Pharmacology Quiz: Metformin
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MetforminQuestion 1 of 20

The standard clinical practice of initiating metformin at a low dose (e.g., 500 mg daily) and slowly titrating upwards over several weeks is primarily designed to improve patient tolerance by minimizing:

The risk of developing vitamin B12 deficiency over the long term.
The slight but measurable increase in serum lactate levels.
The potential for acute kidney injury during initiation.
The severity of initial gastrointestinal adverse effects.
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Pharmacology Quiz

Pharmacology Quiz: Metformin

Practice Metformin in Pharmacology with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Metformin, giving you a quick way to practice the rules, question types, and explanations that matter most for Pharmacology.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

The standard clinical practice of initiating metformin at a low dose (e.g., 500 mg daily) and slowly titrating upwards over several weeks is primarily designed to improve patient tolerance by minimizing:

  1. The risk of developing vitamin B12 deficiency over the long term.
  2. The slight but measurable increase in serum lactate levels.
  3. The potential for acute kidney injury during initiation.
  4. The severity of initial gastrointestinal adverse effects. (correct answer)
Explanation: When you encounter questions about drug dosing strategies, think about the primary clinical reason behind the specific approach. Metformin's "start low and go slow" protocol directly addresses its most common and immediate side effects. Metformin causes gastrointestinal upset in approximately 20-30% of patients, particularly during initial treatment. These effects include nausea, diarrhea, abdominal discomfort, and metallic taste. By starting at 500 mg daily and gradually increasing the dose over 2-4 weeks, you allow the GI tract to adapt, significantly reducing the severity and duration of these symptoms. This approach improves medication adherence and prevents patients from discontinuing therapy due to intolerable side effects. Looking at the incorrect options: Choice A is wrong because vitamin B12 deficiency develops over months to years of metformin use, not during initiation, so slow titration doesn't prevent this long-term effect. Choice B misunderstands metformin's mechanism—while metformin can slightly increase lactate levels, this isn't the reason for gradual dosing, and the increase is generally clinically insignificant in patients with normal kidney function. Choice C incorrectly suggests acute kidney injury is a primary concern during initiation; metformin is actually contraindicated in patients with existing kidney dysfunction, and gradual dosing doesn't prevent kidney injury. Remember this pattern: when you see questions about drug titration strategies, the most immediate and common side effects usually drive the dosing approach. For metformin, GI tolerance is the limiting factor that determines how quickly you can reach therapeutic doses.

Question 2

A 68-year-old male with type 2 diabetes, managed with metformin 1000 mg twice daily, presents for a routine follow-up. His laboratory results show a serum creatinine of 1.7 mg/dL and an estimated glomerular filtration rate (eGFR) of 35 mL/min/1.73 m². He is otherwise asymptomatic with an HbA1c of 7.1%. Which of the following is the most appropriate management plan regarding his metformin therapy?

  1. Discontinue metformin immediately due to the high risk of fatal lactic acidosis.
  2. Reduce the metformin dose to 500 mg daily and monitor renal function more frequently. (correct answer)
  3. Continue the current metformin dose but advise the patient to increase fluid intake.
  4. Switch metformin to glyburide to achieve better glycemic control with impaired renal function.
Explanation: Current guidelines recommend against initiating metformin if the eGFR is <45 mL/min/1.73 m², but for patients already on metformin whose eGFR falls between 30-45, the recommendation is to assess risks and benefits, consider a dose reduction (e.g., by 50%), and monitor renal function more frequently (e.g., every 3 months). Discontinuing immediately (A) is typically reserved for eGFR <30. Continuing the full dose (C) is inappropriate as it increases the risk of drug accumulation and lactic acidosis. Switching to glyburide (D), a long-acting sulfonylurea, is a poor choice in renal impairment due to the high risk of prolonged hypoglycemia.

Question 3

The primary antihyperglycemic effect of metformin is the suppression of hepatic gluconeogenesis. This is initiated by metformin's inhibition of mitochondrial respiratory chain complex I, which leads most directly to:

  1. A decrease in the cellular AMP:ATP ratio, deactivating AMPK.
  2. An increase in the cellular AMP:ATP ratio, activating AMPK. (correct answer)
  3. A decrease in the cellular NADH:NAD+ ratio, promoting fatty acid oxidation.
  4. An increase in the cellular NADH:NAD+ ratio, inhibiting glycolysis.
Explanation: Metformin's inhibition of mitochondrial complex I impairs ATP synthesis, causing cellular energy stress. This leads to an accumulation of AMP relative to ATP, thus increasing the AMP:ATP ratio. This increased ratio is the key signal that allosterically activates AMP-activated protein kinase (AMPK). Activated AMPK then phosphorylates downstream targets that suppress the transcription of gluconeogenic enzymes. A decrease in the ratio (A) would be incorrect. Inhibition of complex I would lead to an accumulation of NADH, thus increasing (not decreasing) the NADH:NAD+ ratio (C, D).

