Veterinary Drug Handbook (VDH) is the reference veterinarians turn to when they want an independent source of information on the drugs that are used in veterinary medicine today.

LIDOCAINE HCL

Chemistry - A potent local anesthetic and antiarrhythmic agent, lidocaine HCl occurs as a white, odorless, slightly bitter tasting, crystalline powder with a melting point between 74° - 79°C and apKa of 7.86. It is very soluble in water and alcohol. The pH of the commercial injection is adjustedto 5 - 7, and the pH of the commercially available infusion in dextrose 5% is adjusted to 3.5 - 6.
Lidocaine is also known as lignocaine HCl.

Storage, Stability, Compatibility

Lidocaine for injection should be stored at temperatures lessthan 40°C and preferably between 15-30°C; avoid freezing.
Lidocaine is compatible with most commonly used IV infusion solutions, including D5W, lactated Ringer's, saline, and combinations of these. It is also reportedly physically compatible with:aminophylline, bretylium tosylate, calcium chloride/gluceptate/gluconate, carbenicillin disodium, chloramphenicol sodium succinate, chlorothiazide sodium, cimetidine HCl, dexamethasone sodiumphosphate, digoxin, diphenhydramine HCl, dobutamine HCl, ephedrine sulfate, erythromycinlactobionate, glycopyrrolate, heparin sodium, hydrocortisone sodium succinate, hydroxyzine HCl, insulin (regular), mephentermine sulfate, metaraminol bitartrate, methicillin sodium, metoclopramide
HCl, nitrofurantoin sodium, oxytetracycline HCl, penicillin G potassium, pentobarbital sodium, phenylephrine HCl, potassium chloride, procainamide HCl, prochlorperazine edisylate, promazine
HCl, sodium bicarbonate, sodium lactate, tetracycline HCl, verapamil HCl, and Vitamin B-Complexw/C.
Lidocaine may not be compatible with dopamine, epinephrine, isoproterenol or norepinephrineas these require low pH's for stability. Lidocaine is reportedly incompatible with: ampicillinsodium, cefazolin sodium, methohexital sodium, or phenytoin sodium. Compatibility is dependentupon factors such as pH, concentration, temperature, and diluents used and it is suggested toconsult specialized references for more specific information.

Pharmacology - LIDOCAINE HCL

Lidocaine is considered to be a class IB (membrane-stabilizing) antidysrhythmicagent. It is thought that lidocaine acts by combining with fast sodium channels when inactive whichinhibits recovery after repolarization. Class IB agents demonstrate rapid rates of attachment anddissociation to sodium channels. At therapeutic levels, lidocaine causes phase 4 diastolicdepolarization attenuation, decreased automaticity, and either a decrease or no change in membraneresponsiveness and excitability. These effects will occur at serum levels that will not inhibit theautomaticity of the SA node, and will have little effect on AV node conduction or His-Purkinjeconduction.
Uses, Indications - Besides its use as a local and topical anesthetic agent, lidocaine is used to treatventricular arrhythmias, principally ventricular tachycardia and ventricular premature complexes inall species. Cats tend to be rather sensitive to the drug and some clinicans feel that it should not beused in this species as an antiarrhythmic.

Pharmacokinetics - LIDOCAINE HCL

Lidocaine is not effective orally as it has a high first-pass effect. If very highoral doses are given, toxic symptoms occur (due to active metabolites?) before therapeutic levels canbe reached. Following a therapeutic IV bolus dose, the onset of action is generally within 2 minutesand has a duration of action of 10-20 minutes. If a constant infusion is begun without an initial IVbolus it may take up to an hour for therapeutic levels to be reached. IM injections may be givenevery 1.5 hours in the dog, but because monitoring and adjusting dosages are difficult, it should bereserved for cases where IV infusions are not possible.
After injection, the drug is rapidly redistributed from the plasma into highly perfused organs(kidney, liver, lungs, heart) and is distributed widely throughout body tissues. It has a high affinityfor fat and adipose tissue and is bound to plasma proteins, primarily alpha1-acid glycoprotein. Ithas been reported that lidocaine binding to this protein is highly variable and concentration dependent in the dog and may be higher in dogs with inflammatory disease. Lidocaine is distributedinto milk. The apparent volume of distribution (Vd) has been reported to be 4.5 L/kg in the dog.
Lidocaine is rapidly metabolized in the liver to active metabolites (MEGX and GX). The terminalhalf-life of lidocaine in humans is 1.5-2 hours and has been reported to be 0.9 hours in the dog.
The half-lives of lidocaine and MEGX may be prolonged in patients with cardiac failure or hepaticdisease. Less than 10% of a parenteral dose is excreted unchanged in the urine.
Contraindications/Precautions - Cats tend to be more sensitive to the CNS effects of lidocaine;use with caution. Lidocaine is contraindicated in patients with known hypersensitivity to the amideclass local anesthetics, a severe degree of SA, AV or intraventricular heart block (if not beingartificially paced), or Adams-Stokes syndrome. The use of lidocaine in patients with Wolff-Parkinson-White (WPW) syndrome is controversial. Some manufacturers state its use iscontraindicated, but several physicians have used the drug in people.
Lidocaine should be used with caution in patients with liver disease, congestive heart failure, shock, hypovolemia, severe respiratory depression, or marked hypoxia. It should be also be used withcaution in patients with bradycardia or incomplete heart block having VPC's, unless the heart rate isfirst accelerated. Patients susceptible to developing malignant hyperthermia should receive lidocainewith intensified monitoring.

Adverse Effects, Warnings

At usual doses and if the serum level remains within the proposedtherapeutic range (1 - 5 micrograms/ml), serious adverse reactions are quite rare. The most commonadverse effects reported are dose related (serum level) and mild. CNS signs include drowsiness, depression, ataxia, muscle tremors, etc. Nausea and vomiting may occur, but are usually transient.
Adverse cardiac effects generally only occur at high plasma concentrations and are usuallyassociated with PR and QRS interval prolongation and QT interval shortening. Lidocaine mayincrease ventricular rates if used in patients with atrial fibrillation. If an IV bolus is given toorapidly, hypotension may occur.
Be certain not to use the product which contains epinephrine intravenously.
Overdosage - In dogs, if serum levels of >8 micrograms/ml are attained, toxicity may result.
Symptoms may include ataxia, nystagmus, depression, seizures, bradycardia, hypotension and, atvery high levels, circulatory collapse. Because lidocaine is rapidly metabolized, cessation of therapyor reduction in infusion rates with monitoring may be all that is required for minor symptoms.
Seizures or excitement may be treated with diazepam, or a short or ultrashort acting barbiturate.
Longer acting barbiturates (e.g., pentobarbital) should be avoided. Should circulatory depressionoccur, treat with fluids, pressor agents and if necessary, begin CPR.

Drug Interactions

Lidocaine levels or effects may be increased by concomitant administration ofcimetidine or propranolol.
Other antiarrhythmics such as procainamide, quinidine, propranolol, phenytoinadministered with lidocaine may cause additive or antagonistic cardiac effects and toxicity may beenhanced. Phenytoin when given IV with lidocaine may cause increased cardiac depression. Large doses of lidocaine may prolong succinylcholine-induced apnea.
Laboratory Interactions - Lidocaine may cause increased creatine kinase levels (CK).

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