Can Amitriptyline Replace Nortriptyline for Post-Herpetic Neuralgia in an Elderly Patient?
Yes, amitriptyline can be used as an alternative to nortriptyline for post-herpetic neuralgia, but nortriptyline is strongly preferred due to superior tolerability with equivalent analgesic efficacy, particularly in elderly patients who are at higher risk for anticholinergic side effects. 1, 2
Evidence Supporting Both Tricyclic Antidepressants
Both amitriptyline and nortriptyline demonstrate excellent efficacy for post-herpetic neuralgia with a number needed to treat (NNT) of 2.64, making them among the most effective treatments available 1, 2
A randomized, double-blind crossover trial of 31 patients found no difference in pain relief between amitriptyline and nortriptyline for steady pain, brief pain, or skin pain, with 67.7% of patients achieving at least a good response to one or both medications 3
Both medications provide analgesia independent of their antidepressant effects, as most responding patients showed pain relief without changes in depression ratings 3, 4
Critical Tolerability Differences in Elderly Patients
The FDA label explicitly warns that elderly patients are particularly sensitive to anticholinergic side effects of amitriptyline, including cognitive impairment, psychomotor slowing, confusion, sedation, delirium, tachycardia, urinary retention, constipation, dry mouth, blurred vision, and exacerbation of narrow-angle glaucoma. 5
Intolerable side effects were significantly more common with amitriptyline compared to nortriptyline in the head-to-head trial 3
Elderly patients taking amitriptyline are at increased risk for falls due to orthostatic hypotension, sedation, and cognitive effects 5
The FDA specifically recommends starting elderly patients on low doses of amitriptyline with close observation 5
Practical Dosing Algorithm if Amitriptyline Must Be Used
If insurance constraints require amitriptyline use in this elderly patient, start at 10 mg at bedtime (lower than standard starting doses) and increase by 10 mg every 7 days as tolerated, targeting 25-75 mg at bedtime rather than the standard 75-150 mg range. 5, 6
Monitor closely for anticholinergic side effects at each dose increase, particularly cognitive impairment, urinary retention, constipation, and orthostatic hypotension 5
The bedtime dosing schedule helps address the patient's sleep disturbance while minimizing daytime sedation 2
For depression management, the analgesic effects typically occur at lower doses and with shorter time to onset than antidepressant effects 7
Important Safety Considerations
Screen for contraindications including narrow-angle glaucoma, urinary retention, recent myocardial infarction, and concurrent use of MAO inhibitors 5
Be cautious with concurrent medications that inhibit cytochrome P450 2D6 (SSRIs, cimetidine, many antipsychotics), as these may require dose reductions of amitriptyline 5
Monitor for drug interactions with anticholinergic agents, which can cause hyperpyrexia and paralytic ileus when combined with tricyclics 5
Alternative Strategies to Consider
Appeal the insurance denial for nortriptyline by documenting that it is the preferred agent for elderly patients per clinical guidelines, emphasizing the reduced side effect burden and lower fall risk. 1, 2
Consider topical lidocaine 5% patches as first-line therapy instead, which provide excellent efficacy (NNT = 2) with minimal systemic absorption and are particularly suitable for elderly patients 1
Gabapentin remains a guideline-recommended first-line option with different side effect profile, though it also causes sedation and dizziness in elderly patients 1