Question 4

Unlike sulfonylureas, metformin is considered a 'euglycemic' agent because it lowers elevated blood glucose without causing hypoglycemia in monotherapy. This is because metformin's mechanism of action primarily involves:

  1. Stimulating pancreatic beta-cells to release pre-formed insulin.
  2. Blocking the reabsorption of glucose in the proximal renal tubule.
  3. Reducing hepatic glucose production and improving peripheral insulin sensitivity. (correct answer)
  4. Slowing gastric emptying and inhibiting the action of glucagon.
Explanation: Metformin's primary mechanism is reducing hepatic glucose output and increasing insulin-mediated peripheral glucose uptake. It does not actively drive blood glucose down by stimulating insulin secretion, which is the mechanism of sulfonylureas (A) and the reason they can cause hypoglycemia. Metformin's actions are glucose-dependent and do not function in a way that would cause hypoglycemia on their own. (B) describes SGLT2 inhibitors. (D) describes actions more characteristic of GLP-1 receptor agonists.

Question 5

A 62-year-old patient on metformin and ramipril is hospitalized for an acute myocardial infarction complicated by cardiogenic shock. His metformin is held upon admission. What is the most compelling physiological reason for this action, even if his admission creatinine is normal?

  1. An acute MI increases the risk of metformin-induced gastrointestinal bleeding.
  2. Cardiogenic shock causes profound tissue hypoxia, increasing lactate production. (correct answer)
  3. Beta-blockers used post-MI can mask the symptoms of metformin-induced hypoglycemia.
  4. Ramipril and metformin have a synergistic effect that can cause severe hyperkalemia in this setting.
Explanation: Cardiogenic shock is a state of severe systemic hypoperfusion and tissue hypoxia. Hypoxia forces cells to rely on anaerobic metabolism, which generates large amounts of lactate. This acute increase in lactate production, combined with impaired lactate clearance due to poor liver and kidney perfusion, creates a high-risk environment for the development of metformin-associated lactic acidosis. This risk exists even with normal baseline renal function. Metformin does not increase bleeding risk (A), does not cause hypoglycemia (C), and does not have a clinically significant interaction with ramipril causing hyperkalemia (D).

Question 6

A pharmacist is counseling a patient about a new prescription for metformin extended-release (ER). Which instruction is essential for the patient to understand regarding the administration of this specific formulation?

  1. It is normal to see a tablet-like object, or 'ghost pill,' in your stool. (correct answer)
  2. Crush the tablet and mix with applesauce if you have difficulty swallowing it whole.
  3. Take this medication 30 minutes before your first meal of the day for best effect.
  4. Split the tablets in half if you experience stomach upset to take a smaller dose.
Explanation: When counseling patients about extended-release formulations, you need to understand how these drug delivery systems work and what patients should expect during treatment. Metformin ER uses a special tablet matrix that controls drug release over time. As the tablet moves through your digestive system, the active drug is gradually released while the inert tablet shell remains largely intact. This means you'll often see what looks like a whole tablet in your stool - this is completely normal and called a "ghost pill." The medication has been properly absorbed; you're just seeing the empty shell. Answer A correctly identifies this essential counseling point that prevents patient anxiety and medication discontinuation. Answer B is dangerous because crushing ER tablets destroys the controlled-release mechanism, potentially causing dose dumping and increased side effects. Answer C is incorrect - while metformin should be taken with food to reduce GI upset, the "30 minutes before meals" instruction is more relevant for immediate-release formulations and certain other diabetes medications. Answer D is also unsafe because splitting ER tablets can compromise the release mechanism and lead to unpredictable drug absorption. Remember that extended-release formulations require special counseling about their unique characteristics. Always emphasize that patients should never crush, chew, or split these tablets unless specifically indicated by the manufacturer. The ghost pill phenomenon is particularly important to discuss proactively - many patients panic when they see intact tablets in their stool and stop taking essential medications.

