What is the recommended dose of 2% intranasal lidocaine for an adult with idiopathic trigeminal or post‑herpetic facial neuralgia who has no lidocaine allergy, cardiac conduction disease, severe hepatic impairment, or concurrent class I anti‑arrhythmic use?

Intranasal Lidocaine Dosing for Trigeminal Neuralgia

For acute trigeminal neuralgia exacerbations affecting the second (V2) and/or third (V3) divisions, administer 2% intranasal lidocaine as two metered-dose sprays (0.2 mL total) into the affected nostril, which provides prompt pain relief within 15 minutes lasting approximately 4 hours.

Specific Dosing Protocol

• Administer two sprays (0.2 mL total volume) of 2% lidocaine into the nostril on the affected side 1
• The 2% concentration delivers approximately 16 mg of lidocaine per 0.2 mL dose, which is well below the maximum safe dose of 4.5 mg/kg (300 mg maximum in adults) 2
• For patients requiring higher concentrations, 8% lidocaine spray has been studied and shown effective, though 2% is the standard formulation 1, 3

Expected Clinical Response

• Pain relief typically occurs within 15 minutes of administration, with visual analog scale (VAS) scores decreasing from 8.0 cm to 1.5 cm 1
• The analgesic effect persists for an average of 4.3 hours (range 0.5-24 hours) 1
• In a larger retrospective study of 152 patients, 77.6% achieved effective pain relief at 15 minutes and 70.4% at 30 minutes when using lidocaine aerosol on oral and/or nasal mucosa 3

Anatomical Rationale

• The second division of the trigeminal nerve (V2) passes through the sphenopalatine ganglion, located posterior to the middle turbinate and covered by mucous membrane, making it accessible to intranasal application 1
• This targeted approach provides localized anesthesia without the paraesthesia associated with traditional trigeminal nerve blocks 1

Patient Selection and Predictors of Response

• V2, V3, or V2+V3 trigeminal neuralgia responds significantly better to intranasal lidocaine compared to V1 involvement 3
• Patients already taking maximum doses of carbamazepine or oxcarbazepine are less likely to experience immediate pain relief (OR 6.15), suggesting this is best used as rescue therapy in patients not yet at maximum oral medication doses 3
• This intervention is particularly valuable for acute exacerbations while awaiting definitive surgical treatment 3

Safety Considerations and Monitoring

• No serious adverse reactions were reported in the clinical trials of intranasal lidocaine for trigeminal neuralgia 1
• The dose used (16 mg from 0.2 mL of 2% solution) represents only 5% of the maximum safe dose for a 70 kg adult 2
• Do not administer within 4 hours of other local anesthetic interventions to prevent cumulative toxicity 2, 4
• Monitor for early signs of systemic toxicity including circumoral numbness, facial tingling, and metallic taste, though these are unlikely at this low dose 2

Clinical Context and Limitations

• Intranasal lidocaine provides temporary relief only and should be used as part of a comprehensive treatment strategy that includes oral anticonvulsants (carbamazepine as first-line) 5
• This approach is most appropriate for paroxysmal pain triggered by touching or moving the face 1
• The effect is prompt but temporary, making it ideal for acute exacerbations rather than chronic maintenance therapy 1
• For V1 (ophthalmic division) trigeminal neuralgia, intranasal administration is less effective due to anatomical considerations 3

Common Pitfalls to Avoid

• Calculate the dose in milligrams before administration to avoid volumetric errors—two sprays of 2% lidocaine delivers only 16 mg, far below toxic levels 2
• Do not assume this replaces definitive treatment; it is a rescue therapy for acute exacerbations 3
• Avoid using in patients with advanced liver failure, as hepatic impairment reduces lidocaine clearance by 60%, though systemic absorption from intranasal application is minimal 6