Lidocaine Phenytoin

Class IB drugs like lidocaine, phenytoin or mex-iletine preferentially bind to the inactivated state. Lidocaine, a local anaesthetic, can be used intravenously for antiarrhythmic treatment. It is one of the classical dtugs used in emergency medicine for the... 

IB (tocainide, lidocaine, phenytoin, mexiletine) - Depress phase 0 slightly and may shorten the action potential duration. Although arrhythmia is not a labeled indication for phenytoin, it is commonly used in treatment of digitalis-induced arrhythmias. 

IB Lidocaine Phenytoin Tocainide Moricizine Mexiletine Minimally change V , of phase 0, decrease cardiac action potential duration, decrease inward sodium current in ventricular muscle, increase outward potassium current. 

A B C Blocks Na channels Moderately depresses phase O and lengthens APD, ERP Minimally depresses phase O and shortens APD, ERP Maximally depresses phase O and does not change APD, ERP Quinidine, procainamide Lidocaine, phenytoin Encainde, lorcainide, liecainide... 

Clinically important, potentially hazardous interactions with alcohol, aminophylline, aspirin, chlordiazepoxide, diazepam, lidocaine, phenytoin, propranolol, warfarin... 

B lidocaine, phenytoin Neuron blockers reserpine, guanethidine CCBs verapamil, nifedipine, bepridel... 

Smigol, V. Svec, R Frechet, J.M. J. Novel uniformly sized polymeric stationary phase with hydrophiUzed large pores for direct injection HPLC determination of drugs in biological fluids. J.Liq.Chromatogr., 1994, 17, 891-911 [also aspirin, caffeine, carbamazepine, lidocaine, phenytoin, salicylic acid, theobromine]... 

This class includes lidocaine, phenytoin. tocainide and mexiletine. 

CImetidine Benzodiazepines, lidocaine, phenytoin, quinidine, theophyiiine, warfarin Increased effect due to inhibition of hepatic metabolism... 

A a Eh X 0 a e Eh P) t=L Use with caution in patients over 50 years oid with kidney or liver faiiure. PO/IV/IM. Little plasma protein binding, little metabolism. Cimetidine increases serum concentrations of many drugs (oral anticoagulants, theophylline, lidocaine, phenytoin, benzodiazepines, nifedipine, propranolol) by inhibiting liver P450 enzymes. May inhibit renal tubular secretion of procainamide. ... 

Treat recurrent ventricular tachycardia with lidocaine, phenytoin, or overdrive pacing (p 13). Do not use other type la or Ic agents, because they may worsen cardiac toxicity. 

I b With shortening of action potential Lidocaine, Mexiletine, Tocainide, Phenytoin, Aprindine... 

Alternatively, a continuous magnesium infusion may be initiated after the first bolus, at a rate of 0.5 to 1 g/hour. Alternative treatments include transvenous insertion of a temporary pacemaker for overdrive pacing, which shortens the QT interval and may terminate torsades de pointes intravenous isoproterenol 2 to 10 mcg/minute, to increase the heart rate and shorten the QT interval intravenous lidocaine, which may shorten the duration of ventricular repolarization or intravenous phenytoin, which may also shorten the duration of ventricular repolarization, administered at a dose of 10 to 15 mg/kg infused at a rate of 25 to 50 mg/minute. 

Phenytoin has the same main effects on the heart as lidocaine. Its use is essentially limited, and it is primarily used only as an oral replacement of lidocaine for paroxysmal tachycardia that is caused particularly by intoxication of digitahs drugs. Synonyms of this drug are dilantin and diphenylan. 

Highly protein-bound drugs In vivo, raloxifene did not affect the binding of warfarin, phenytoin, or tamoxifen. However, use caution when raloxifene is coadministered with other highly protein-bound drugs, such as diazepam, diazoxide, and lidocaine. 

Digitalis intoxication Exercise caution in the use of procainamide in arrhythmias associated with digitalis intoxication. Procainamide can suppress digitalis-induced arrhythmias however, if there is concomitant marked disturbance of AV conduction, additional depression of conduction and ventricular asystole or fibrillation may result. Consider use of procainamide only if discontinuation of digitalis, and therapy with potassium, lidocaine, or phenytoin are ineffective. 

The concurrent administration of lidocaine with cimeti-dine but not ranitidine may cause an increase (15%) in the plasma concentration of lidocaine. This effect is a manifestation of cimetidine reducing the clearance and volume of distribution of lidocaine. The myocardial depressant effect of lidocaine is enhanced by phenytoin administration. 

Phenytoin, like lidocaine, usually does not alter the action potential duration or ERP of atrial tissue except at very high concentrations. Atrial conduction velocity is either unchanged or slightly depressed. 

The electrophysiological effects of phenytoin on the His-Purkinje system resemble those of lidocaine that is. 

Phenytoin, like lidocaine, is more effective in the treatment of ventricular than supraventricular arrhythmias. It is particularly effective in treating ventricular arrhythmias associated with digitalis toxicity, acute myocardial infarction, open-heart surgery, anesthesia, cardiac catheterization, cardioversion, and angiographic studies. 

C. Adenosine is a product of the metabolism of adenosine triphosphate. Phenytoin and lidocaine are totally synthetic, while digoxin occurs naturally in plants and quinine occurs in the cinchona tree. 

Omeprazole can inhibit the metabolism of drugs metabolised mainly by the cytochrome P-450 enzyme subfamily 2C (diazepam, phenytoin), but not of those metabolished by subfamilies lA (caffeine, theophylline), 2D (metoprolol, propranolol), and 3A (ciclosporin, lidocaine (lignocaine), quinidine). Since relatively few drugs are metabolised mainly by 2C compared with 2D and 3A, the potential for omeprazole to interfere with the metabolism of other drugs appears to be limited, but the half lives of diazepam and phenytoin are prolonged as much as by cimetidine. 

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