Question 7

Metformin's therapeutic action in type 2 diabetes involves improving insulin sensitivity in peripheral tissues. This effect is primarily mediated by the activation of AMPK, which in turn leads to:

  1. Enhanced translocation of GLUT4 glucose transporters to the cell membrane. (correct answer)
  2. Increased transcription of the insulin receptor gene.
  3. Direct inhibition of protein tyrosine phosphatase 1B (PTP1B).
  4. Stimulation of insulin secretion from pancreatic beta-cells.
Explanation: When you encounter questions about metformin's mechanism of action, focus on its role as an AMPK activator and how this affects glucose metabolism at the cellular level. Metformin activates AMPK (AMP-activated protein kinase), which acts as the cell's energy sensor. When AMPK is activated, it triggers a cascade that ultimately enhances glucose uptake by promoting the translocation of GLUT4 transporters from intracellular vesicles to the cell membrane. This increased presence of glucose transporters on the cell surface allows more glucose to enter muscle and adipose tissue, improving insulin sensitivity. This makes option A correct. Let's examine why the other options are incorrect: Option B suggests increased insulin receptor transcription, but AMPK activation primarily affects post-translational processes like GLUT4 translocation rather than gene transcription of insulin receptors. Option C mentions direct PTP1B inhibition, but while metformin may indirectly affect PTP1B activity, its primary mechanism through AMPK doesn't directly inhibit this phosphatase. Option D describes stimulation of insulin secretion, which is actually the mechanism of sulfonylureas, not metformin. Metformin is specifically an insulin sensitizer, not an insulin secretagogue. For pharmacology exams, remember that metformin is fundamentally different from other diabetes medications because it doesn't increase insulin production. Instead, it makes existing insulin work better by enhancing glucose uptake in peripheral tissues through the AMPK-GLUT4 pathway. This distinction helps you quickly eliminate options related to insulin secretion or receptor synthesis.

Question 8

A 58-year-old female with type 2 diabetes is scheduled for a coronary angiogram with an iodinated contrast agent. Her current medications include metformin, lisinopril, and atorvastatin. Her eGFR is 52 mL/min/1.73 m². What is the most appropriate instruction regarding her metformin therapy?

  1. Continue metformin without interruption as her renal function is stable.
  2. Withhold metformin on the day of the procedure and for 48 hours after. (correct answer)
  3. Permanently discontinue metformin and switch to an alternative agent.
  4. Decrease the metformin dose by half for one week before and after the procedure.
Explanation: Guidelines recommend temporarily withholding metformin before and after administration of iodinated contrast media in patients with an eGFR between 30 and 60 mL/min/1.73 m². This is a precaution against contrast-induced nephropathy, which could cause metformin to accumulate and precipitate lactic acidosis. The standard procedure is to hold the drug on the day of and for 48 hours after the procedure, rechecking renal function before resuming. Continuing metformin (A) is not recommended. Permanent discontinuation (C) is unnecessary. A one-week dose reduction (D) is not the standard protocol.

Question 9

A patient with newly diagnosed type 2 diabetes is started on immediate-release metformin, titrating up to 1000 mg twice daily. The patient calls the clinic complaining of persistent, bothersome diarrhea. Which is the most appropriate next step to manage this adverse effect?

  1. Advise the patient to take the medication on an empty stomach to increase absorption.
  2. Add loperamide to the patient's regimen to be taken with each dose of metformin.
  3. Discontinue metformin and initiate therapy with an SGLT2 inhibitor.
  4. Switch to an equivalent total daily dose of an extended-release (ER) metformin formulation. (correct answer)
Explanation: Gastrointestinal side effects are the most common adverse effect of metformin. Switching from the immediate-release to an extended-release formulation often significantly improves GI tolerability due to a slower rate of drug absorption. Taking metformin with food, not on an empty stomach (A), is recommended to reduce side effects. While loperamide (B) can manage symptoms, it does not address the underlying cause of intolerance. Discontinuing a first-line agent (C) is not necessary until more conservative measures, like switching formulations, have been tried.

Question 10

A patient with type 2 diabetes and a history of alcohol use disorder is advised to avoid binge drinking while taking metformin. This is because acute alcohol intoxication can increase the risk of metformin-associated lactic acidosis by which two primary mechanisms?

