Common Drug Interactions

Question 1

Amiodarone and Warfarin

Answer 1

Amiodarone inhibits multiple enzymes including CYP2C9 resulting in decreased warfarin metabolism and increased INR.

Question 2

Amiodarone and Digoxin

Answer 2

Amiodarone inhibits P-gp, which digoxin is a P-gp substrate. Results in increased toxicity of digoxin and decreased excretion. Combined, may decrease HR (bradycardia), and increase chances of arrhythmias and fatality.

Question 3

Digoxin and Loop Diuretic

Answer 3

Loop diuretics decrease K, Mg, Ca, and Na levels which may increase risk of toxicity and worsen arrhythmias.

Question 4

Diltiazem/Verapamil and Other drugs that decrease heart rate

Answer 4

Additive effects can lead to bradycardia. Drugs may include amiodarone, digoxin, dexmedetomidine, beta blockers and clonidine.

Question 5

Statins and CYP3A4 inhibitors

Answer 5

Increasing levels of statins (lovastatin, simvastatin and atorvastatin) will lead to increased risk of myopathy, rhabdomyolysis and acute renal failure. Switch to other statins such as pitavastatin, pravastatin, rosuvastatin).

Question 6

Warfarin and CYP2C9 Inducers/Inhibitors

Answer 6

Inducers: decreases warfarin and INR levels. Increased risk of clotting.

Inhibitors: increases warfarin and INR and risk for bleed.

Question 7

Valproate and Lamotrigine

Answer 7

Valproate is an inhibitor of lamotrigine metabolism.

Leads to increasing levels of lamotrigine and the risk of skin reactions (SJS/TEN). Risk is highest in pediatrics.

Question 8

MAOIs + Drugs increasing Epi, NE, and DA or Drugs that increase 5HT

Answer 8

Epi, NE, DA: increases risk of hypertensive crisis.

5HT: serotonin syndrome

Question 9

MAOIs + Tyramine rich foods

Answer 9

Tyramine causes increases in NE with risk of hypertensive crisis.

Question 10

CYP3A4/P-GP inhibitors + calcineurin inhibitors OR mTOR Kinase inhibitors

Answer 10

Increases toxicity risk (decreasing drug metabolism)

Question 11

Smoking + some antipsychotics, antidepressants, hypnotics, anxiolytics, caffeine, theophylline, insulin, warfarin (R-isomer)

Answer 11

Smoking induces CYP1A2 (tobacco and MJ)
Smokers who quit: can increase toxicity

Current smoker: decreasing levels

Question 12

PDE-5 Inhibitor and CYP3A4 inhibitors

Answer 12

Decreases of PDE5 metabolism leading to increased side effects (headache, dizziness, flushing)

Question 13

PDE-5 inhibitors and Nitrates

Answer 13

Severe hypotension and potentially death. So stop it. Why are you trying to use them together?

Question 14

PDE-5 Inhibitors and Alpha Blockers

Answer 14

Increased risk of hypotension/orthostasis

Question 15

Drugs that causes prolonged QT interval and Antiarrhythmics, antibiotics/antifungals, antidepressants, antipsychotics, antiemetics, etc.

Answer 15

Increased risk of torsades de pointes

Question 16

Quinolones, tetracyclines, levothyroxine, or oral bisphosphonates and
antiacids, sulcralfates, BABs,, calcium, aluminum, magnesium, iron, phosphate binders, multivitamins

Answer 16

Decreases drug absorption and efficacy