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Lidocaine: Pharmacodynamics, Pharmacokinetics & Pharmacology

Instructor: Charity Hacker

I am a nursing instructor with over 20 years of nursing experience and a Masters Degree in Nursing Education.

Most people know that lidocaine is used to numb things, but there is so much more to know about this drug. In this lesson, we will explore the pharmacology, pharmacodynamics, and pharmacokinetics of the popular medication, lidocaine.

Lidocaine: It's for More Than Just Numbing

Imagine you're working in a hospital and one of the patients on a cardiac unit becomes unresponsive. An alarm sounds, a code is called, and many professionals come to the bedside of the patient, who is experiencing cardiac arrest. In other words, your patient is having a heart attack and is unresponsive. You hear someone yell for lidocaine. But you thought lidocaine was just for numbing things?

Lidocaine is a medication that most people know as an anesthetic, but it's actually also an antiarrhythmia agent. In this lesson, we'll explore what you need to know about lidocaine before administering it, and learn some details about its pharmacodynamics and pharmacokinetics.

Lidocaine for treatment of cardiac arrhythmias.
Picture of 2% lidocaine for treatment of cardiac arrhythmias.

Getting to Know Lidocaine

Lidocaine, trademark name Xylocaine, is an amide-type anesthetic most frequently used for anesthesia, or numbing. As a cardiac antiarrhythmic agent, lydocaine is typically used in emergency scenarios to treat ventricular arrhythmias.

When used in Advanced Cardiac Life Support (ACLS) and Pediatric Advanced Life Support (PALS), lydocaine's specific indications include:

  • monographic ventricular tachycardia (VT)
  • polymorphic VT
  • otherwise unresponsive pulseless VT or ventricular fibrillation (VF) (as an alternate for amiodorone)

Lidocaine may also be used in some instances to treat cardiac emergencies related to elevated blood pressure greater than 180/120, or acute coronary syndrome related to overdoses.

Use with Caution

In emergency cases of life and death, potential side-effects are often the least of your concerns, but it's still absolutely necessary to be aware of adverse effects and specific population concerns.

Special Populations

The following special populations have an increased risk of lidocaine toxicity:

  • Those suffering from hepatic dysfunction (liver failure)
  • People with pseudocholinesterase deficiency
  • Geriatrics (decreased clearance, increased half-life)
  • Infants & young children (when dosing guidelines not followed)

Other patients to whom you should be very careful administering lydocaine include:

  • Pregnant women: the benefits must outweigh unknown risk to fetus
  • Breast-feeding women: use with caution
  • Those with a known allergy to amide-type local anesthetics
  • Patients taking monoamine oxidase (MAO) inhibitors or tricyclic antidepressants
  • Patients with heart failure (HF) or recent myocardial infarction (heart attack) (MI)

Potential Adverse Effects

That's quite a few people to worry about, but there are also possible side effects for people who don't fit into those categories, including:

  • Allergic reaction
  • Cardiac: bradycardia and hypotension progressing to circulatory shock and arrhythmias
  • Gastrointestinal: nausea and vomiting
  • Neurological: headache, shivering, and spinal/nerve pain are the most common, with agitation, anxiety, and psychosis progressing to confusion and loss of consciousness to the more lethal end results noted below
  • Respiratory: shortness of air and bronchospasm
  • Potentially lethal: arrhythmia, respiratory depression, seizure, coma, and death

When lidocaine is being administered intravenously (IV), you should always have emergency CPR (cardiopulmonary resuscitation) equipment available and the patient should have a continuous ECG (electrocardiogram) monitor attached.

Pharmacodynamics of Lidocaine

Lidocaine is classified as a voltage-gated sodium channel blocker, and that's exactly how it performs its desired action. Lidocaine prohibits the activation of nerve channels (sodium channels) that rely on electromagnetic currents (voltage). Nerve cells fire repeatedly to pass on signals of pain or stimulation, but to do this they must polarize and repolarize. Lidocaine blocks this process.

Voltage-gated sodium channel blockers open and closed.
Picture showing how voltage-gated sodium channel blockers look open and closed.

Lidocaine Movements

Let's go back to the hospital - the code has ended and the patient survived. But what was happening to the lidocaine after it entered the patient's body? This is called pharmacokinetics, and is best divided into categories: absorption, distribution, metabolism, and elimination. Since lidocaine has so many routes, uses, and prescribed doses, its pharmacokinetics are often dose and route dependent.

Absorption of Lidocaine

When lidocaine is given by IV, it's nearly 100% absorbed and acts very quickly, within 45-90 seconds. This is why IV is the route of choice in emergency situations. Lidocaine is otherwise absorbed by the gastrointestinal tract. When it enters the body this way it passes through the liver, limiting the amount of unchanged medication that makes it to its destination to roughly 35%. This demonstrates how the route of administration can affect the bioavailability of a medication like lidocaine.

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