanger-1 inhibition has been proposed as a mechanism, this is not the established teaching-level explanation and is still under investigation. Sodium-glucose cotransporter-2 inhibitors do not directly stimulate natriuretic peptide secretion or block transforming growth factor-beta in cardiac fibroblasts as their primary mechanism.

Correct Answer

C — Glycemic efficacy depends on the amount of glucose filtered at the glomerulus; at estimated glomerular filtration rate of 22 mL/min, very little glucose reaches the tubule to be blocked, so glycosuria is minimal — but the tubuloglomerular feedback restoration and hemodynamic effects that protect the heart and kidney do not require high glucose filtration

Rationale

The glucose-lowering effect of sodium-glucose cotransporter-2 inhibitors depends entirely on the filtered glucose load — how much glucose the glomerulus delivers to the tubule for the drug to block. At an estimated glomerular filtration rate of 22 mL/min, total filtration is so reduced that very little glucose reaches the proximal tubule, and blocking sodium-glucose cotransporter-2 produces minimal glycosuria. However, the tubuloglomerular feedback mechanism — which depends on sodium delivery to the macula densa, not on glucose filtration volume — remains active even at low estimated glomerular filtration rate values. Reducing proximal sodium reabsorption still increases macula densa sodium delivery and restores tubuloglomerular feedback signaling. The hemodynamic effects (reduced intraglomerular pressure, modest volume unloading) also persist. Empagliflozin is metabolized by glucuronidation and does not accumulate to toxic levels or produce active metabolites.

Correct Answer

B — Glycosuria reduces the glucose stimulus for insulin secretion, lowering insulin levels; reduced insulin combined with increased glucagon promotes ketogenesis, producing ketoacidosis at near-normal blood glucose levels

Rationale

Euglycemic diabetic ketoacidosis is a serious adverse effect of sodium-glucose cotransporter-2 inhibitors that is dangerous precisely because the blood glucose is near-normal, making it easy to miss. The mechanism begins with glycosuria: as glucose is excreted in the urine, blood glucose falls and the glucose stimulus for pancreatic insulin secretion is reduced. Lower insulin combined with a glucagon-predominant hormonal state shifts hepatic metabolism toward ketogenesis. Meanwhile, the ongoing urinary glucose loss prevents the blood glucose from rising to levels that would be recognized as typical diabetic ketoacidosis. The result is significant ketoacid accumulation at blood glucose values that do not trigger clinical suspicion for diabetic ketoacidosis. Any patient on a sodium-glucose cotransporter-2 inhibitor who presents with nausea, vomiting, or malaise should have ketones and arterial pH checked regardless of blood glucose. Empagliflozin does not inhibit renal bicarbonate reabsorption, does not directly activate peroxisome proliferator-activated receptor alpha, and reduced renal ketone clearance is a secondary consideration rather than the mechanism of this presentation.

Correct Answer

D — Glycosuria deposits glucose in the perineal and genital area, creating a nutrient-rich environment that promotes the growth of Candida and other fungal organisms that are normally present in low numbers

Rationale

The glucose-rich urine produced by sodium-glucose cotransporter-2 inhibition bathes the perineal and genital tissues as it passes through the urethra and exits the body. Glucose is an excellent carbon source for Candida species that normally reside in the genital area at low colonization levels. The elevated local glucose concentration from glycosuric urine promotes Candida overgrowth, producing vulvovaginal candidiasis in women and balanitis in men. This mechanism directly links the drug's therapeutic mechanism — glycosuria — to its most common adverse effect. Sodium-glucose cotransporter-2 inhibitors do not suppress genitourinary innate immunity, do not reduce secretory immunoglobulin A, and do not increase local blood flow through nitric oxide production as the basis for this adverse effect.

Correct Answer

A — Patients with established peripheral vascular disease or a prior lower extremity amputation

Rationale

The CANVAS trial identified an approximately twofold increased risk of lower extremity amputations with canagliflozin compared with placebo, predominantly at the level of the toe or metatarsal. The mechanism is not fully established but likely involves volume depletion-related reductions in peripheral perfusion in patients with already-compromised distal circulation. Patients with established peripheral vascular disease, prior amputation, neuropathy, or active foot ulcers are most vulnerable. In these patients, clinicians should either avoid canagliflozin in favor of empagliflozin or dapagliflozin (which carry no boxed warning for amputation), or proceed with close monitoring. Chronic kidney disease, heart failure, and prior mycotic infections do not specifically heighten the amputation risk from canagliflozin.

Correct Answer

C — Hold empagliflozin 3 to 4 days before surgery because the perioperative period — with reduced oral intake, surgical stress, and altered insulin dynamics — increases the risk of euglycemic diabetic ketoacidosis

Rationale

Sodium-glucose cotransporter-2 inhibitors should be held 3 to 4 days before elective surgery. The perioperative period creates conditions that dramatically increase the risk of euglycemic diabetic ketoacidosis: reduced carbohydrate intake lowers the glucose stimulus for insulin, surgical stress raises glucagon and counter-regulatory hormones, and the patient is often fasting. Sodium-glucose cotransporter-2 inhibitor-driven glycosuria continues to suppress insulin secretion while the glucagon-predominant hormonal environment promotes ketogenesis — the same mechanism as outpatient euglycemic diabetic ketoacidosis, but amplified by the perioperative state. Because blood glucose may remain near-normal, the ketoacidosis is easily missed. Holding the drug for 3 to 4 days allows the glycosuric effect to wane before surgery. Empagliflozin does not impair wound healing through diuresis, is not continued perioperatively, and does not accumulate in adipose tissue requiring a 7-day washout.

