What is the recommended duration of nortriptyline (tricyclic antidepressant) prescription for the prevention of post-herpetic neuralgia after shingles?

Duration of Nortriptyline for Post-Herpetic Neuralgia Prevention

The evidence supports starting nortriptyline at the time of acute shingles diagnosis and continuing for approximately 90 days (3 months), with the option to taper after 6 weeks if the patient is pain-free, or to continue and escalate the dose if pain persists at 6 weeks. 1

Timing and Duration Strategy

Early Initiation (Prevention Phase)

• Start nortriptyline 10-25 mg at bedtime immediately upon diagnosis of acute shingles to reduce the incidence of post-herpetic neuralgia by approximately 50% 2
• The timing between rash onset and treatment initiation is critical—earlier treatment correlates very strongly with better outcomes 1
• Begin within the first 6 days of rash onset when possible 3

Assessment at 6 Weeks

• Review the patient at 6 weeks after shingles onset 1
• If pain-free at 6 weeks: Continue low-dose nortriptyline for another 4-6 weeks (total ~10-12 weeks), then taper and discontinue 1
• If pain persists at 6 weeks: Increase the dose to 50-75 mg at bedtime over 2-3 weeks and continue treatment 2, 1

Extended Treatment for Established PHN

• For patients with established post-herpetic neuralgia (pain persisting ≥3 months), continue nortriptyline indefinitely until pain relief is achieved 4
• Post-herpetic neuralgia may persist for months to years, and some patients require long-term treatment with no specified maximum duration 4
• If tricyclic antidepressants fail to provide relief within 8 weeks of adequate dosing, refer for specialist pain management 2

Dosing Algorithm

Initial Dosing

• Start at 10-25 mg at bedtime 5, 2
• Increase every 3-7 days as tolerated 5
• Target dose: 25-100 mg at bedtime 5
• Therapeutic range for established PHN: 50-75 mg 2, 1

Rationale for Nortriptyline

• Nortriptyline is preferred over amitriptyline due to superior tolerability with equivalent analgesic benefit (NNT = 2.64) 4, 6
• Common side effects include dry mouth, constipation, and sedation, which are less pronounced than with amitriptyline 5

Key Clinical Considerations

Prevention vs. Treatment

• Preventive therapy (started during acute shingles) requires shorter duration—approximately 90 days total if pain-free at 6 weeks 1
• Treatment of established PHN (pain ≥3 months after rash) may require indefinite continuation until pain resolves, as the condition can persist for months to years 4

Monitoring and Reassessment

• The probability of pain relief correlates strongly with the brevity of the interval between rash onset and antidepressant initiation 1
• Periodic reassessment is recommended, as post-herpetic neuralgia may improve over time 4
• Patients who received antiviral treatment for acute shingles achieve pain relief faster when treated with nortriptyline 1

Common Pitfalls to Avoid

• Do not wait for PHN to develop before starting treatment—pre-emptive low-dose tricyclics from the time of shingles diagnosis significantly reduces PHN incidence 2
• Do not discontinue prematurely—if pain is present at 6 weeks, the dose should be increased rather than stopped 1
• Do not use conventional analgesics or carbamazepine as primary therapy—these have little to no value for PHN 2
• In elderly patients, start with lower doses (10 mg) and titrate more slowly to minimize side effects 6