Drugs & Medication

Lidocaine
Systematic (IUPAC) name
2-(diethylamino)- N-(2,6-dimethylphenyl)acetamide
Identifiers
CAS number	137-58-6
ATC code	N01BB02 C01BB01
PubChem	3676
DrugBank	APRD00479
Chemical data
Formula	C14H22N2O
Mol. weight	234.34 g/mol
Physical data
Melt. point	68 °C (154 °F)
Pharmacokinetic data
Bioavailability	35% (oral) 3% (topical)
Metabolism	hepatic 90% (CYP1A2)
Half life	1.5–2 hours
Excretion	renal
Therapeutic considerations
Pregnancy cat.	A (Australia)
Legal status	Schedule 4 (Australia)
Routes	IV, subcutaneous, topical

Lidocaine (INN) (IPA: [ˈlaɪdokeɪn]) or lignocaine (former BAN) (IPA: [ˈlɪgnokeɪn]) is a common local anesthetic and antiarrhythmic drug. The most commonly encountered lidocaine preparations are marketed by AstraZeneca under the brand names Xylocaine and Xylocard, though lidocaine is also found in many other proprietary preparations.

Contents 1 History 2 Pharmacokinetics 3 Pharmacology 3.1 Anesthesia 3.2 Antiarrhythmia 4 Clinical use 4.1 Indications 4.2 Contraindications 4.3 Adverse drug reactions 4.4 Dosage forms 5 References

History

Lidocaine, the first amino amide-type local anesthetic, was developed by Nils Löfgren and Bengt Lundqvist in 1943 and first marketed in 1948.

Pharmacokinetics

Lidocaine has a more rapid onset of action and longer duration of action than amino ester-type local anesthetics such as procaine. It is approximately 90% metabolized in the liver by CYP1A2 (and to a minor extent CYP3A4) to the pharmacologically-active metabolites monoethylglycinexylidide and glycinexylidide.

The elimination half-life of lidocaine is approximately 1.5–2 hours in most patients. This may be prolonged in patients with hepatic impairment (average 343 minutes) or congestive heart failure (average 136 minutes). (Thomson et al., 1973)

Pharmacology

Anesthesia

Lidocaine alters depolarization in neurons, by blocking the fast sodium (Na⁺) channels in the cell membrane. With sufficient blockade, the membrane will not depolarise and so not transmit an action potential, leading to its anesthetic effects.

Antiarrhythmia

Lidocaine is classified as a Class Ib antiarrhythmic agent, blocking the sodium channel of the cardiac action potential, which decreases automaticity by reducing the slope of phase 0 of depolarization with little effect on the PR interval, QRS complex or QT interval.

Clinical use

Indications

Indications for the use of lidocaine include:

• Topical, infiltration, nerve block, ophthalmic, epidural and intrathecal anaesthesia, IV regional anaesthesia (IVRA)
• Treatment of serious ventricular arrhythmias (IV preparations), including VF (Ventricular Fibrillation) associated with cardiac arrest
• Neuropathic pain, including postherpetic neuralgia

Contraindications

Contraindications for the use of lidocaine include:

• Heart block, second or third degree (without pacemaker)
  Severe sinoatrial block (without pacemaker)
  Serious adverse drug reaction to lignocaine or amide local anaesthetics
  Concurrent treatment with quinidine, flecainide, disopyramide, procainamide (Class I antiarrhythmic agents)

Adverse drug reactions

Adverse drug reactions (ADRs) are rare when lidocaine is used as a local anesthetic and is administered correctly. Most ADRs associated with lidocaine for anesthesia relate to administration technique (resulting in systemic exposure) or pharmacological effects of anesthesia, however allergic reactions can rarely occur.

Systemic exposure to excessive quantities of lidocaine mainly result in central nervous system (CNS) and cardiovascular effects – CNS effects usually occur at lower plasma concentrations and additional cardiovascular effects present at higher concentrations, though cardiovascular collapse may also occur with low concentrations. CNS effects may include CNS excitation (nervousness, tingling around the mouth, tinnitus, tremor, dizziness, blurred vision, seizures) followed by depression (drowsiness, loss of consciousness, respiratory depression and apnea). Cardiovascular effects include hypotension, bradycardia, arrhythmias, and/or cardiac arrest – some of which may be due to hypoxemia secondary to respiratory depression. (Rossi, 2006)

ADRs associated with the use of intravenous lidocaine are similar to toxic effects from systemic exposure above. These are dose-related and more frequent at high infusion rates (≥3 mg/minute). Common ADRs include: headache, dizziness, drowsiness, confusion, visual disturbances, tinnitus, tremor, and/or paraesthesia. Infrequent ADRs assocaited with the use of lidocaine include: hypotension, bradycardia, arrhythmias, cardiac arrest, muscle twitching, seizures, coma, and/or respiratory depression. (Rossi, 2006)

Dosage forms

Lidocaine, usually in the form of lidocaine hydrochloride, is available in various forms including:

• Injected local anesthetic (sometimes combined with epinephrine)
• Dermal patch (sometimes combined with prilocaine)
• Intravenous injection (sometimes combined with epinephrine)
• Intravenous infusion
• Nasal instillation/spray (combined with phenylephrine)
• Oral gel (often referred to as "viscous lidocaine" or abbreviated "lidocaine visc" or "lidocaine hcl visc" in pharmacology)
• Oral liquid
• Topical gel (as with Aloe Vera gels that include Lidocaine)
• Topical liquid

References

• Rossi S, editor. Australian Medicines Handbook 2006. Adelaide: Australian Medicines Handbook; 2006. ISBN 0-9757919-2-3
• Thomson PD, Melmon KL, Richardson JA, et al. Lidocaine pharmacokinetics in advanced heart failure, liver disease, and renal failure in humans. Ann Intern Med 1973;78(4):499-508. PMID 4694036