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Author: Admin | 2025-04-28
Monitor INR.Simvastatin, lovastatin, atorvastatinIncreases risk of myopathy and rhabdomyolysis. Onset may be seen within 2 weeks.Simvastatin dosage should not exceed 20 mg/d. Lovastatin dosage should not exceed 40 mg/d. No specific recommended dosage of atorvastatin.Ask patients about muscle pain and weakness.DigoxinSerum digoxin concentrations can increase by up to 104%. Onset can be as early as 2 days.Monitor for GI, neurologic, and cardiac toxicities. Reduce digoxin dose by 50%. Monitor digoxin levels.Calcium channel blockers,Additive effect, which can cause significant bradycardia and AV block.Use combination with caution, especially in patients with underlying sinus node dysfunction or partial AV block.MECHANISMS OF INTERACTIONCytochrome P-450 enzyme system. Amiodarone is metabolized hepatically and serves as a substrate primarily for cytochrome P-450 (CYP) 3A4. In addition, it is a potent inhibitor of CYP 3A4, 2C9, 2D6, and 1A2.2As a result, concurrent use of CYP 3A4 inhibitors can cause levels of amiodarone to increase and the use of CYP 3A4 inducers can result in decreased concentrations of amiodarone. Numerous amiodarone drug interactions are associated with the inhibition of CYP 3A4 and other CYP isoenzymes by amiodarone, resulting in increased serum concentrations of the other medications (see Tables 1 through 5 for examples).Transporter proteins. P-glycoproteins act as energy-dependent transmembrane efflux pumps that play a role in the distribution of medications such as digoxin, cyclosporine, and protease inhibitors.2 These proteins are widely distributed in the intestines, but they are also located among the endothelial cells of the blood-brain barrier, kidneys, liver, and other organs. Amiodarone can inhibit P-glycoprotein expression, which results in supratherapeutic levels of agents absorbed via this pathway.Pharmacodynamic interaction. This interaction occurs when the pharmacologic response to a given agent is changed by the actions of another drug.2 An example of this type of interaction would be 2 drugs that produce additive effects. Table 1 -Amiodarone and CV
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