Dose Equivalence: 50mg Doxepin to Amitriptyline
Based on the highest quality evidence available, 50mg of doxepin is approximately equivalent to 43.6mg of amitriptyline 1.
Evidence-Based Conversion
The most rigorous data comes from a 2015 systematic analysis of 83 randomized controlled trials involving 14,131 participants that calculated dose equivalents using weighted mean ratios from flexible-dose comparative studies 1. This study established that:
- Doxepin 140.1mg/day is equivalent to fluoxetine 40mg/day
- Amitriptyline 122.3mg/day is equivalent to fluoxetine 40mg/day
Using these ratios as reference points:
- 50mg doxepin = (50/140.1) × 122.3 = approximately 43.6mg amitriptyline
Clinical Context from Guidelines
Multiple guidelines list both medications as tricyclic antidepressants with similar mechanisms and therapeutic applications 2, 3, 4. They are used interchangeably for:
- Neuropathic pain (goal dosing typically 75-150mg for either agent) 5, 2
- Depression prophylaxis in cyclic vomiting syndrome 2
- Painful diabetic peripheral neuropathy (amitriptyline 25-75mg/day range) 4
Important Clinical Considerations
Anticholinergic burden differs: Amitriptyline has more anticholinergic and antihistaminergic activity than doxepin 5, 2. This means that even at equivalent analgesic doses, patients may experience more:
- Dry mouth
- Sedation
- Urinary retention
- Constipation
- Blurred vision
Starting doses are typically lower than conversion suggests: FDA labeling indicates amitriptyline typically starts at 25-50mg for outpatients 6, while clinical practice often uses 10-25mg initially 4, 7. The conversion ratio applies to established therapeutic doses, not necessarily starting doses.
Cardiac monitoring applies equally: Both agents carry similar cardiovascular risks, with caution advised for doses >100mg/day due to increased sudden cardiac death risk 4. ECG screening is recommended for patients over 40 years or those with cardiac history 4.