Adult Dose of Viscous Lidocaine for Sore Throat
For an adult with a sore throat, use 15 mL of viscous lidocaine 2% (300 mg) swished and gargled, then either spit out or swallowed, with a minimum 3-hour interval between doses and a maximum of 8 doses in 24 hours. 1
Standard Dosing Protocol
The FDA-approved dosing for symptomatic treatment of irritated or inflamed mucous membranes is:
- Single dose: 15 mL (one tablespoonful) of undiluted 2% viscous lidocaine 1
- Maximum single dose: Must not exceed 4.5 mg/kg or 300 mg total in healthy adults 1
- Frequency: Minimum 3-hour intervals between doses 1
- Maximum daily: No more than 8 doses in 24 hours 1
Application Technique
For mouth pain: Swish the solution around in the mouth and spit out 1
For pharyngeal/throat pain: Gargle the undiluted solution and may swallow 1
Critical Safety Considerations
Maximum dose limits must be strictly observed - the 4.5 mg/kg limit without epinephrine translates to approximately 315 mg for a 70 kg adult, but the FDA label caps this at 300 mg per dose 1, 2
Avoid cumulative toxicity by not using viscous lidocaine within 4 hours of any other local anesthetic intervention (nerve blocks, topical anesthetics, dental procedures) 2, 3
Calculate total lidocaine exposure from all sources, as combining local anesthetics increases toxicity risk 2
Evidence Supporting Safety at Recommended Doses
Research demonstrates that when used as directed topically in the oral cavity (swished and spit), systemic lidocaine levels remain negligible (never exceeding 0.3 μg/mL) 4. Even when swallowed at the maximum recommended dose of 300 mg every 3 hours for 8 consecutive doses, peak plasma levels only reached 0.8 μg/mL after the eighth dose - well below toxic concentrations 4.
However, excessive use carries real toxicity risk - a case report documented lidocaine toxicity when a patient used 240 mL per day (far exceeding recommended dosing), achieving a serum level of 6.7 μg/mL 5.
Warning Signs of Toxicity
Discontinue immediately and seek emergency care if any of these symptoms develop:
- Circumoral numbness or facial tingling 2
- Slurred speech or metallic taste 2
- Tinnitus or auditory disturbances 2
- Light-headedness or confusion 2
- Muscle twitching 2
Severe toxicity (at plasma concentrations >10 μg/mL) can progress to loss of consciousness, respiratory arrest, cardiac arrhythmias, and ventricular arrest 2
High-Risk Populations Requiring Dose Reduction
Use lower doses or avoid in:
- Patients with advanced liver failure (decreased lidocaine clearance) 2
- Body weight <40 kg 2
- Age >70 years 2
- Renal dysfunction 2
- Pre-existing cardiac, neurologic, or seizure disorders 2
For these patients, consider starting with 10 mL doses instead of 15 mL, or extending the interval to 4-6 hours between doses 1.
Alternative Considerations
While the UK guidelines for Stevens-Johnson syndrome mention viscous lidocaine 2% at 15 mL per application as an alternative to benzydamine for severe oral discomfort 6, this same dosing applies to routine sore throat management. The guidelines note this should be used when pain is inadequately controlled with first-line anti-inflammatory rinses 6.
Important caveat: The evidence for lidocaine lozenges in sore throat shows mixed results - higher doses (8 mg lidocaine lozenges) were not superior to lower doses (1 mg) in clinical trials 7, suggesting that for oral mucosal contact, the concentration and contact time matter more than total dose.