MTM Pharmacotherapy Review & Drug Interactions 3 — Questions and Answers
Question 1: A patient with chronic kidney disease (eGFR 20 mL/min) is taking gabapentin. What dose adjustment is required?
- No adjustment needed; gabapentin is hepatically metabolized
- Reduce dose and/or frequency; gabapentin is renally eliminated (Correct answer)
- Increase the dose to overcome reduced absorption
- Switch to pregabalin, which is unaffected by renal function
Correct answer: Reduce dose and/or frequency; gabapentin is renally eliminated
Gabapentin is exclusively renally eliminated without hepatic metabolism, requiring significant dose reduction in renal impairment to prevent neurotoxicity.
Question 2: Which drug interaction mechanism explains the reduced effectiveness of oral contraceptives when rifampin is co-administered?
- Rifampin inhibits CYP3A4, increasing estrogen levels
- Rifampin induces CYP3A4, accelerating estrogen metabolism (Correct answer)
- Rifampin chelates oral contraceptives in the GI tract
- Rifampin displaces estrogen from albumin binding sites
Correct answer: Rifampin induces CYP3A4, accelerating estrogen metabolism
Rifampin is a potent CYP3A4 inducer that significantly increases the metabolism of ethinyl estradiol and progestin components of oral contraceptives, reducing their plasma concentrations.
Question 3: In an MTM session, a patient on digoxin reports starting clarithromycin for a respiratory infection. What is the interaction mechanism?
- Clarithromycin induces P-glycoprotein, reducing digoxin absorption
- Clarithromycin inhibits P-glycoprotein and CYP3A4, increasing digoxin levels (Correct answer)
- Clarithromycin competes with digoxin for renal tubular secretion
- Clarithromycin displaces digoxin from tissue-binding sites
Correct answer: Clarithromycin inhibits P-glycoprotein and CYP3A4, increasing digoxin levels
Clarithromycin inhibits P-glycoprotein (which normally effluxes digoxin from intestinal cells and renal tubules), leading to increased digoxin absorption and decreased renal elimination.
Question 4: A patient with heart failure has a serum potassium of 3.1 mEq/L and takes digoxin and furosemide. What is the primary concern?
- Furosemide will increase digoxin clearance
- Hypokalemia increases cardiac sensitivity to digoxin toxicity (Correct answer)
- Digoxin will block furosemide's diuretic effect
- Furosemide will raise digoxin protein binding
Correct answer: Hypokalemia increases cardiac sensitivity to digoxin toxicity
Hypokalemia enhances digoxin binding to the Na+/K+-ATPase pump and increases myocardial sensitivity to digoxin, raising the risk of arrhythmias at normal or even subtherapeutic digoxin levels.
Question 5: Which antidiabetic agent class carries the highest risk of hypoglycemia when used as monotherapy?
- SGLT-2 inhibitors
- DPP-4 inhibitors
- Sulfonylureas (Correct answer)
- GLP-1 receptor agonists
Correct answer: Sulfonylureas
Sulfonylureas stimulate insulin secretion independently of blood glucose levels, making hypoglycemia a significant risk even without co-administration of other agents.
Question 6: Which pharmacokinetic change is most commonly observed in elderly patients and requires medication dose adjustment?
- Increased hepatic first-pass metabolism
- Increased renal clearance due to compensatory hyperfiltration
- Decreased renal clearance due to reduced GFR (Correct answer)
- Increased volume of distribution for water-soluble drugs
Correct answer: Decreased renal clearance due to reduced GFR
Age-related decline in glomerular filtration rate (GFR) decreases renal drug clearance, necessitating dose reductions for renally eliminated medications in elderly patients.
Question 7: A patient on an MAOI is given meperidine for pain. What potentially fatal reaction may occur?
- Neuroleptic malignant syndrome
- Serotonin syndrome (Correct answer)
- Malignant hyperthermia
- Anticholinergic toxidrome
Correct answer: Serotonin syndrome
Meperidine inhibits serotonin reuptake; combined with an MAOI that prevents serotonin breakdown, this results in serotonin syndrome, characterized by hyperthermia, agitation, and neuromuscular abnormalities.
MTM Pharmacotherapy Review & Drug Interactions 3
A patient with chronic kidney disease (eGFR 20 mL/min) is taking gabapentin.
What dose adjustment is required?