Lidocaine is a common medication classified as both a local anesthetic and a Class Ib antiarrhythmic agent. Its primary function is to block nerve signals, temporarily causing numbness or loss of feeling in a specific area of the body. It is most often used as a topical cream, transdermal patch, or injectable solution to manage pain during minor medical procedures or to stabilize certain heart rhythms. Lidocaine is formulated for application to the skin or directly into tissues, which limits the amount entering the bloodstream; it is not intended for oral consumption.
Why Ingesting Lidocaine is Dangerous
Ingesting lidocaine is highly dangerous because it bypasses the controlled absorption of topical or injected use, leading to rapid systemic uptake through the gastrointestinal tract. This sudden influx of the drug into the bloodstream quickly causes Local Anesthetic Systemic Toxicity (LAST). The concentration of lidocaine rises to toxic levels faster than the body can clear it. The liver, which metabolizes lidocaine, is overwhelmed by the sudden high dose and cannot process the drug quickly enough. Swallowing topical products, especially concentrated liquids, results in dangerously high plasma concentrations that affect the entire body.
How Ingested Lidocaine Affects the Body
Lidocaine blocks voltage-gated sodium channels, which generate and conduct electrical impulses in nerve and heart cells. When high concentrations enter the systemic circulation, the drug disrupts normal electrical signaling in the central nervous system (CNS) and the cardiovascular system.
In the CNS, the initial effect is often excitatory, causing overstimulation of brain pathways, followed by a depressive phase as the drug blocks both excitatory and inhibitory signals. In the heart, high levels directly impair cardiac conduction by interfering with sodium ion movement. This slows the heart rate, decreases the force of contraction, and can lead to severe cardiac rhythm abnormalities and a sharp drop in blood pressure.
Recognizing Signs of Systemic Toxicity
Symptoms of lidocaine systemic toxicity (LAST) typically progress rapidly, starting with the central nervous system before advancing to affect the heart. Early signs include sensory disturbances such as numbness around the mouth and tongue, a metallic taste, and ringing in the ears (tinnitus). Initial neurological symptoms also involve lightheadedness, confusion, dizziness, or slurred speech.
As lidocaine concentration rises, symptoms progress to severe manifestations like muscle twitching, tremors, and seizures. At the highest toxic levels, the CNS becomes severely depressed, leading to unconsciousness, coma, and respiratory arrest. Concurrently, cardiotoxicity manifests as a slow heart rate (bradycardia), low blood pressure (hypotension), and complex arrhythmias, which can quickly result in cardiac arrest.
Immediate Emergency Steps
If lidocaine ingestion is suspected, immediate action is necessary because systemic toxicity progresses quickly and is life-threatening. The first step is to call emergency services, such as 911, and the national Poison Control hotline. Provide responders with details including the person’s age, the type of product ingested, and the estimated amount.
Do not attempt to induce vomiting unless specifically instructed by a medical professional or Poison Control. If the person is conscious, monitor their breathing and alertness closely, as symptoms can worsen suddenly. If the individual begins seizing or loses consciousness, place them on their side to maintain an open airway while waiting for help.
Forms of Lidocaine with High Ingestion Risk
The risk of severe toxicity is highest with concentrated liquid formulations designed for topical use on mucous membranes. Viscous lidocaine solution, often prescribed to treat pain from mouth sores or throat irritation, poses a significant ingestion risk because it is easily swallowed and highly concentrated.
High-concentration sprays used for airway anesthesia can also deliver a large dose if accidentally or intentionally ingested. While lower-concentration topical creams, gels, and patches are primarily absorbed through the skin, ingesting a large quantity can still lead to systemic toxicity. Children are at an increased risk of severe toxicity and death from accidental ingestion of these concentrated forms.