  1. Increasing metformin absorption and decreasing its protein binding.
  2. Inhibiting hepatic gluconeogenesis and altering the intracellular redox state. (correct answer)
  3. Causing direct pancreatic toxicity and inducing a state of insulin resistance.
  4. Inducing CYP450 enzymes and accelerating the formation of a toxic metabolite.
Explanation: Acute alcohol consumption exacerbates the risk of lactic acidosis with metformin in two main ways. First, alcohol metabolism in the liver increases the NADH/NAD+ ratio. This altered redox state inhibits the conversion of lactate to pyruvate, thus impairing lactate clearance. Second, this same redox shift inhibits gluconeogenesis (of which lactate is a substrate), which can lead to hypoglycemia and further stress metabolism. Alcohol does not affect metformin's absorption or binding (A), nor does it produce a toxic metabolite via CYP induction (D).

Question 11

A patient with type 2 diabetes has been taking metformin for six years. She presents with new-onset symmetric, stocking-glove paresthesia and is found to have a megaloblastic anemia on a complete blood count. These findings are most likely due to which metformin-induced mechanism?

  1. Direct neurotoxic accumulation of metformin in peripheral nerve sheaths.
  2. Inhibition of intrinsic factor secretion, leading to pernicious anemia.
  3. Impaired calcium-dependent absorption of vitamin B12 in the terminal ileum. (correct answer)
  4. Chronic, subclinical lactic acidosis causing progressive axonal damage.
Explanation: Long-term metformin use is a known cause of vitamin B12 deficiency. The mechanism is believed to be interference with the calcium-dependent binding of the vitamin B12-intrinsic factor complex to its receptor in the terminal ileum. Vitamin B12 is essential for myelin synthesis and erythropoiesis, and its deficiency can cause both peripheral neuropathy and megaloblastic anemia, mimicking diabetic neuropathy. Metformin is not directly neurotoxic (A), does not affect intrinsic factor secretion (B), and its risk is acute lactic acidosis, not a chronic subclinical state causing neuropathy (D).

Question 12

A 72-year-old man with type 2 diabetes on metformin is brought to the emergency department with sepsis from a urinary tract infection. He is hypotensive and confused. His arterial blood gas shows pH 7.15, PaCO2 25 mmHg, and HCO3- 10 mEq/L. This acid-base disturbance significantly increases his risk of metformin-associated lactic acidosis primarily because the underlying physiological state involves:

  1. Sepsis-induced acute kidney injury, leading to rapid metformin accumulation.
  2. Systemic tissue hypoperfusion, promoting anaerobic glycolysis and lactate production. (correct answer)
  3. Dehydration from fever and poor intake, leading to hemoconcentration of metformin.
  4. Direct inhibition of hepatic lactate clearance by circulating inflammatory cytokines.
Explanation: The patient's ABG shows a metabolic acidosis with respiratory compensation, characteristic of lactic acidosis, likely secondary to septic shock. The primary driver of this process is systemic tissue hypoperfusion (shock), which forces cells into anaerobic glycolysis. This dramatically increases lactate production. While metformin accumulation due to acute kidney injury (A) is a major contributing factor, the massive overproduction of lactate from hypoxia is the more direct and immediate threat that metformin exacerbates by inhibiting hepatic lactate clearance.

Question 13

A researcher develops a new biguanide that successfully activates AMPK but, unlike metformin, does not inhibit mitochondrial complex I. Which of metformin's characteristic effects would most likely be diminished or absent with this new compound?

  1. Increased glucose uptake in skeletal muscle.
  2. Decreased intestinal absorption of glucose.
  3. Reduction in plasma free fatty acid levels.
  4. Suppression of hepatic gluconeogenesis. (correct answer)
Explanation: When you encounter questions about metformin's mechanisms, remember that this drug works through two distinct pathways: AMPK activation (which drives most metabolic benefits) and mitochondrial complex I inhibition (which has more specific effects on hepatic metabolism). The key insight here is understanding what happens when you remove complex I inhibition while keeping AMPK activation intact. Metformin's inhibition of mitochondrial complex I specifically disrupts cellular respiration in hepatocytes, reducing ATP production and increasing the AMP/ATP ratio. This metabolic stress directly impairs gluconeogenesis because this pathway requires substantial ATP to convert substrates like lactate and amino acids into glucose. Without complex I inhibition, hepatocytes maintain normal ATP levels, allowing gluconeogenesis to proceed despite AMPK activation. Looking at the incorrect options: Choice A is wrong because increased skeletal muscle glucose uptake results from AMPK activation, which this new compound retains. Choice B is incorrect since decreased intestinal glucose absorption is mediated through AMPK-dependent mechanisms in enterocytes, not complex I inhibition. Choice C is wrong because reduced plasma free fatty acids occur through AMPK's effects on adipose tissue lipolysis and hepatic fatty acid oxidation. The correct answer is D because suppression of hepatic gluconeogenesis specifically requires the metabolic stress created by complex I inhibition, not just AMPK activation. Study tip: For biguanide questions, always distinguish between AMPK-mediated effects (peripheral glucose uptake, fatty acid metabolism) and complex I inhibition effects (primarily hepatic gluconeogenesis suppression). This distinction frequently appears on pharmacology exams.

