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NAPLEX Chapter 2 MUST know drug interactions Questions and and answers (1
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NAPLEX Chapter 2 MUST know druginteractions
Common CV drug interactions (5) - ✅✅ -- Amiodarone/dronedarone + warfarin
- Amiodarone + digoxin
- Digoxin + loop diuretics
- Verapamil/Diltiazem + other drugs that ↓HR
- Statins + CYP 3A4 strong inhibitors
Amiodarone/Dronedarone + Warfarin - ✅✅-Amiodarone= 2C9 inhibitor
Warfarin= 2C9 substrate
Amiodarone ↓ warfarin metabolism (increased warfarin levels) → ↑INR levels → ↑
risk of bleeding
If using Amiodarone 1st: start low dose warfarin ≤ 5mg
If using Warfarin 1st: ↓ Warfarin dose 30-50% when starting Amiodarone depending
on INR
Monitor:
- INR (adjust as needed)
- Check for other Amiodarone DDIs
Amiodarone + Digoxin - ✅✅-Amiodarone= P-gp inhibitor
Digoxin= P-gp substrate
Amiodarone ↓ digoxin metabolism (increased digoxin ADRs/toxicity) → both ↓HR, ↑
risk bradycardia, arrhythmia, fatality
If using Amiodarone 1st: start low dose digoxin ≤ 0.125 mg
If using Digoxin 1st: ↓ Digoxin dose 50%
Monitor
- Symptoms of digoxin toxicity (nausea, anorexia, HR)
- Check for other drugs that ↓HR
- Switch to BB or Non-DHP CCB if digoxin is being used for rate control
Digoxin + Loop Diuretics - ✅✅ -Loops ↓ K, Mg, Ca, and Na
Low K and Mg cause digoxin toxicity
Digoxin is cleared by P-gp and directly excreted by kidneys (renal impairment ↑
digoxin levels and toxicity risk)
, Monitor
- Symptoms of digoxin toxicity (nausea, anorexia, HR)
- Check for other drugs that ↓HR
- Switch to BB or Non-DHP CCB if digoxin is being used for rate control (preferred
over digoxin for rate control)
- Check electrolytes and adjust if low
- Renal impairment: ↓ digoxin dose or frequency or discontinue
Statins + CYP 3A4 strong inhibitors (G <3 PACMAN) - ✅✅-↑ levels of statins that
are CYP 3A4 substrates (Simvastatin, Atorvastatin, Lovastatin - SAL) → ↑risk of
myopathy/rhabdomyolysis
Monitor:
- use lower doses of SAL statins
- recommend statins not metabolized by CYP enzymes (pravastatin, rosuvastatin,
pitavastatin)
- avoid grapefruit juice with CYP 3A4 substrates
- Drugs with specific instructions to avoid grapefruit juice: simvastatin, lovastatin,
nifedipine, and tacrolimus
✅✅
Diltiazem/Verapamil + Other drugs that ↓HR (Amiodarone, Digoxin, BBs,
Dexmedetomidine, Clonidine) - -Additive effect with other drugs that ↓HR
Monitor:
- HR
Common inhibitors that increase substrate drugs drug interactions (6) - ✅✅-- CYP
3A4 inhibitors (PS PORCS) + CYP 3A4 substrates
- Valproate + Lamotrigine
- MAO inhibitors + drugs that ↑ Epi, NE, and DA + drugs that ↑5HT
- MAO inhibitors + Tyramine rich foods
- CYP 2D6 inhibitors + CYP 2D6 substrates
- CYP 3A4 inhibitors & P-gp inhibitors + Calcineurin inhibitors
CYP 3A4 inhibitors (PS PORCS) + CYP 3A4 substrates - ✅✅-↓ substrate
metabolism → ↑ADRs/toxicity
Monitor:
- drug levels
- side effects
*Do not use CYP 3A4 inhibitors with opioids metabolized by CYP 3A4 → can be
fatal*
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