Common Cardiovascular Drug Interactions

Question 1

Risk:

Amiodarone + Warfarin

Answer 1

• Warfarin is a CYP2C19 Substrate
• Amiodarone inhibits CYP2C19
• Amiodarone decreases warfarin metabolism -> increased INR & bleed risk

Question 2

Solution:

Amiodarone + Warfarin: if using amiodarone 1st and adding warfarin

Answer 2

Start warfarin at a lower dose of </= 5 mg

Question 3

Solution

Amiodarone + Warfarin: if using warfarin 1st and adding amiodarone

Answer 3

Decrease warfarin dose by 30-50%, depending on INR

Question 4

Solution

Amiodarone + Warfarin

Answer 4

Monitor INR, adjust as needed

Question 5

Risk

Amiodarone + Digoxin

Answer 5

• Digoxin is a P-gp substrate
• Amiodarone inhibits P-gp
• Amiodarone decreases digoxin excretion
• increased risk of toxicity: bradycardia, arrhythmia, death

Question 6

Solution

Amiodarone + Digoxin: if using amiodarone 1st and adding digoxin

Answer 6

Start digoxin at a low dose (ex. 0.125mg daily)

Question 7

Solution

Amiodarone + Digoxin: if using digoxin 1st and adding amiodarone

Answer 7

decrease PO digoxin dose by 50%

Question 8

Solution

Amiodarone + Digoxin

Answer 8

• monitor for signs of digoxin toxicity: N/V & vision changes
• Monitor HR
• Check for other HR lowering drugs (BB, clonidine, diltiazem, verapamil, dexmedetomidine (precedex)
• If digoxin is being used for rate control, recommend changing to a BB or non-DHP CCB

Question 9

Risk

Digoxin + Loop Diuretic

Answer 9

• Loop diuretics decrease K, Mg, & Ca -> arrhythmias
• Digoxin toxicity risk is increased with low K & Mg
• Loop diruetics can cause kidney injury -> decreased digoxin clearance -> toxicity

Question 10

Solution

Digoxin + Loop Diuretic

Answer 10

• monitor electorlytes
• renal impairment: decrease digoxin dose/frequency or DC

Question 11

Examples of

Drugs that decrease HR

Answer 11

• Diltiazem
• Verapamil
• BB (-olol)
• Clonidine

Question 12

Risk

Drugs that decrease HR

Answer 12

Additive effects -> bradycardia

Question 13

Solution

Drugs that decrease HR

Answer 13

Monitor HR (normal: 60-100 bpm)

Question 14

Risk

Statins + Strong CYP3A4 inhibitors [protease inhibitors (inc ritonavir), cobicistat, clarithomycin, erythromycin, azole antifungals, cyclosporine, grapefruit]

Answer 14

Increased levels of CYP3A4 substrates (lovastatin, simvastatin, atorvastatin)
* increased myopathy / rhabdomyolysis risk

Question 15

Solution

Statins + Strong CYP3A4 inhibitors [protease inhibitors (inc ritonavir), cobicistat, clarithomycin, erythromycin, azole antifungals, cyclosporine, grapefruit]

Answer 15

Simvastatin and lovastatin are contraindicated with strong CYP3A4 inhibitors

Reccomend statin not metabolized by 3A4
* rosuvastatin
* pravastatin
* pitavastatin

Question 16

Risk

Warfarin + CYP2C9 inhibitors (azole antifungals, SMX/TMP, amiodarone, metronidazole)

Answer 16

increased warfarin levels -> increased INR & bleed risk

Question 17

Solution

Warfarin + CYP2C9 inhibitors (azole antifungals, SMX/TMP, amiodarone, metronidazole)

Answer 17

Monitor INR (normal 2-3)

Question 18

Risk

Warfarin + CYP2C9 inducers (rifampin, St. John’s wort)

Answer 18

Decreased warfarin levels -> decreased INR & increased clot risk

Question 19

Solution

Warfarin + CYP2C9 inducers (rifampin, St. John’s wort)

Answer 19

Montior INR (normal 2-3)