Question 14

The standard clinical practice of initiating metformin at a low dose (e.g., 500 mg daily) and slowly titrating upwards over several weeks is primarily designed to improve patient tolerance by minimizing:

  1. The risk of developing vitamin B12 deficiency over the long term.
  2. The slight but measurable increase in serum lactate levels.
  3. The potential for acute kidney injury during initiation.
  4. The severity of initial gastrointestinal adverse effects. (correct answer)
Explanation: When you encounter questions about drug dosing strategies, think about the primary clinical reason behind the specific approach. Metformin's "start low and go slow" protocol directly addresses its most common and immediate side effects. Metformin causes gastrointestinal upset in approximately 20-30% of patients, particularly during initial treatment. These effects include nausea, diarrhea, abdominal discomfort, and metallic taste. By starting at 500 mg daily and gradually increasing the dose over 2-4 weeks, you allow the GI tract to adapt, significantly reducing the severity and duration of these symptoms. This approach improves medication adherence and prevents patients from discontinuing therapy due to intolerable side effects. Looking at the incorrect options: Choice A is wrong because vitamin B12 deficiency develops over months to years of metformin use, not during initiation, so slow titration doesn't prevent this long-term effect. Choice B misunderstands metformin's mechanism—while metformin can slightly increase lactate levels, this isn't the reason for gradual dosing, and the increase is generally clinically insignificant in patients with normal kidney function. Choice C incorrectly suggests acute kidney injury is a primary concern during initiation; metformin is actually contraindicated in patients with existing kidney dysfunction, and gradual dosing doesn't prevent kidney injury. Remember this pattern: when you see questions about drug titration strategies, the most immediate and common side effects usually drive the dosing approach. For metformin, GI tolerance is the limiting factor that determines how quickly you can reach therapeutic doses.

Question 15

Unlike sulfonylureas, metformin is considered a 'euglycemic' agent because it lowers elevated blood glucose without causing hypoglycemia in monotherapy. This is because metformin's mechanism of action primarily involves:

  1. Stimulating pancreatic beta-cells to release pre-formed insulin.
  2. Blocking the reabsorption of glucose in the proximal renal tubule.
  3. Reducing hepatic glucose production and improving peripheral insulin sensitivity. (correct answer)
  4. Slowing gastric emptying and inhibiting the action of glucagon.
Explanation: Metformin's primary mechanism is reducing hepatic glucose output and increasing insulin-mediated peripheral glucose uptake. It does not actively drive blood glucose down by stimulating insulin secretion, which is the mechanism of sulfonylureas (A) and the reason they can cause hypoglycemia. Metformin's actions are glucose-dependent and do not function in a way that would cause hypoglycemia on their own. (B) describes SGLT2 inhibitors. (D) describes actions more characteristic of GLP-1 receptor agonists.

Question 16

A clinician selects metformin for a patient with type 2 diabetes and obesity, citing its tendency to be weight-neutral or cause modest weight loss. This favorable effect on body weight is best explained by metformin's ability to:

  1. Lower blood glucose levels without causing a compensatory increase in insulin secretion. (correct answer)
  2. Significantly increase the basal metabolic rate through uncoupling of oxidative phosphorylation.
  3. Induce malabsorption of dietary fats and carbohydrates in the small intestine.
  4. Directly stimulate beta-oxidation of fatty acids within adipocytes.
Explanation: Many glucose-lowering therapies, such as insulin and sulfonylureas, cause weight gain because they increase circulating insulin levels. Insulin is an anabolic hormone that promotes energy storage. Metformin works by increasing insulin sensitivity and decreasing hepatic glucose output, which lowers glucose without stimulating endogenous insulin secretion. This avoidance of hyperinsulinemia is the primary reason for its favorable weight profile. It does not have a major effect on metabolic rate (B), cause significant malabsorption (C), or directly stimulate lipolysis in fat cells (D).

Question 17

The activation of AMP-activated protein kinase (AMPK) by metformin leads to the suppression of genes involved in hepatic gluconeogenesis, such as G6PC and PCK1. This transcriptional repression is mediated by AMPK through which downstream action?

