What is the appropriate dose of viscous lidocaine (lidocaine) for an adult with viral laryngitis?

Viscous Lidocaine Dosing for Adult Viral Laryngitis

For an adult with viral laryngitis, use 15 mL (one tablespoonful) of 2% viscous lidocaine, gargled and swallowed, with a maximum of 300 mg total dose per administration, repeated no more frequently than every 3 hours, and not exceeding 8 doses in 24 hours. 1

Standard Adult Dosing Protocol

• The FDA-approved dose is 15 mL of 2% viscous lidocaine (300 mg) as a single dose for pharyngeal symptoms 1
• For pharyngeal use specifically (as in laryngitis), the undiluted solution should be gargled and may be swallowed 1
• The maximum single dose must not exceed 4.5 mg/kg or 2 mg/lb body weight, with an absolute maximum of 300 mg per dose regardless of body weight 1

Critical Timing and Frequency Restrictions

• Minimum interval between doses is 3 hours 1
• Maximum of 8 doses in any 24-hour period 1
• These restrictions are essential to prevent systemic toxicity, as lidocaine has a narrow therapeutic window with toxicity beginning at plasma levels only slightly above therapeutic concentrations 2

Important Safety Considerations

Toxicity Risk Factors

• Early warning signs of lidocaine toxicity occur at plasma concentrations of 5-10 μg/mL and include circumoral numbness, facial tingling, slurred speech, tinnitus, light-headedness, and dizziness 2
• Severe toxicity at concentrations above 10 μg/mL includes muscle twitching, loss of consciousness, respiratory arrest, and cardiac arrhythmias 2
• Toxicity can occur even with recommended dosing if used too frequently, as demonstrated in a case report where symptoms developed with 240 mL per day use (serum level 6.7 μg/mL) 3

High-Risk Populations Requiring Dose Reduction

• Patients with hepatic impairment or advanced liver failure (decreased lidocaine clearance) 2
• Patients with renal dysfunction 2
• Elderly patients over 70 years 2
• Patients weighing less than 40 kg 2
• Those with cardiac disease, seizure disorders, or neurological conditions 2

Clinical Context: Viral Laryngitis

• Antibiotics are not effective for viral laryngitis - they do not improve objective voice scores and provide only modest subjective benefits that do not outweigh risks 4
• Viscous lidocaine provides symptomatic relief only; it does not treat the underlying viral infection 1
• The primary symptom requiring treatment in laryngitis is dysphonia (in chronic cases) or dyspnea (in acute cases), though dyspnea is more common in children 5

Critical Warnings

• Never combine viscous lidocaine with other local anesthetic preparations without accounting for cumulative dose - this includes topical patches, creams, or injectable forms 2
• Do not use within 4 hours of any other local anesthetic intervention 2
• If any signs of toxicity appear (circumoral numbness, tingling, confusion, slurred speech), discontinue immediately and seek emergency medical attention 2
• Have resuscitation equipment and 20% lipid emulsion available in settings where higher doses or repeated administration may occur 2

Common Pitfall to Avoid

The most dangerous error is prescribing viscous lidocaine on a "PRN" (as needed) basis without specific dosing instructions, as this significantly increases overdose risk 6. Always provide explicit instructions on amount, frequency, maximum daily dose, and minimum time intervals between doses 6.