Purpose of Splitting the Dose of Strattera (Atomoxetine)
The primary purpose of splitting the daily dose of Strattera into two equal doses (morning and evening) is to reduce adverse gastrointestinal effects, particularly nausea, vomiting, and abdominal pain. 1
Mechanism and Rationale
Splitting the dose improves tolerability by:
- Reducing peak plasma concentrations that occur with single daily dosing, which are associated with higher rates of GI side effects
- Distributing drug exposure more evenly throughout the day, minimizing the intensity of side effects while maintaining therapeutic coverage
The evidence explicitly states: "In order to reduce adverse effects, the daily dose of atomoxetine can be split into two equal doses administered in the morning and evening" 1. This dosing strategy was employed in multiple clinical trials, including Study 1 (N=297) where atomoxetine was "administered as a divided dose in the early morning and late afternoon/early evening" 2.
Clinical Application
When to consider split dosing:
- Patients experiencing significant GI symptoms (nausea, vomiting, abdominal pain) on once-daily dosing
- When rapid dose titration is necessary but poorly tolerated
- In the 7% of patients who are poor CYP2D6 metabolizers with higher plasma levels and longer half-lives 1
Important caveat: One study found that switching from once-daily to twice-daily dosing at midpoint was associated with improved control of oppositional defiant disorder (ODD) symptoms at home but showed no change in school functioning or ADHD symptom control 3. Interestingly, the same study found that twice-daily dosing was associated with decreased rates of stomachaches but more persistent appetite loss compared to once-daily dosing 3.
Alternative Dosing Option
If needed, atomoxetine can also be administered as a single evening dose 1. This approach may be particularly useful for patients who experience initial somnolence as a side effect, allowing this adverse effect to occur during sleep hours.
Efficacy Considerations
Both once-daily and twice-daily dosing are effective. Study 2 (N=171) specifically demonstrated that "STRATTERA is effective when administered once daily in the morning" 2. The choice between dosing schedules should be driven primarily by tolerability concerns rather than efficacy, as atomoxetine provides "around-the-clock" effects regardless of whether the total daily dose is given once or split 1.