Drug Classification · Questions 1–6
Identify the pharmacological class or categorical label for each drug or receptor. Vocabulary preparation is sufficient to answer every question in this section.
Question 1
Which of the following drugs is classified as a second-generation sulfonylurea?
Correct Answer
C — Glipizide
Rationale
Glipizide is a second-generation sulfonylurea, along with glyburide and glimepiride. Repaglinide is a meglitinide. Metformin is a biguanide. Chlorpropamide is a first-generation sulfonylurea that has largely been replaced by second-generation agents.
Question 2
Which of the following drugs is classified as a meglitinide?
Correct Answer
A — Repaglinide
Rationale
Repaglinide is a meglitinide, along with nateglinide. Meglitinides are rapid-onset, short-acting insulin secretagogues. Glipizide is a second-generation sulfonylurea. Metformin is a biguanide. Pioglitazone is a thiazolidinedione.
Question 3
Which of the following drugs is classified as a biguanide?
Correct Answer
D — Metformin
Rationale
Metformin is the only biguanide in current clinical use. Glimepiride is a second-generation sulfonylurea. Nateglinide is a meglitinide. Pioglitazone is a thiazolidinedione.
Question 4
Which of the following drugs is classified as a second-generation sulfonylurea that carries a specific warning for use in elderly patients due to its active metabolites?
Correct Answer
B — Glyburide
Rationale
Glyburide is a second-generation sulfonylurea listed on the Beers Criteria as a potentially inappropriate medication in elderly patients because of its active metabolites, which accumulate in renal impairment and cause prolonged hypoglycemia. Repaglinide and nateglinide are meglitinides. Metformin is a biguanide.
Question 5
Glimepiride belongs to which of the following pharmacological classes?
Correct Answer
A — Second-generation sulfonylurea
Rationale
Glimepiride is classified as a second-generation sulfonylurea, along with glipizide and glyburide. Meglitinides (repaglinide, nateglinide) are a distinct class of rapid-onset insulin secretagogues. Metformin is a biguanide. Acarbose and miglitol are alpha-glucosidase inhibitors.
Question 6
Nateglinide belongs to which of the following pharmacological classes?
Correct Answer
C — Meglitinide
Rationale
Nateglinide is classified as a meglitinide, along with repaglinide. Second-generation sulfonylureas include glipizide, glyburide, and glimepiride. Metformin is a biguanide. Acarbose and miglitol are alpha-glucosidase inhibitors.
Core Pharmacology · Questions 7–14
Apply your understanding of drug mechanisms, pharmacokinetics, and adverse effects. Each question requires one reasoning step.
Question 7
A patient with type 2 diabetes mellitus takes glipizide once daily. Despite not missing any meals, he experiences episodes of symptomatic hypoglycemia between meals. Which of the following best explains why sulfonylureas carry an intrinsic risk of hypoglycemia that is not shared by metformin?
Correct Answer
B — Sulfonylureas close adenosine triphosphate-sensitive potassium channels in beta cells regardless of the prevailing blood glucose level, stimulating insulin secretion even when glucose is already normal or low
Rationale
Sulfonylureas bind to the sulfonylurea receptor 1 subunit of the adenosine triphosphate-sensitive potassium channel in pancreatic beta cells, closing the channel and triggering the same downstream cascade as glucose — membrane depolarization, calcium influx, and insulin granule exocytosis. Because this closure occurs independent of blood glucose concentration, insulin is secreted even when glucose is already in the normal or low range, making hypoglycemia an intrinsic pharmacological consequence. Metformin suppresses hepatic glucose output without stimulating insulin secretion and therefore carries no intrinsic hypoglycemia risk as monotherapy.
Question 8
A patient with type 2 diabetes mellitus and an unpredictable work schedule often skips lunch on busy days. Her physician switches her from glipizide to repaglinide and instructs her to take it only when she eats a meal and skip the dose when she skips the meal. Which of the following best explains why this dosing strategy reduces between-meal hypoglycemia with repaglinide but would not be safe with glipizide?
