Nortriptyline Oral Solution Dosing for 25 mg Equivalent
To deliver a 25 mg dose using nortriptyline 10 mg/5 mL oral solution, administer 12.5 mL of the solution.
Calculation and Rationale
The FDA-approved nortriptyline oral solution is supplied as 10 mg per 5 mL 1. Using basic proportional calculation:
- Desired dose: 25 mg
- Available concentration: 10 mg/5 mL (or 2 mg/mL)
- Volume required: (25 mg ÷ 10 mg) × 5 mL = 12.5 mL
Administration Guidelines
Measurement and delivery:
- Use a calibrated oral syringe or dosing cup to ensure accurate measurement of 12.5 mL 1
- Do not use household spoons, as they provide inconsistent volumes and may lead to dosing errors 1
Storage and handling:
- Store at 20°–25°C (68°–77°F) with excursions permitted between 15°–30°C (59°–86°F) 1
- Protect from light and keep the container tightly closed 1
Clinical Context for Nortriptyline Dosing
Typical adult dosing:
- Initial doses typically start at 25 mg before bed, then titrate to 75 mg/day or the maximal tolerated dose 2
- Some protocols use 75–125 mg initial doses depending on weight in inpatient settings, with therapeutic drug levels often reached within the first week 3
- Target therapeutic plasma levels are generally 50–139 ng/mL, as levels above 200 ng/mL are associated with significantly poorer clinical responses 4, 5
Common pitfalls to avoid:
- Nortriptyline causes frequent adverse effects including dry mouth (64%) and dysgeusia (20%) 2
- Orthostatic hypotension is the cardiovascular side effect of major concern, though it occurs in a minority of patients 3
- Approximately one-third of patients may be unable to complete trials due to tolerability issues 6