Chapter 3: Common Cardiovascular Drug Interactions

Question 1

Amiodarone + Warfarin

Answer 1

Amiodarone inhibits multiple enzymes, including CYP2C9, which metabolizes the major warfarin isomer (decreased warfarin metabolism=increased INR)

*can be used together for afib and clot risk

Question 2

Amiodarone + Digoxin

Answer 2

Amiodarone inhibits P-gp, digoxin is a p-gp substrate. Causes decreased digoxin excretion and increased ADRs and toxicity
Both drugs reduce HR so increased risk of bradycardia, arrhythmia and fatality

*can be used together amiodarone (rhythm) and digoxin (rate, or symptom improvement in HF)

Question 3

Digoxin + Loop Diuretic

Answer 3

Loops decrease K, Mg, Ca, and Na
Low K, Mg, or Ca will worsen arrhythmias
Digoxin toxicity risk is increased with decreased K and Mg levels and increased Ca levels

Question 4

Drugs that decrease HR

Answer 4

• Diltiazem/verapamil
• BBs
• Clonidine

Additive effects when drugs are used together (normal HR is 60-100bpm)

Question 5

Statins + Strong CYP3A4 inhibitors

Answer 5

Increased levels of CYP3A4 substrates (lovastatin, simvastatin, atorvastatin) = increased myopathy risk; if severe (w/ high CPK) can cause rhabdo with ARF

Question 6

Warfarin + CYP2C9 inhibitors and inducers

Answer 6

Inhibitors = increased levels of warfarin (azoles, bactrim, amiodarone, metronidazole)
Inducers = decreased levels of warfarin (rifampin, st. john's wort)