Correct Answer
D — Repaglinide has a very short duration of action of 2 to 4 hours, so its insulin-stimulating effect is tightly coupled to the meal it is taken with, whereas glipizide's longer duration continues to drive insulin secretion between meals
Rationale
Meglitinides such as repaglinide are rapidly absorbed and short-acting, with a duration of 2 to 4 hours. When taken immediately before a meal, the insulin secretory effect peaks with the postprandial glucose rise and dissipates before the next meal, substantially reducing between-meal hypoglycemia. Glipizide, as a sulfonylurea, has a longer duration of action that persists between meals, continuing to drive insulin secretion even during fasting periods. Both agents share the same mechanism of closing adenosine triphosphate-sensitive potassium channels — the critical pharmacokinetic difference is duration, not receptor selectivity or glucose dependency.
Question 9
Metformin lowers blood glucose without stimulating insulin secretion. Which of the following best describes the molecular mechanism by which metformin reduces hepatic glucose output?
Correct Answer
A — Metformin inhibits mitochondrial complex I, reducing hepatic energy state and activating AMP-activated protein kinase, which suppresses gluconeogenic enzymes
Rationale
Metformin's primary molecular action is inhibition of mitochondrial complex I of the respiratory chain. This reduces the hepatic energy state and raises the ratio of AMP to adenosine triphosphate inside hepatocytes, activating AMP-activated protein kinase. Activated AMP-activated protein kinase phosphorylates and inactivates key gluconeogenic enzymes and transcription factors, suppressing glucose output from the liver. Metformin does not block glucagon receptors, activate insulin receptors directly, or inhibit glucose transporter 2.
Question 10
Among the second-generation sulfonylureas, glyburide is specifically avoided in patients with significant renal impairment. Which of the following best explains why glyburide poses a greater hypoglycemia risk in renal impairment than glipizide or glimepiride?
Correct Answer
C — Glyburide has pharmacologically active metabolites that are renally excreted and accumulate when kidney function is reduced, prolonging the insulin-stimulating effect
Rationale
Glyburide is metabolized to active metabolites that retain insulin-stimulating activity and are eliminated by the kidney. When renal function is impaired, these metabolites accumulate, extending the duration of beta cell stimulation and substantially increasing the risk of prolonged, severe hypoglycemia. Glipizide and glimepiride are metabolized to inactive or minimally active metabolites, making them safer alternatives in patients with renal impairment. Receptor binding potency differences and uremic protein displacement are not the relevant mechanism for glyburide's preferential risk.
Question 11
A patient with type 2 diabetes mellitus and stage 3b chronic kidney disease is admitted with nausea, myalgias, and an arterial blood gas showing a wide anion gap metabolic acidosis. His metformin was continued at full dose despite his declining renal function. Which of the following best explains the mechanism of this complication?
Correct Answer
B — Metformin accumulates in renal impairment and inhibits hepatic lactate metabolism, causing lactate to build up and produce a metabolic acidosis
Rationale
Metformin is excreted unchanged by the kidneys. When renal function is impaired, metformin accumulates in the body and inhibits hepatic lactate metabolism by suppressing mitochondrial complex I activity in hepatocytes. The liver normally clears lactate from the circulation; when this capacity is overwhelmed, lactate accumulates and produces a high anion gap metabolic acidosis. Metformin is contraindicated when estimated glomerular filtration rate falls below 30 mL/min for this reason. Metformin does not directly acidify blood as an ion, stimulate muscle anaerobic glycolysis constitutively, or inhibit tubular bicarbonate reabsorption.
Question 12
A patient with type 2 diabetes mellitus taking repaglinide is started on gemfibrozil for hypertriglyceridemia. Shortly afterward he develops recurrent hypoglycemia. Which of the following best explains the mechanism of this drug interaction?
