Disopyramide Barbiturates

When two antiarrhythmic dragp are administered concurrently the patient may experience additive effects and is at increased risk for drug toxicity. When quinidine and procainamide are administered with digitalis, tiie risk of digitalis toxicity is increased. Hiarmacologic effects of procainamide may be increased when procainamide is administered with quinidine When quinidine is administered with the barbiturates or cimetidine, quinidine serum levels may be increased. When quinidine is administered with verapamil, there is an increased risk of hypotensive effects. When quinidine is administered with disopyramide, there is an increased risk of increased disopyramide blood levels and/or decreased serum quinidine levels. 

Rifampin is known to induce the hepatic microsomal enzymes that metabolize various drugs such as acetaminophen, oral anticoagulants, barbiturates, benzodiazepines, beta blockers, chloramphenicol, clofibrate, oral contraceptives, corticosteroids, cyclosporine, disopyramide, estrogens, hydantoins, mexiletine, quinidine, sulfones, sulfonylureas, theophyllines, tocainide, verapamil, digoxin, enalapril, morphine, nifedipine, ondansetron, progestins, protease inhibitors, buspirone, delavirdine, doxycycline, fluoroquinolones, losartan, macrolides, sulfonylureas, tacrolimus, thyroid hormones, TCAs, zolpidem, zidovudine, and ketoconazole. The therapeutic effects of these drugs may be decreased. 

DISOPYRAMIDE ANTIEPILEPTICS- BARBITURATES, PHENYTOIN Disopyramide levels are 1 by phenobarbital and primidone Phenobarbital and primidone induce the hepatic metabolism of disopyramide Watch for poor response to disopyramide check serum levels if necessaiy... 

Beta blockers (mainly propranolol) Encalnide and flecalnide Quinidine, procainamide, and disopyramide Propoxyphene Tricyclic antidepressants Others Barbiturates... 

This interaction appears to be established, but its clinical importance is uncertain. The extent to which it would reduce the control of arrhythmias by disopyramide is unknown, but monitor the effects and the serum levels of disopyramide if phenobarbital is added or withdrawn. The manufacturer of disopyramide recommends avoiding using it in combination with inducers of the cytochrome P450 isoenzyme CYP3A, such as phenobarbital. Other barbiturates would be expected to interact similarly. 

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