Class IB antiarrhythmics

Glass IB Antiarrhythmic Agents. Class IB antiarrhythmic agents produce less inhibition of the inward sodium current than Class lA agents. In normal myocardial tissue, phase 0 may be unaffected or minimally depressed. However, in ischemic or infarcted tissue, phase 0 is depressed. Myocardial tissue exposed to Class IB agents exhibits decreased automaticity, shortened action potential duration, ie, shortened repolarization, and shortened refractory period. Excitability of the myocardium is not affected and conduction velocity is increased or not modified. The refractory period is shortened less than its action potential duration, thus the ratio of refractory period to action potential duration is increased by these agents. The net effect is increased refractoriness. The PR and QT intervals of the ECG are shortened and the QRS interval is unchanged (1,2). 

Electrophysiology- Mexiletine is a local anesthetic and a Class IB antiarrhythmic compound with electrophysiologic properties similar to lidocaine. 

Khan MH. Oral class IB antiarrhythmics what is new Curr Opin Cardiol 2004 19(1) 47-51. 

When used with other class IB antiarrhythmic drugs, tocainide toxicity may be increased without significant gain in antiarrhythmic efficacy. 

The antiarrhythmic of choice for SuVT is lidocaine because of its fast onset and ease of administration. Lidocaine is a class IB antiarrhythmic that inhibits sodium ion channels, decreasing the action potential duration and effective... 

Mechanism of action Class IB antiarrhythmics inhibit sodium ion channels and decrease the action potential duration and effective refractory period. 

Lidocaine (lignocaine) is a class Ib antiarrhythmic agent. Its antiarrhythmic action is mediated mainly within the non-nodal tissue of the ventricles and... 

Phenytoin is another class Ib antiarrhythmic drug that is used mainly for the treatment of cardiac... 

Synonyms Dilocaine Lidoderm Lidoject-1 Lignocaine Nervocaine Nulicaine Octocaine Solarcaine Xylocaine Xylocard Chemical/Pharmaceutical/Other Class Amide-type local anesthetic Class IB antiarrhythmic Chemical Structure ... 

Repeated doses of activated charcoal may enhance elimination. Serum electrolytes should be monitored in all serious exposures. Intravenous administration of sodium bicarbonate may decrease toxicity. Hypotension can be treated with fluids and vasopressors if needed. Ventricular dysrhythmias can be treated with class IB antiarrhythmics such as phenytoin or lido-caine. Persistent bradycardia and third-degree heart block are indications for insertion of a temporary pacemaker. Seizures can be treated with diazepam. If seizures are uncontrolled, phenobarbital or phenytoin can be administered. 

Additive toxicity without therapeutic benefit when combined with other class Ib antiarrhythmics. 

Lidocaine [2-(diethylamino)-N-(2, 6-dimethylphenyl) acetamide monohydrochloride] is the most commonly used amino amide-type local anesthetic. Lidocaine is very lipid soluble and, thus, has a more rapid onset and a longer duration of action than most amino ester-type local anesthetics, such as procaine and tetracaine. It can be administered parenterally (with or without epinephrine) or topically either by itself or in combination with prilocaine or etidocaine as a eutectic mixture that is very popular with pediatric patients. The use of lidocaine-epinephrine mixtures should be avoided, however, in areas with limited vascular supply to prevent tissue necrosis. Lidocaine also frequently is used as a class IB antiarrhythmic agent for the treatment of ventricular arrhythmias, both because it binds and inhibits sodium channels in the cardiac muscle and because of its longer duration of action than amino ester-type local anesthetics. 

Torsade de pointes has been described in a patient taking amiodarone and mexiletine (a class Ib antiarrhythmic). The manufacturers of mexiletine say that this seems to be an isolated case. ... 

Class Ib antiarrhythmics are usually associated with shortening of the QT interval, and could therefore be expected to reduce the QT prolongation and risk of torsade de pointes seen with amiodarone alone (for examples of this effect of mexiletine see also Mexiletine + Beta blockers, p.268 and Mexiletine + Quinidine , p.269. However, note that the UK manufacturer of mexiletine says that it may exacerbate arrhythmias [as all antiarrhythmics may], but also that it may be used concurrently with amiodarone. The two drugs have been used together successfully. ... 

Lidocaine, like other local anesthetics, binds axonal membrane voltage-gated fast Na channels and thus prevents Na+ transport across the channels, thus inhibiting cell membrane depolarization. It is by this same mechanism that lidocaine exerts its effect as a class Ib antiarrhythmic to inhibit cardiac smooth muscle excitability and as an anti-epileptic drug to inhibit cortical excitability. Its lipophilic aromatic group allows the molecule to penetrate the nerve membrane, while its hydrophilic charged amine group is the portion of the molecule that actually binds the Na chaimel [1-3]. 

Mexiletine 5 is a class Ib antiarrhythmic ficensed for use in patients with life-threatening irregular heartbeat and may also be of use in the control of refractory pain. 

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