Correct Answer
D — Gemfibrozil inhibits cytochrome P450 2C8, a key metabolic pathway for repaglinide, causing repaglinide levels to rise markedly
Rationale
Repaglinide is a substrate of both cytochrome P450 3A4 and cytochrome P450 2C8. Gemfibrozil is a potent inhibitor of cytochrome P450 2C8, and this inhibition markedly elevates repaglinide plasma levels, prolonging and intensifying its insulin-stimulating effect and producing hypoglycemia. This interaction is clinically significant and the combination is generally avoided. Gemfibrozil does not displace repaglinide from protein binding, stimulate the sulfonylurea receptor 1, or substantially inhibit cytochrome P450 3A4 at therapeutic doses.
Question 13
A patient who has been taking metformin for eight years develops paresthesias in his feet. Laboratory work shows a low serum vitamin B12 level. Which of the following best explains how long-term metformin use leads to vitamin B12 deficiency?
Correct Answer
A — Metformin interferes with calcium-dependent binding of the intrinsic factor–vitamin B12 complex to its ileal receptor, reducing absorption
Rationale
Long-term metformin use reduces vitamin B12 absorption through interference with the calcium-dependent attachment of the intrinsic factor–vitamin B12 complex to its receptor on ileal enterocytes. This mechanism is distinct from pernicious anemia, in which intrinsic factor itself is absent. Calcium supplementation has been shown to partially reverse this effect. Metformin does not inhibit gastric acid secretion, suppress ileal transport protein expression via AMP-activated protein kinase, or increase renal vitamin B12 clearance.
Question 14
A physician considers prescribing glimepiride for a newly diagnosed patient who turns out to have type 1 diabetes mellitus rather than type 2 diabetes mellitus. Which of the following best explains why sulfonylureas are ineffective in type 1 diabetes mellitus?
Correct Answer
C — Sulfonylureas work by closing adenosine triphosphate-sensitive potassium channels on pancreatic beta cells to stimulate insulin release, but type 1 diabetes mellitus involves destruction of beta cells, leaving no functional target for the drug
Rationale
Sulfonylureas depend entirely on functional pancreatic beta cells to produce their glucose-lowering effect — they stimulate insulin release from beta cells by closing adenosine triphosphate-sensitive potassium channels. In type 1 diabetes mellitus, autoimmune destruction of beta cells eliminates the cellular target. There is no beta cell function remaining for the drug to act upon. Type 1 diabetes mellitus does not involve peripheral insulin receptor resistance as its primary defect, and autoantibodies do not inactivate the sulfonylurea receptor or degrade the drug systemically.
Clinical Correlations · Questions 15–18
Apply pharmacological knowledge to clinical scenarios. Each vignette presents a patient situation; the question tests mechanism of action or drug selection.
Question 15
A 62-year-old man with type 2 diabetes mellitus has been well controlled on metformin 1000 mg twice daily for three years with no episodes of hypoglycemia. His hemoglobin A1c remains at 7.8 percent, so glipizide 5 mg daily is added. Six weeks later he presents with episodes of confusion and diaphoresis occurring between meals. His blood glucose during one episode is 51 mg/dL. Which of the following best explains why adding glipizide introduced a hypoglycemia risk that metformin alone did not produce?
Correct Answer
B — Glipizide stimulates insulin secretion by closing adenosine triphosphate-sensitive potassium channels on beta cells regardless of blood glucose level, whereas metformin suppresses hepatic glucose output without stimulating insulin secretion
Rationale
Metformin lowers blood glucose by suppressing hepatic gluconeogenesis through inhibition of mitochondrial complex I and activation of adenosine monophosphate-activated protein kinase. Because it does not stimulate insulin secretion, it carries no intrinsic hypoglycemia risk as monotherapy — three years without episodes confirms this in the patient. Glipizide closes adenosine triphosphate-sensitive potassium channels on pancreatic beta cells independent of the prevailing blood glucose concentration, triggering insulin secretion even when glucose is already normal or falling. This glucose-independent insulin drive is the mechanistic basis for hypoglycemia risk with all sulfonylureas. The patient's clinical history — no hypoglycemia on metformin alone, episodes beginning only after glipizide was added — directly implicates the new agent and its mechanism.
