What is the treatment for allodynia?

Treatment for Allodynia

Gabapentin is the first-line treatment for allodynia, with evidence showing it provides good pain relief for 3-4 out of 10 patients achieving at least 50% pain reduction. 1 In a randomized controlled trial, gabapentin at 900mg daily resulted in 66% decreased pain and allodynia levels, compared to 33% decrease with placebo. 2

First-Line Medications

Gabapentin

• Starting dose: 600mg on day 1, then titrate every 3 days to 1800mg daily (divided in 3 doses)
• Maximum dose: 3600mg daily
• Mechanism: Binds to α2-δ subunit of voltage-gated calcium channels, inhibiting release of glutamate, norepinephrine, and substance P
• Side effects: Dizziness, somnolence, dry mouth, constipation
• Evidence strength: FDA approved for postherpetic neuralgia with strong evidence for neuropathic pain

Pregabalin

• Starting dose: 75mg at bedtime, with gradual weekly increase
• Target dose: 300-600mg daily (divided doses)
• Note: More predictable pharmacokinetics than gabapentin but similar efficacy
• Side effects: Similar to gabapentin
• Evidence strength: FDA approved for neuropathic pain 2

Topical Lidocaine

• Formulation: 5% patch or gel
• Application: Apply to affected area
• Best for: Well-localized neuropathic pain with allodynia
• Advantage: Minimal systemic effects, excellent for elderly patients
• Evidence strength: Shown efficacy in patients with allodynia due to different types of peripheral neuropathic pain 2

Second-Line Medications

Duloxetine (SNRI)

• Starting dose: 30mg daily for one week, then 60mg daily
• Maximum dose: 120mg daily
• Mechanism: Inhibits serotonin and norepinephrine reuptake
• Side effects: Nausea, dry mouth, headache, decreased libido, dizziness
• Contraindications: Severe hepatic and renal impairment
• Evidence strength: FDA approved for diabetic neuropathy 2

Tricyclic Antidepressants (TCAs)

• Options: Amitriptyline or imipramine
• Starting dose: 10mg at bedtime (especially in elderly)
• Target dose: 25-75mg daily
• Mechanism: Balanced inhibition of norepinephrine and serotonin reuptake
• Side effects: Drowsiness, anticholinergic effects
• Caution: Avoid doses >100mg/day in patients with cardiovascular disease
• Evidence strength: Number needed to treat (NNT) of 1.5-3.5 2

Third-Line Medications

Tramadol

• Starting dose: 50mg once or twice daily
• Maximum dose: 400mg daily
• Mechanism: Weak μ-opioid agonist plus norepinephrine and serotonin reuptake inhibitor
• Side effects: Nausea, vomiting, constipation, sedation
• Caution: Risk of dependence, seizures, and serotonin syndrome
• Best use: Short-term relief when immediate pain control is needed 2

Other Opioids

• Reserved for refractory cases or acute exacerbations
• Options include morphine, oxycodone
• Significant risks of addiction, dependency, and side effects
• Should be used with caution and for limited duration 1

Topical Treatments

Capsaicin

• High-concentration (8%) patches have shown efficacy in HIV-associated neuropathy
• Low-concentration (0.075%) cream applied 3-4 times daily
• Initial burning sensation common but decreases with continued use
• Mechanism: Depletes substance P from sensory nerve endings

Non-Pharmacological Approaches

Physical Interventions

• Exercise therapy focusing on strengthening and flexibility
• Weight loss for overweight patients to reduce pressure on nerves
• Avoidance of tight clothing or other mechanical irritants
• Cognitive behavioral therapy for pain management 1

Advanced Interventions

• For refractory cases: Consider spinal cord stimulation, nerve blocks
• Transcutaneous electrical nerve stimulation (TENS)
• Referral to pain specialist for interventional procedures 1

Treatment Algorithm

1. Start with gabapentin (titrate to 1800mg daily over 1-2 weeks)
2. If inadequate response after 4 weeks at maximum tolerated dose:
   • Add or switch to pregabalin OR
   • Add topical lidocaine if pain is localized
3. If still inadequate response:
   • Add duloxetine or amitriptyline (start low, titrate slowly)
4. For refractory pain:
   • Consider tramadol for short-term use
   • Consider referral to pain specialist for interventional options

Monitoring and Follow-up

• Assess pain reduction using validated scales
• Monitor for side effects, particularly sedation and dizziness
• Evaluate for improvement in function and quality of life
• Adjust medication doses based on response and tolerability

Important Considerations

• Timing of medication may affect efficacy (e.g., gabapentin's effect varies with circadian rhythms) 3
• Early treatment with anticonvulsants may prevent chronification of allodynia 4
• Topical gabapentin gel may provide localized relief without systemic side effects 5
• Combination therapy often needed for adequate pain control

The treatment of allodynia requires patience and careful titration of medications to balance efficacy and side effects. Gabapentin remains the cornerstone of therapy with strong evidence supporting its use.