  1. Directly binding to the promoter regions of gluconeogenic genes.
  2. Phosphorylating and activating the transcription factor ChREBP.
  3. Inhibiting the translocation of the transcription coactivator CRTC2 to the nucleus. (correct answer)
  4. Increasing the synthesis of cyclic AMP (cAMP) to antagonize glucagon signaling.
Explanation: A key mechanism for AMPK's suppression of gluconeogenesis is the phosphorylation of the CREB-regulated transcription coactivator 2 (CRTC2). This phosphorylation traps CRTC2 in the cytoplasm, preventing it from entering the nucleus and co-activating transcription factors like CREB, which are necessary to turn on gluconeogenic genes. AMPK does not directly bind DNA (A). It inhibits, rather than activates, ChREBP (B), which is involved in lipogenesis. It decreases, rather than increases, cAMP levels (D).

Question 18

A 68-year-old male with type 2 diabetes, managed with metformin 1000 mg twice daily, presents for a routine follow-up. His laboratory results show a serum creatinine of 1.7 mg/dL and an estimated glomerular filtration rate (eGFR) of 35 mL/min/1.73 m². He is otherwise asymptomatic with an HbA1c of 7.1%. Which of the following is the most appropriate management plan regarding his metformin therapy?

  1. Discontinue metformin immediately due to the high risk of fatal lactic acidosis.
  2. Reduce the metformin dose to 500 mg daily and monitor renal function more frequently. (correct answer)
  3. Continue the current metformin dose but advise the patient to increase fluid intake.
  4. Switch metformin to glyburide to achieve better glycemic control with impaired renal function.
Explanation: Current guidelines recommend against initiating metformin if the eGFR is <45 mL/min/1.73 m², but for patients already on metformin whose eGFR falls between 30-45, the recommendation is to assess risks and benefits, consider a dose reduction (e.g., by 50%), and monitor renal function more frequently (e.g., every 3 months). Discontinuing immediately (A) is typically reserved for eGFR <30. Continuing the full dose (C) is inappropriate as it increases the risk of drug accumulation and lactic acidosis. Switching to glyburide (D), a long-acting sulfonylurea, is a poor choice in renal impairment due to the high risk of prolonged hypoglycemia.

Question 19

A 72-year-old man with type 2 diabetes on metformin is brought to the emergency department with sepsis from a urinary tract infection. He is hypotensive and confused. His arterial blood gas shows pH 7.15, PaCO2 25 mmHg, and HCO3- 10 mEq/L. This acid-base disturbance significantly increases his risk of metformin-associated lactic acidosis primarily because the underlying physiological state involves:

  1. Sepsis-induced acute kidney injury, leading to rapid metformin accumulation.
  2. Systemic tissue hypoperfusion, promoting anaerobic glycolysis and lactate production. (correct answer)
  3. Dehydration from fever and poor intake, leading to hemoconcentration of metformin.
  4. Direct inhibition of hepatic lactate clearance by circulating inflammatory cytokines.
Explanation: The patient's ABG shows a metabolic acidosis with respiratory compensation, characteristic of lactic acidosis, likely secondary to septic shock. The primary driver of this process is systemic tissue hypoperfusion (shock), which forces cells into anaerobic glycolysis. This dramatically increases lactate production. While metformin accumulation due to acute kidney injury (A) is a major contributing factor, the massive overproduction of lactate from hypoxia is the more direct and immediate threat that metformin exacerbates by inhibiting hepatic lactate clearance.

Question 20

The primary antihyperglycemic effect of metformin is the suppression of hepatic gluconeogenesis. This is initiated by metformin's inhibition of mitochondrial respiratory chain complex I, which leads most directly to:

  1. A decrease in the cellular AMP:ATP ratio, deactivating AMPK.
  2. An increase in the cellular AMP:ATP ratio, activating AMPK. (correct answer)
  3. A decrease in the cellular NADH:NAD+ ratio, promoting fatty acid oxidation.
  4. An increase in the cellular NADH:NAD+ ratio, inhibiting glycolysis.
Explanation: Metformin's inhibition of mitochondrial complex I impairs ATP synthesis, causing cellular energy stress. This leads to an accumulation of AMP relative to ATP, thus increasing the AMP:ATP ratio. This increased ratio is the key signal that allosterically activates AMP-activated protein kinase (AMPK). Activated AMPK then phosphorylates downstream targets that suppress the transcription of gluconeogenic enzymes. A decrease in the ratio (A) would be incorrect. Inhibition of complex I would lead to an accumulation of NADH, thus increasing (not decreasing) the NADH:NAD+ ratio (C, D).