Question 16
A 78-year-old man with type 2 diabetes mellitus and an estimated glomerular filtration rate of 28 mL/min has been taking glyburide for several years. He is brought to the emergency department with confusion and a blood glucose of 34 mg/dL. Intravenous dextrose is administered, but hypoglycemia recurs three times over the next 12 hours despite repeated glucose infusions. Which of the following best explains why his hypoglycemia is so prolonged?
Correct Answer
D — Glyburide produces active metabolites that accumulate when renal excretion is impaired, prolonging beta cell stimulation and insulin secretion well beyond the expected drug duration
Rationale
Glyburide is metabolized to pharmacologically active metabolites that are normally eliminated by the kidney. When renal function is severely impaired — as in this patient with an estimated glomerular filtration rate of 28 mL/min — these active metabolites cannot be cleared and accumulate, continuously stimulating adenosine triphosphate-sensitive potassium channel closure in beta cells and driving ongoing insulin secretion for hours after the last dose. This explains why repeated glucose administration cannot fully restore euglycemia: the insulin-stimulating driver persists as long as the metabolites remain in circulation. Glyburide is listed on the Beers Criteria as a potentially inappropriate medication in elderly patients for this reason, and current guidelines recommend avoiding it when estimated glomerular filtration rate falls below 60 mL/min.
Question 17
A 61-year-old woman with type 2 diabetes mellitus and mild chronic kidney disease (estimated glomerular filtration rate 38 mL/min) takes metformin 1000 mg twice daily. She undergoes a computed tomography scan with intravenous contrast for evaluation of a lung nodule. Two days later she develops weakness, nausea, and abdominal pain. Laboratory evaluation shows a serum lactate of 8.4 mmol/L and a high anion gap metabolic acidosis. Which of the following best explains the mechanism of this complication?
Correct Answer
A — Contrast-induced nephropathy worsened her renal function, reducing metformin clearance, causing metformin to accumulate and inhibit hepatic lactate metabolism
Rationale
Metformin is excreted unchanged by the kidneys. This patient's baseline renal function was already reduced (estimated glomerular filtration rate 38 mL/min), placing her at the threshold for caution. Iodinated contrast caused additional nephrotoxic injury, acutely worsening her renal function and reducing metformin clearance. As metformin accumulated, it inhibited mitochondrial complex I activity in hepatocytes, impairing the liver's ability to metabolize lactate from the circulation. Lactate accumulation produced the high anion gap metabolic acidosis. Metformin does not react chemically with contrast media, is minimally protein-bound (making displacement pharmacologically irrelevant), and does not interfere with tubular contrast excretion.
Question 18
A 51-year-old woman with type 2 diabetes mellitus has been stable on repaglinide taken with each meal for eight months without hypoglycemic episodes. She develops a vaginal candida infection and is prescribed fluconazole for seven days. On day three of fluconazole treatment she experiences sweating, palpitations, and a blood glucose of 44 mg/dL two hours after lunch. Which of the following best explains the mechanism of this new hypoglycemic episode?
Correct Answer
C — Fluconazole inhibits cytochrome P450 3A4, one of the enzymes responsible for repaglinide metabolism, causing repaglinide plasma levels to rise and its insulin-stimulating effect to intensify
Rationale
Repaglinide is metabolized by both cytochrome P450 2C8 and cytochrome P450 3A4. Fluconazole is a potent inhibitor of cytochrome P450 3A4 (and to a lesser degree cytochrome P450 2C8). When fluconazole is added, repaglinide clearance is reduced, plasma concentrations rise, and the duration and magnitude of its adenosine triphosphate-sensitive potassium channel-closing effect on beta cells are amplified — producing hypoglycemia at a previously well-tolerated dose. The eight months of stability before fluconazole was added, and the onset of hypoglycemia on day three of the new drug, make the pharmacokinetic interaction the most clinically consistent explanation. Fluconazole has no direct action at the insulin-secreting machinery or at the sulfonylurea receptor, and protein binding displacement is not the mechanism of this interaction.