Drug Interactions between amlodipine / atorvastatin and Mudrane GG

GENERALLY AVOID: Potent inducers of CYP450 3A4 may significantly decrease the plasma concentrations of calcium channel blockers, the majority of which are primarily metabolized by the isoenzyme. Undetectable plasma levels have been reported for some calcium blockers when given orally.

MANAGEMENT: Concomitant use of calcium channel blockers with potent CYP450 3A4 inducers should generally be avoided. If coadministration is necessary, pharmacologic response should be monitored more closely following the initiation or discontinuation of the CYP450 3A4 inducer, and the CCB dosage adjusted accordingly.

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MONITOR: Barbiturates may decrease serum levels and therapeutic effects of the methylxanthines. The mechanism is barbiturate induction of CYP450 3A4 and 1A2 hepatic metabolism of methylxanthines.

MANAGEMENT: Close observation for clinical and laboratory evidence of decreased methylxanthine effect is indicated if these drugs must be used together. Patients should be advised to notify their physician if they experience a worsening of their respiratory symptoms.

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MONITOR: Coadministration with inducers of CYP450 3A4 may decrease the plasma concentrations of atorvastatin and its active metabolites, all of which are substrates of the isoenzyme. When atorvastatin (40 mg/day) was coadministered for 28 days with the potent CYP450 3A4 inducer phenytoin (4 mg/kg/day) in healthy volunteers (n=44), atorvastatin peak plasma concentration (Cmax) and systemic exposure (AUC) decreased by an average of 24% and 54%, respectively. The Cmax of two active metabolites, 2-hydroxy- and 4-hydroxyatorvastatin, also decreased by an average of 22% and 52%, respectively, while AUC decreased by an average of 53% and 44%, respectively. Consistent with the observed pharmacokinetic interaction, there have been isolated reports of reduced efficacy of atorvastatin in the presence of phenytoin, followed by improved cholesterol levels after discontinuation of phenytoin. In another study, coadministration of the mixed CYP450 3A4 inducer/inhibitor efavirenz (600 mg once daily for 15 days) with atorvastatin (10 mg daily during the last 4 days of efavirenz) in 14 healthy volunteers resulted in median decreases of 43% in atorvastatin AUC and 34% in total active atorvastatin (parent drug + active metabolites) AUC. However, the median LDL decrease was not significantly different during coadministration with efavirenz compared to atorvastatin administered alone (-29 versus -22, respectively). Atorvastatin did not affect the AUC of efavirenz. In a study of patients with non-small cell lung cancer receiving the CYP450 3A4 inducer bexarotene (400 mg/m2 orally once a day) plus either paclitaxel/carboplatin or cisplatin/vinorelbine chemotherapy, treatment with atorvastatin or fenofibrate was given to manage bexarotene-induced hyperlipidemia. Investigators reported that bexarotene decreased mean atorvastatin systemic exposure (dose-corrected AUC) by approximately 50%, whereas atorvastatin had no significant effect on bexarotene plasma concentrations. In 16 study subjects administered etravirine with atorvastatin 40 mg once a day, atorvastatin AUC decreased by 37%, while Cmax and AUC of 2-hydroxy-atorvastatin increased by 76% and 27%, respectively. Atorvastatin did not significantly affect the pharmacokinetics of etravirine.

MANAGEMENT: The potential for diminished pharmacologic effects of atorvastatin should be considered during coadministration with CYP450 3A4 inducers. Alternative agents with no or minimal CYP450 3A4 induction potential are recommended whenever possible. Otherwise, pharmacologic response to atorvastatin should be closely monitored, and the dosage adjusted as necessary. A statin that is not metabolized by CYP450 3A4 such as fluvastatin, pitavastatin, pravastatin, or rosuvastatin may also be substituted for atorvastatin when used with certain enzyme inducers.

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MONITOR: Coadministration with inhibitors of CYP450 3A4 may increase the plasma concentrations of HMG-CoA reductase inhibitors (i.e., statins) that are metabolized by the isoenzyme. Lovastatin and simvastatin are particularly susceptible because of their low oral bioavailability, but others such as atorvastatin and cerivastatin may also be affected. High levels of HMG-CoA reductase inhibitory activity in plasma is associated with an increased risk of musculoskeletal toxicity. Myopathy manifested as muscle pain and/or weakness associated with grossly elevated creatine kinase exceeding ten times the upper limit of normal has been reported occasionally. Rhabdomyolysis has also occurred rarely, which may be accompanied by acute renal failure secondary to myoglobinuria and may result in death. Clinically significant interactions have been reported with potent CYP450 3A4 inhibitors such as macrolide antibiotics, azole antifungals, protease inhibitors and nefazodone, and moderate inhibitors such as amiodarone, cyclosporine, danazol, diltiazem and verapamil.

MANAGEMENT: Caution is recommended if atorvastatin, cerivastatin, lovastatin, simvastatin, or red yeast rice (which contains lovastatin) is prescribed with a CYP450 3A4 inhibitor. It is advisable to monitor lipid levels and use the lowest effective statin dose. All patients receiving statin therapy should be advised to promptly report any unexplained muscle pain, tenderness or weakness, particularly if accompanied by fever, malaise and/or dark colored urine. Therapy should be discontinued if creatine kinase is markedly elevated in the absence of strenuous exercise or if myopathy is otherwise suspected or diagnosed. Fluvastatin, pravastatin, and rosuvastatin are not expected to interact with CYP450 3A4 inhibitors.

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Ephedrine-methylxanthine combinations are used for the treatment of asthma but the efficacy of the combination has been questioned. This combination may lead to increased xanthine side effects. The mechanism is unknown, but may be related to synergistic pharmacologic effects. Patients using this combination should be closely monitored for side effects such as nausea, vomiting, tachycardia, nervousness, or insomnia. If side effects are noted, the dosage of the xanthine may need to be decreased.

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