MTM Pharmacotherapy Review & Drug Interactions — Questions and Answers

Question 1: Which of the following medications is most likely to cause a serious drug interaction with warfarin?

Acetaminophen
Simvastatin
Amiodarone (Correct answer)
Lisinopril

Correct answer: Amiodarone

Amiodarone is a potent inhibitor of CYP2C9, the primary enzyme responsible for metabolizing warfarin. When taken together, amiodarone significantly increases warfarin's concentration in the blood, leading to an elevated risk of severe bleeding. Close monitoring and warfarin dose adjustments are critical when these medications are co-administered.

Question 2: What is the primary concern when combining an ACE inhibitor with a potassium-sparing diuretic?

Increased sodium retention
Hypokalemia
Hyperkalemia (Correct answer)
Bradycardia

Correct answer: Hyperkalemia

Both ACE inhibitors and potassium-sparing diuretics independently increase serum potassium levels. When these two drug classes are combined, their additive effects significantly elevate the risk of hyperkalemia, a dangerous condition characterized by excessively high potassium levels in the blood. This can lead to serious cardiac arrhythmias.

Question 3: Which medication is a strong CYP3A4 inhibitor that can increase serum levels of statins?

Metformin
Ketoconazole (Correct answer)
Aspirin
Hydrochlorothiazide

Correct answer: Ketoconazole

Ketoconazole is a strong inhibitor of the CYP3A4 enzyme, which is responsible for the metabolism of many statins (e.g., simvastatin, atorvastatin). By inhibiting this enzyme, ketoconazole prevents the breakdown of statins, leading to increased systemic exposure and higher serum levels. This significantly raises the risk of statin-related adverse effects, particularly myopathy and rhabdomyolysis.

Question 4: Which pharmacokinetic interaction occurs when omeprazole is taken with clopidogrel?

Increased clopidogrel activation
Increased bleeding risk
Reduced clopidogrel efficacy (Correct answer)
No interaction

Correct answer: Reduced clopidogrel efficacy

Omeprazole, a proton pump inhibitor, inhibits the CYP2C19 enzyme, which is crucial for converting clopidogrel into its active antiplatelet metabolite. This inhibition reduces the activation of clopidogrel, thereby decreasing its antiplatelet efficacy. Consequently, patients taking both medications may have an increased risk of cardiovascular events like stent thrombosis.

Question 5: Which class of antidepressants is most associated with significant drug-drug interactions?

SSRIs
MAO inhibitors (Correct answer)
SNRIs
Tricyclic antidepressants

Correct answer: MAO inhibitors

Monoamine oxidase inhibitors (MAOIs) are known for their numerous and potentially severe drug-drug interactions due to their broad effects on neurotransmitter metabolism. They can lead to hypertensive crises when combined with tyramine-rich foods or sympathomimetic drugs, and cause life-threatening serotonin syndrome when co-administered with other serotonergic agents.

Question 6: What type of drug interaction occurs when a medication affects the excretion of another?

Pharmacodynamic
Pharmacokinetic (Correct answer)
Synergistic
Antagonistic

Correct answer: Pharmacokinetic

Pharmacokinetic interactions involve how the body processes a drug, encompassing absorption, distribution, metabolism, and excretion (ADME). When one medication alters the rate at which another drug is excreted from the body, it directly impacts the second drug's concentration and duration of action, fitting the definition of a pharmacokinetic interaction.

Question 7: Which drug is known to decrease the effectiveness of oral contraceptives?

Amoxicillin
Rifampin (Correct answer)
Azithromycin
Cefuroxime

Correct answer: Rifampin

Rifampin is a potent inducer of hepatic cytochrome P450 enzymes, particularly CYP3A4. These enzymes are responsible for metabolizing the estrogen and progestin components of oral contraceptives. By accelerating their metabolism, rifampin significantly reduces the systemic levels of these hormones, thereby decreasing the effectiveness of oral contraceptives and increasing the risk of unintended pregnancy.

Question 8: Which of the following increases the risk of serotonin syndrome when used with SSRIs?

Tramadol (Correct answer)
Acetaminophen
Ibuprofen
Loratadine

Correct answer: Tramadol

Tramadol is a synthetic opioid that also acts as a serotonin-norepinephrine reuptake inhibitor (SNRI). When combined with SSRIs, which also increase serotonin levels in the brain, there is an additive effect on serotonergic activity. This significantly elevates the risk of serotonin syndrome, a potentially life-threatening condition characterized by excessive serotonin in the central nervous system.

Question 9: Which interaction is likely when NSAIDs are combined with antihypertensive medications?

Improved blood pressure control
Reduced blood pressure
Reduced efficacy of antihypertensives (Correct answer)
No change in blood pressure

Correct answer: Reduced efficacy of antihypertensives

NSAIDs can cause sodium and water retention, and they interfere with the production of prostaglandins, which are crucial for maintaining renal blood flow and blood pressure regulation. These physiological effects can counteract the mechanisms of action of many antihypertensive medications, such as diuretics, ACE inhibitors, and ARBs. Consequently, this interaction can lead to an increase in blood pressure, thereby reducing the overall efficacy of the antihypertensive therapy.

MTM Pharmacotherapy Review & Drug Interactions

Which of the following medications is most likely to cause a serious drug interaction with warfarin?