Correct Answer

B — Empagliflozin

Rationale

Empagliflozin is approved for heart failure with reduced ejection fraction based on the EMPEROR-Reduced trial, which demonstrated a 25 percent relative reduction in cardiovascular death or worsening heart failure in patients with ejection fraction below 40 percent — including those without diabetes. The mechanism is largely glucose-independent: osmotic diuresis and natriuresis reduce cardiac preload, complementing the furosemide already in this patient's regimen through a distinct tubular mechanism. Dapagliflozin would also be appropriate based on the Dapagliflozin and Prevention of Adverse Outcomes in Heart Failure trial. Pioglitazone is contraindicated in heart failure because it causes fluid retention through renal peroxisome proliferator-activated receptor gamma activation, worsening volume overload — the opposite of what is needed here. Sitagliptin has no proven heart failure benefit and saxagliptin actually increased heart failure hospitalizations in SAVOR-TIMI 53. Glipizide carries hypoglycemia risk and no cardiorenal benefit.

Correct Answer

D — Sodium-glucose cotransporter-2 inhibitors restore tubuloglomerular feedback by increasing macula densa sodium delivery, reducing glomerular hyperfiltration — a complementary mechanism to renin-angiotensin-aldosterone system blockade that together produce greater intraglomerular pressure reduction and renoprotection than either alone

Rationale

Renin-angiotensin-aldosterone system blockade reduces intraglomerular pressure primarily by dilating the efferent arteriole, reducing the pressure driving filtration. Sodium-glucose cotransporter-2 inhibitors reduce intraglomerular pressure by a complementary mechanism: restoring tubuloglomerular feedback through increased macula densa sodium delivery, which constricts the afferent arteriole and reduces the glomerular filtration rate from the upstream side. The combination of efferent dilation and afferent constriction produces greater intraglomerular pressure reduction than either mechanism alone — this complementarity is the pharmacological rationale for the combination. Trials such as CREDENCE (canagliflozin) and DAPA-CKD (dapagliflozin) confirmed 30 to 44 percent reductions in composite renal endpoints when sodium-glucose cotransporter-2 inhibitors were added to maximum renin-angiotensin-aldosterone system blockade. Sodium-glucose cotransporter-2 inhibitors do not block megalin-cubilin, do not inhibit tubular angiotensin-converting enzyme, and do not act through prostaglandin synthesis.

Correct Answer

A — Empagliflozin causes ongoing urinary glucose excretion that prevents blood glucose from rising despite active ketogenesis; the reduced glucose-stimulated insulin secretion from glycosuria and the glucagon-predominant state together drive ketone production at blood glucose levels that do not appear hyperglycemic

Rationale

This is euglycemic diabetic ketoacidosis — the presentation that the intern missed precisely because the blood glucose of 156 mg/dL is far below the levels seen in typical diabetic ketoacidosis. The mechanism is the key teaching point. Empagliflozin continuously excretes glucose in the urine, preventing blood glucose from rising even as gluconeogenesis and glycogenolysis attempt to maintain glucose levels. The ongoing glycosuria reduces the glucose stimulus for insulin secretion, producing a relative insulin deficiency. Combined with the glucagon-predominant state exacerbated by fasting and vomiting, hepatic ketogenesis is driven vigorously. Ketones accumulate and produce profound acidosis while blood glucose remains near-normal because the drug is literally excreting the glucose as fast as it is produced. This is why sodium-glucose cotransporter-2 inhibitors should be held before elective surgery, and why any patient on these agents with gastrointestinal illness should have ketones checked regardless of blood glucose. Vomiting produces metabolic alkalosis, which would partially offset rather than contribute to the acidosis, and cannot explain the degree of ketoacidosis seen here.

Correct Answer

C — Empagliflozin or dapagliflozin are appropriate choices; canagliflozin should be avoided because it carries an FDA boxed warning for lower extremity amputations, which is most relevant in patients with peripheral vascular disease or prior amputation

Rationale

The class is not contraindicated in patients with peripheral arterial disease or prior amputation — the cardiovascular outcome data support using sodium-glucose cotransporter-2 inhibitors in high-risk patients, and this patient would benefit. However, canagliflozin specifically carries an FDA boxed warning for lower extremity amputations based on the CANVAS trial signal, and the risk was concentrated in patients with established peripheral vascular disease, prior amputation, or neuropathy. In this patient — with peripheral arterial disease and a prior below-knee amputation — the appropriate response is to use a sodium-glucose cotransporter-2 inhibitor with proven cardiovascular benefit but without the amputation warning: empagliflozin (EMPA-REG OUTCOME) or dapagliflozin (DECLARE-TIMI 58). Canagliflozin's amputation signal has not been retracted. Ertugliflozin has no proven cardiovascular superiority and is not preferred for cardiovascular risk reduction.