Quinidine Felodipine

Drugs that may affect barbiturates include alcohol, charcoal, chloramphenicol, MAO inhibitors, rifampin, and valproic acid. Drugs that may be affected by barbiturates include acetaminophen, anticoagulants, beta blockers, carbamazepine, chloramphenicol, clonazepam, oral contraceptives, corticosteroids, digitoxin, doxorubicin, doxycycline, felodipine, fenoprofen, griseofulvin, hydantoins, methoxyflurane, metronidazole, narcotics, phenmetrazine, phenylbutazone, quinidine, theophylline, and verapamil. 

Itraconazole Alfentanil, alprazolam, astemizole, atorvastatin, buspirone, cisapride, cyclosporine, delavirdine, diazepam, digoxin, felodipine, indinavir, loratadine, lovastatin, midazolam, nisoldipine, phenytoin, quinidine, ritonavir, saquinavir, sildenafil, simvastatin, sirolimus, tacrolimus, triazolam, verapamil, warfarin... 

CYP3A4 Alfentanil Alprazolam Astern izole Carbamazepine Cisapride Cyclosporine Diltiazem Erythromycin Felodipine Fluconazole Itraconazole Ketoconazole Lidocaine Lova statin Midazolam Nifedipine Quinidine Simvastatin Tacrolimus Terfenadine Verapamil... 

Cardiac drugs Amiodarone, " carvedilol, diltiazem, " dipyridamole, felodipine, nifedipine, propranolol, propafenone, quinidine, verapamil "... 

A few patients have shown increased serum quinidine levels when stopping nifedipine, but in others no interaction has occurred and one study even suggests that quinidine serum levels may be slightly raised by nifedipine. Nifedipine levels may be modestly raised by quinidine. Verapamil reduces the clearance of quinidine and in one patient the serum quinidine levels doubled and quinidine toxicity developed. Acute hypotension has also been seen in three patients taking quinidine when they were given verapamil intravenously. Felodipine and nisoldipine appear not to interact, and the situation with diltiazem is unclear. 

Felodipine 10 mg daily for 3 days was found to have no clinically significant effect on the pharmacokinetics or haemodynamic and ECG effects of a single 400-mg dose of quinidine in 12 healthy subjects. Felodipine did cause a modest 22% decrease in the AUC of the quinidine metabolite 3-hydroxyquinidine. ... 

What is known about the interaction between quinidine and verapamil suggests that a reduction in the dosage of the quinidine may be needed to avoid toxicity. If the verapamil is given intravenously, use with caution and be alert for evidence of acute hypotension. Monitor the effects of concurrent use closely. There is actually a fixed dose preparation containing verapamil and quinidine (Cordichin) available in Germany, which is used for the management of atrial fibrillation. No interaction apparently occurs between quinidine and felodipine or nisoldipine. The situation with diltiazem is as yet uncertain but be alert for the need to reduce the quinidine dosage. 

Bailey DG, Freeman DJ, Melendez LJ, Kreeft JH, Edgar B, CarrutheiB SG. Quinidine interaction with nifedipine and felodipine pharmacokinetic and pharmacodjynamic evaluaticxi. Clin Pharmacol Ther (1993) 53, 354-9. 

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