Quinidine Rifampicin

Clinically important, potentially hazardous interactions with amiodarone, astemizole, bepridil, carbamazepine, chloroquine, cisapride, clarithromycin, dihydroergotamine, disopyramide, ergotamine, grapefruit juice, halofantrine, haloperidol, itraconazole, ketoconazole, methadone, moxifloxacin, phenobarbital, phenytoin, pimozide, procainamide, quinidine, rifampicin, ritonavir, sotalol, St John s wort, telithromycin, terfenadine, voriconazole... 

Displacement of bilirubin from its albmnin bond. Various endogenous substances (e. g. long-chain fatty acids and bile acids) or exogenous compounds (e. g. medication, such as ampicillin, ajma-line, quinidine, furosemide, indomethadn, probenecid, rifampicin, sulphonamide etc., and X-ray contrast media) can compete with bilirubin, not only with respect to its specific binding site, but also for its carrier protein. 

The metabolism of quinidine is enhanced by drugs that induce hepatic microsomal drug-metabolizing enzymes (67), such as rifampicin (77) and phenytoin and pheno-barbital (78). This leads to an increase in the first-pass metabolism of quinidine, and thus increased requirements of oral quinidine but little change in intravenous dosages. 

Enzyme inhibitors, such as cimetidine and ketoconazole, increase the toxicity of quinine or quinidine (43), while enzyme inducers, such as rifampicin, reduce the toxic effects (44). 

Quinidine plasma concentrations can be lowered by rifampicin because of enzyme induction (125). 

Figure 12.4 Influence of rifampicin and quinidine on concentrations of Dg2 in perfusate after addition of 10 ug of digoxin to the perfusate. Values are mean SD, n = 6 per group no liver, n = 3. p<0.05 fxO.Ol for values com pared to control. From Ref. [29].

CYP2C19 CYP2D6 diazepam, imipramine, 5-mephenytoin, omeprazol, proguanil, propranolol codeine, debrisoquine, dextromethorphan, flecainide, paroxetine, perphenazine, thioridazine carbamazepine, rifampicin cimetidine, felbamate fluoxetine, paroxetine, quinidine... 

The serum levels and therapeutic effects of quinidine can be markedly reduced by rifampicin. 

It was noted that the eontrol of ventricular arrhythmia deteriorated in a patient taking quinidine sulfate 800 mg daily within a week of starting to take rifampicin 600 mg daily. His serum quinidine level fell from 4 to... 

Rifampicin is a potent enzyme-inducer, which markedly increases the metabolism of the quinidine by 3-hydroxylation and N-oxidation, thereby reducing its levels and effects. It has been suggested that two of the quinidine metabolites (3-hydroxyquinidine and 2-oxoquinidinone) may be active, which might, to some extent, offset the effects of this interaction. 

Ahmad D, Ivfediur P, Ahuja S, Henderson R, Carruthers G. Rifampicin-quinidine interaction. BrJDis Chest( 979) 73,409-11. 

Damkier P, Hansen LL, Brosen K. Rifampicin treatment greatly increases the apparent oral clearance of quinidine. Pharmacol Toxicol (1999) 85,257- 2. 

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