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 a pKa of 7.86. It is very soluble in water and alcohol. The pH of the commercial injection is adjusted to 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 less than 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 sodium phosphate, digoxin, diphenhydramine HCl, dobutamine HCl, ephedrine sulfate, erythromycin lactobionate, 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-Complex w/C.
Lidocaine may not be compatible with dopamine, epinephrine, isoproterenol or norepinephrine as these require low pH’s for stability. Lidocaine is reportedly incompatible with: ampicillin sodium, cefazolin sodium, methohexital sodium, or phenytoin sodium. Compatibility is dependent upon factors such as pH, concentration, temperature, and diluents used and it is suggested to consult specialized references for more specific information.
Pharmacology - Lidocaine is considered to be a class IB (membrane-stabilizing) antidysrhythmic agent. It is thought that lidocaine acts by combining with fast sodium channels when inactive which inhibits recovery after repolarization. Class IB agents demonstrate rapid rates of attachment and dissociation to sodium channels. At therapeutic levels, lidocaine causes phase 4 diastolic depolarization attenuation, decreased automaticity, and either a decrease or no change in membrane responsiveness and excitability. These effects will occur at serum levels that will not inhibit the automaticity of the SA node, and will have little effect on AV node conduction or His-Purkinje conduction.
Uses/Indications - Besides its use as a local and topical anesthetic agent, lidocaine is used to treat ventricular arrhythmias, principally ventricular tachycardia and ventricular premature complexes in all species. Cats tend to be rather sensitive to the drug and some clinicans feel that it should not be used in this species as an antiarrhythmic.
Pharmacokinetics - Lidocaine is not effective orally as it has a high first-pass effect. If very high oral doses are given, toxic symptoms occur (due to active metabolites?) before therapeutic levels can be reached. Following a therapeutic IV bolus dose, the onset of action is generally within 2 minutes and has a duration of action of 10-20 minutes. If a constant infusion is begun without an initial IV bolus it may take up to an hour for therapeutic levels to be reached. IM injections may be given every 1.5 hours in the dog, but because monitoring and adjusting dosages are difficult, it should be reserved 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 affinity for fat and adipose tissue and is bound to plasma proteins, primarily alpha1-acid glycoprotein. It has 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 distributed into 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 terminal half-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 hepatic disease. 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 amide-class local anesthetics, a severe degree of SA, AV or intraventricular heart block (if not being artificially paced), or Adams-Stokes syndrome. The use of lidocaine in patients with Wolff-Parkinson-White (WPW) syndrome is controversial. Some manufacturers state its use is contraindicated, 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 with caution in patients with bradycardia or incomplete heart block having VPC’s, unless the heart rate is first accelerated. Patients susceptible to developing malignant hyperthermia should receive lidocaine with intensified monitoring.
Adverse Effects/Warnings - At usual doses and if the serum level remains within the proposed therapeutic range (1 - 5 micrograms/ml), serious adverse reactions are quite rare. The most common adverse 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 usually associated with PR and QRS interval prolongation and QT interval shortening. Lidocaine may increase ventricular rates if used in patients with atrial fibrillation. If an IV bolus is given too rapidly, 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, at very high levels, circulatory collapse. Because lidocaine is rapidly metabolized, cessation of therapy or 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 depression occur, treat with fluids, pressor agents and if necessary, begin CPR.
Drug Interactions - Lidocaine levels or effects may be increased by concomitant administration of cimetidine or propranolol. Other antiarrhythmics such as procainamide, quinidine, propranolol, phenytoin administered with lidocaine may cause additive or antagonistic cardiac effects and toxicity may be enhanced. 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).
a) Initially IV bolus of 1 - 1.5 mg/kg. Will generally distinguish between ventricular tachyarrhythmias (effective) and supraventricular tachyarrhythmias (no effect). To maintain effect, a constant IV infusion will be required. (Hilwig 1987)
a) Local anesthesia with infiltration is rarely attempted in elephants because of the difficulty in administration and the large volumes required. Moreover, local anesthesia does not aid in controlling the animals. (Nayar et.al. 2002).
b) Lidocaine blocks were used in addition to sedation with azaperone but the number of procedures performed and the doses used are not specified (Ramsey, 2000).
c) To facilitate a vaginal vestibulotomy in an Asian elephant, local anesthesia was administered with 5 injections of 20 ml lidocaine 2% + noradrenaline intra- and subcutaneously in the midline of the perineum, starting 5 cm ventrally of the anus, with an interval of 10 cm. The cow had been previously sedated with zuclopentixol (Schaftenaar, 1996).
