Lidocaine

Lidocaine is an amide local anesthetic and a class IB antiarrhythmic. US products include Xylocaine and generic injections (infiltration, nerve block, epidural and intravenous antiarrhythmic use) and many topical forms: 5% ointment, 4% solution, 2% jelly, 2% viscous oral solution, Lidoderm 5% patch, ZTlido 1.8% patch, and combinations such as EMLA (lidocaine/prilocaine) and Pliaglis (lidocaine/tetracaine). Lake Hills Pharmacy uses lidocaine in compounded topical anesthetic preparations.

• Injection: local or regional anesthesia by infiltration, peripheral nerve block and epidural techniques; intravenous treatment of ventricular arrhythmias.
• Lidoderm and ZTlido patches: relief of pain associated with postherpetic neuralgia.
• Topical ointment, solution and jelly: anesthesia of accessible mucous membranes and of the urethra, and relief of pain from minor burns and skin irritation.
• EMLA and Pliaglis: dermal anesthesia or analgesia on intact skin before superficial procedures.
• Prescribers use lidocaine in compounded topical anesthetic creams for procedural skin anesthesia and for localized pain.

Lidocaine blocks voltage-gated sodium channels, binding preferentially to the inactivated state, which stabilizes neuronal membranes and blocks initiation and conduction of nerve impulses. In the heart it shortens the action potential duration in Purkinje fibers and suppresses ventricular automaticity.

Systemic absorption depends on dose, site, area treated, contact time, skin integrity, vascularity, heat and occlusion; it is low through intact skin and high through mucous membranes. Lidocaine is 60 to 80% protein bound, mainly to alpha-1-acid glycoprotein. It is metabolized in the liver by CYP1A2 and CYP3A4 to the active metabolites monoethylglycinexylidide and glycinexylidide; less than 10% is excreted unchanged. The half-life is about 1.5 to 2 hours and is prolonged in hepatic impairment and heart failure.

• Hypersensitivity to lidocaine, other amide-type local anesthetics or any component.
• Intravenous antiarrhythmic use: Stokes-Adams syndrome, Wolff-Parkinson-White syndrome, and severe sinoatrial, atrioventricular or intraventricular block without a pacemaker.

• Methemoglobinemia: reported with local anesthetics; risk is higher with G6PD deficiency, congenital methemoglobinemia, cardiac or pulmonary compromise, infants under 6 months, and concurrent oxidizing drugs.
• Systemic toxicity: CNS effects (lightheadedness, perioral numbness, tinnitus, confusion, tremor, seizures, respiratory depression) and cardiovascular effects (bradycardia, hypotension, arrhythmia, cardiac arrest).
• Topical use over large areas, for long periods, on broken skin, with heat or under occlusion increases absorption; FDA has warned of seizures and deaths with compounded topical anesthetics used this way.
• Use caution in hepatic impairment, heart failure, debilitated or elderly patients, and in patients with conduction disorders. Avoid the eyes.

• Class I antiarrhythmics (such as mexiletine) and other local anesthetics: additive toxicity.
• CYP1A2 inhibitors (fluvoxamine, ciprofloxacin), CYP3A4 inhibitors (erythromycin, itraconazole), amiodarone, cimetidine and beta-blockers such as propranolol: raise lidocaine levels.
• Methemoglobin-inducing drugs (dapsone, nitrates and nitrites, sulfonamides, primaquine, nitrofurantoin): increased methemoglobinemia risk.
• Class III antiarrhythmics such as amiodarone: additive cardiac effects.

Topical: erythema, edema, blanching, burning, itching and contact dermatitis. Systemic: dizziness, drowsiness, paresthesia, tinnitus, blurred vision, tremor, seizures, bradycardia, hypotension, arrhythmia and, rarely, methemoglobinemia or anaphylaxis.

Lidocaine crosses the placenta and has been used widely in obstetric anesthesia without evidence of teratogenicity at clinical exposures. Small amounts pass into breast milk and are poorly absorbed orally by the infant, so topical use during breastfeeding is generally considered compatible.

With high-strength or large-area topical use: early signs of systemic toxicity (perioral numbness, tinnitus, dizziness, confusion, arrhythmia), pulse oximetry and co-oximetry if methemoglobinemia is suspected, and adherence to the prescribed amount, area and time. With intravenous use: ECG, blood pressure and CNS status.

• Xylocaine (lidocaine HCl) Injection Prescribing Information, Fresenius Kabi.
• Lidoderm (lidocaine patch 5%) Prescribing Information.
• Lidocaine Hydrochloride Oral Topical Solution USP 2% (viscous) prescribing information.
• FDA Drug Safety Communication: risk of methemoglobinemia with benzocaine and other local anesthetics (2018).
• FDA Public Health Advisory: life-threatening side effects with skin numbing products used for cosmetic procedures (2009).