Lidocaine as a Numbing Agent
Lidocaine is an effective numbing agent that is widely used for local anesthesia in various clinical settings, with established efficacy for pain relief through multiple mechanisms of action. 1, 2
Mechanisms and Efficacy
- Lidocaine provides effective local anesthesia by blocking nerve conduction, with additional mechanisms including suppression of bradykinin receptor activity in sensory neurons, contributing to its analgesic effects 3
- As a topical analgesic, lidocaine penetrates the skin to produce an analgesic effect without causing complete sensory block, making it suitable for various pain conditions 4
- When applied to oral mucosa, lidocaine spray reaches maximal hypoalgesic effect after 4-5 minutes, with effects lasting up to 14 minutes, providing an optimal window for performing painful procedures 5
- In ophthalmic applications, a single application of lidocaine 2% gel has been shown to be as effective as tetracaine drops for providing corneal anesthesia during cataract surgery 6
Clinical Applications
- Lidocaine is commonly used as a local analgesic prior to painful procedures in the oral cavity and upper airways 5
- For intrauterine device placement, topical anesthetics including lidocaine can be applied to the cervix to reduce pain associated with tenaculum placement 1
- Intravenous lidocaine can be used for management of refractory cancer pain, with one phase 2 randomized study showing better pain relief compared to placebo 1
- Systemic lidocaine improves postoperative quality of recovery in patients undergoing outpatient laparoscopic surgery, with reduced opioid consumption and faster hospital discharge 7
Administration and Dosing
- For topical application, 4% lidocaine cream is used for temporarily relieving minor pain 2
- For intravenous administration in cancer pain management, lidocaine may be started as a bolus infusion of 1-3 mg/kg over 20-30 minutes, followed by a continuous infusion of 0.5-2 mg/kg/hr (maximum 100 mg/hour) if the initial dose is tolerated and effective 1
- For intramuscular administration of medications like meropenem, 1% lidocaine hydrochloride injection can be used for reconstitution to minimize injection site discomfort 8
- When using intravenous lidocaine, ideal body weight should be used for dose calculation, with a loading dose of no more than 1.5 mg/kg given over 10 minutes, followed by an infusion of no more than 1.5 mg/kg/hr for no longer than 24 hours 1
Safety Considerations
- Common side effects of lidocaine include perioral numbness, drowsiness, dizziness, tinnitus, and slurred speech 1
- More serious adverse effects can include central nervous system symptoms such as confusion, muscle twitching, respiratory depression, and cardiovascular effects like bradycardia and hypotension 1
- Risk factors for lidocaine toxicity include cardiac failure, cardiogenic shock, acidemia, hypoalbuminemia, or concurrent use of medications that reduce lidocaine metabolism 9
- Lidocaine should not be used at the same time as, or within the period of action of, other local anesthetic interventions to prevent toxicity 1
- The elimination of lidocaine is almost exclusively by the liver, with half-life averaging 1-2 hours in normal subjects but increasing to >4 hours in patients with myocardial infarction and >20 hours in those with cardiac failure 1
Precautions and Contraindications
- Lidocaine is contraindicated in patients with complete heart block or known hypersensitivity to amide-type local anesthetics 8
- Caution should be exercised when using lidocaine in patients with hepatic or renal impairment, as clearance may be affected 8
- For patients >70 years of age, those with congestive heart failure, cardiogenic shock, hepatic dysfunction, severe renal dysfunction, or preexisting neurologic dysfunction, reduced infusion rates are recommended 1
- Excessive dosage exceeding recommended limits (maximum dose with epinephrine: 7 mg/kg; without epinephrine: 4-4.4 mg/kg) increases the risk of lidocaine-induced seizures 9