d) In one African elephant under general anesthesia, paroxysmal ventricular tachycardia was detected and the procedure terminated when the arrhythmia failed to stabilize after multiple doses of lidocaine (1 mg/kg, IV).
a) Nayar,K.N.M., Chandrasekharan,K., and Radhakrishnan,K. 2002. Management of surgical affections in captive elephants. Journal of Indian Veterinary Association Kerala 7:(3):55-59
Ramsay,E. 2000. Standing sedation and tranquilization in captive
African elephants (Loxodonta africana). Proc. Am. Assoc. Zoo
Vet. Pages: 111-114
d) Heard,D.J., Kollias,G.V., Webb,A.I., Jacobson,E.R., and Brock,K.A. 1988. Use of halothane to maintain anesthesia induced with etorphine in juvenile African elephants. Journal of the American Veterinary Medical Association 193:254-256 Excerpts: Sixteen 3- to 5-year-old African elephants were anesthetized one or more times for a total of 27 diagnostic and surgical procedures. Xylazine (0.1 ± 0.04 mg/kg of body weight, mean ± SD) and ketamine (0.6 ± 0.13 mg/kg) administered IM induced good chemical restraint in standing juvenile elephants during a 45-minute transport period before administration of general anesthesia. After IM or IV administration of etorphine (1.9 ± 0.56 micrograms/kg), the mean time to lateral recumbency was 20 ± 6.6 and 3 ± 0.0 minutes, respectively. The mean heart rate, systolic blood pressure, and respiration rate during all procedures was 50 ± 12 beats/min, 106 ± 19 mm of Hg, and 10 ± 3 breaths/min, respectively.
Cardiac arrhythmias were detected during 2 procedures. In one elephant paroxysmal ventricular tachycardia was detected and the procedure terminated when the arrhythmia failed to stabilize after multiple doses of lidocaine (1 mg/kg, IV). In another elephant, second degree atrioventricular block returned to normal sinus rhythm after IV administration of atropine (0.04 mg/kg).
In one elephant, low mean blood pressure (54 mm of Hg) responded to reduction in halothane (vaporizer setting 1 to 0.75%) and slow infusion of dobutamine HCl ((250 mg/1,000 ml) given to effect. The systolic blood pressure increased to 90 mm of Hg and remained high with a continuous infusion of dobutamine (5 µg/kg/min).
Immediately after induction in another elephant, profound respiratory depression (< 1 breath /minute) and palpably weak arterial pulse were identified. Intravenous administration of diprenorphine at half the recommended reversal dose resulted in improvement of respiration and palpable arterial pulse, without the elephant developing signs of complete anesthetic reversal.
Alterations in systolic blood pressure, ear flapping, and trunk muscle tone were useful for monitoring depth of anesthesia. Results indicated that halothane in oxygen was effective for maintenance of surgical anesthesia in juvenile African elephants after induction with etorphine. Note: A correction appeared in a later volume 193(6): p.721.
Monitoring Parameters -
2) Symptoms of toxicity (see Adverse Effects and Overdosage)
3) If available and indicated, serum levels may be monitored. Therapeutic levels are considered to range from 1 - 6 micrograms/ml.
Client Information - This drug should only be used by professionals familiar with its use and in a setting where adequate patient monitoring can be performed.
Dosage Forms/Preparations/FDA Approval Status/Withholding Times -Lidocaine is approved for use in veterinary medicine (dogs, cats, horses, and cattle) as an injectable anesthetic, but it is not approved for use as an antiarrhythmic agent. Information regarding its use in food-producing species is conflicting. It is a prescription (Rx) drug.
Lidocaine HCl for Injection
1% (10 mg/ml) in 5 ml (50mg) and 10 ml (100 mg) syringes
2% (20 mg/ml) in 5 ml single use vials and syringes (preservative free)
2% (20 mg/ml) in 100 ml multi-use vials; Veterinary (contains preservatives)
To prepare IV infusion solution using the veterinary 2% solution add 1 gram (50 ml of 2% solution to 1 liter of D5W or other compatible solution, this will give an approximate concentration of 1 mg/ml (1000 micrograms/ml). When using a mini-drip (60 drops/ml) IV set, each drop will contain approximately 17 micrograms. In small dogs and cats, a less concentrated solution may be used for greater dosage accuracy. When preparing solution be certain that you are not using the lidocaine product that also contains epinephrine.
Lidocaine (human approved) is also available in 4%, 10%, and 20% preservative free solutions for IV admixture, for direct IM administration, and premixed with D5W for IV infusion in concentrations of 2 mg/ml, 4 mg/ml, and 5 mg/ml.
Also known as lignocaine HCl . A common trade name is Xylocaine® (Astra).
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