Drug interactions

Question 1

amiodarone + warfarin

Answer 1

DDI: CYP2C9 interaction
If starting warfarin, initiate >=5 mg
Dec warfarn dose by 30-50%, depending on INR

Question 2

warfarin + digoxin

Answer 2

If starting digoxin, use 0.125mcg
Dec digoxin dose by 50%
Monitor 1) digoxin toxicity AND 2) HR (normal 60-100)

digoxin toxicity: N/V, visual disturbances
HR: meds that dec HR (BB, non-DHP CCB, clonidine, Precedex)

Question 3

digoxin + loop diuretics

Answer 3

loop diuretics: dec K, Mg, Ca, Na

DDI: digoxin toxicity risk inc by low K, Mg AND high Ca

monitor 1) electrolytes and 2) renal impairment
Note: HF and renal impairment often occur together

Question 4

concomitant use of drugs that dec HR

Answer 4

meds that dec HR: BB, non-DHP (verapamil, dilitzem), clonidine, Precedex

DDI: additive effects when used together

monitor: HR

Question 5

statins + strong CYP3A4 inhibitors

strong CYP3A4 inhib = G <3 PACMAN

Answer 5

Simvastatin, lovastastin, atorvastatin
Non-CYP substrates: pitavastatin, pravastatin, rosuvastatin

Inc substrate levels, increase