Maximum Dosing of Viscous Lidocaine for Oral Use
For adults, the maximum single dose of viscous lidocaine 2% is 300 mg (15 mL), administered no more frequently than every 3 hours, with a maximum of 8 doses in 24 hours. 1
Adult Dosing Parameters
The FDA-approved maximum dose is based on a weight-adjusted calculation of 4.5 mg/kg (or 2 mg/lb), not to exceed an absolute maximum of 300 mg per dose. 1 This translates to:
- Single dose: 15 mL of 2% viscous lidocaine solution (300 mg) 1
- Minimum interval: 3 hours between doses 1
- Maximum daily doses: 8 doses per 24-hour period 1
- Maximum daily total: 2,400 mg (120 mL) over 24 hours 1
For application, the solution should be swished in the mouth and spit out for oral lesions, or gargled (and may be swallowed) for pharyngeal use. 1
Pediatric Dosing Parameters
Pediatric dosing requires extreme caution due to documented cases of overdose from inappropriate dosing. 1
Children Over 3 Years
- Dose calculation: Based on weight, not to exceed 4.5 mg/kg 1
- Example: A 5-year-old child weighing 50 lbs should receive no more than 75-100 mg (3.7-5 mL of 2% solution) 1
Infants and Children Under 3 Years
- Maximum volume: 1.2 mL per dose 1
- Application method: Apply with cotton-tipped applicator to immediate area only 1
- Minimum interval: 3 hours between doses 1
- Maximum daily doses: 4 doses per 12-hour period 1
- Critical restriction: Only use if the condition requires ≤1.2 mL volume 1
Critical Safety Considerations
Systemic Absorption and Toxicity Risk
Even when used topically and spit out, viscous lidocaine can achieve measurable systemic levels, though these remain well below toxic thresholds with proper dosing. 2 Research demonstrates that when 300 mg doses are swished and spit out every 3 hours for 8 consecutive doses, plasma lidocaine levels remain below 0.3 μg/mL—far below the toxic threshold. 2
However, when viscous lidocaine is swallowed (whether intentionally or inadvertently), systemic absorption increases significantly. 2 Peak plasma levels of 0.8 μg/mL for lidocaine and 1.3 μg/mL for its metabolite MEGX have been documented after the eighth swallowed dose, though these still remain below toxic levels. 2
Documented Toxicity Cases
A case report documents lidocaine toxicity in a 22-year-old using excessive amounts (240 mL/day) of viscous lidocaine for tongue ulcers, resulting in serum levels of 6.7 μg/mL. 3 Notably, toxic symptoms persisted even after serum lidocaine levels decreased below toxic thresholds, suggesting that lidocaine metabolites (MEGX and GX) may contribute to toxicity. 3
Contraindications and Precautions
Relative contraindications include: 4
- Cardiac disease or electrolyte disorders
- Seizure disorders
- Renal or hepatic impairment
- Pregnancy or breastfeeding
- Neurological disorders
Viscous lidocaine should not be used concurrently with other local anesthetic interventions. 4 Specifically:
- Do not start viscous lidocaine within 4 hours of any nerve block, fascial plane block, or infiltration 4
- Remove topical 5% lidocaine patches before using viscous lidocaine 4
Signs of Toxicity to Monitor
Early warning signs include: 4, 5
- Tingling of tongue or lips
- Tinnitus (ringing in ears)
- Metallic taste
- Circumoral numbness
- Light-headedness
Progressive toxicity manifests as: 4, 5
- Slurred speech
- Muscle twitching
- Loss of consciousness
- Respiratory arrest
- Cardiac arrhythmias
- Ventricular arrest
If any signs of toxicity appear, immediately discontinue lidocaine and provide supportive care, including airway management and lipid emulsion therapy for cardiovascular collapse. 5
Comparison to Other Routes
For context, the maximum safe dose for viscous lidocaine (4.5 mg/kg without epinephrine) 1 is consistent with general topical and infiltration guidelines. 5 When epinephrine is added to injectable lidocaine, the maximum increases to 7.0 mg/kg (up to 500 mg total) due to reduced systemic absorption from vasoconstriction. 5, 6 However, epinephrine is not added to viscous lidocaine formulations for oral use. 1