About This Calculator
The Strattera Dose Calculator provides dosing recommendations for atomoxetine based on current prescribing guidelines for the treatment of Attention-Deficit/Hyperactivity Disorder (ADHD). It considers critical patient factors including age, weight, hepatic function, and concurrent use of strong CYP2D6 inhibitors to suggest an appropriate dosing schedule. This tool is intended for educational purposes for healthcare professionals.
Outputs Explained
After entering the patient’s information, the calculator will provide the following outputs, which are essential for creating a safe and effective atomoxetine dosing schedule:
- Initial Daily Dose: The recommended starting dose for the first several days of treatment to assess tolerability.
- Recommended Target Dose: The standard therapeutic dose to aim for after the initial titration period. Clinical efficacy is typically assessed at this dose level.
- Maximum Recommended Dose: The highest daily dose that should be administered, not to be exceeded.
Each output includes the precise calculation (e.g., 35.4 mg) and a practical dose rounded to the nearest available Strattera® capsule strength (10, 18, 25, 40, 60, 80, or 100 mg).
How to Use the Calculator
To ensure accurate dosing recommendations, input the following patient data:
- Patient Age: Enter the patient’s age in years. The calculator is validated for patients aged 6 and older, consistent with prescribing guidelines.
- Patient Weight: Provide the patient’s body weight. You can enter the value in either kilograms (kg) or pounds (lbs).
- Hepatic Impairment: Select the patient’s level of liver function. This is critical as atomoxetine is extensively metabolized by the liver. Choose from Normal, Moderate (Child-Pugh Class B), or Severe (Child-Pugh Class C).
- Strong CYP2D6 Inhibitor: Check this box if the patient is taking a potent inhibitor of the CYP2D6 enzyme, such as paroxetine, fluoxetine, or quinidine. This can significantly increase atomoxetine concentrations.
Dosing Overview
Children & Adolescents (≤ 70 kg)
Dosing is weight-based for this population.
- Initiation: Start at a total daily dose of approximately 0.5 mg/kg.
- Titration: Maintain the initial dose for at least 3 days before increasing.
- Target Dose: The recommended target dose is approximately 1.2 mg/kg/day.
- Maximum Dose: Do not exceed 1.4 mg/kg/day or a total of 100 mg/day, whichever is less.
Adults & Patients (> 70 kg)
Dosing is not weight-based for patients over 70 kg.
- Initiation: Start at a total daily dose of 40 mg.
- Titration: Maintain the initial dose for at least 3 days before increasing.
- Target Dose: The recommended target dose is 80 mg/day.
- Maximum Dose: The dose may be increased to a maximum of 100 mg/day after 2-4 additional weeks if an optimal response has not been achieved.
Special Populations
Dose adjustments are required in certain populations:
- Moderate Hepatic Impairment (Child-Pugh B): Reduce initial, target, and maximum doses by 50%.
- Severe Hepatic Impairment (Child-Pugh C): Reduce initial, target, and maximum doses by 75%.
- CYP2D6 Poor Metabolizers / Co-administration with Strong CYP2D6 Inhibitors: Initiate at standard doses. Only increase to the target dose if symptoms do not improve after 4 weeks and the initial dose is well-tolerated.
Switching Medications
When switching to atomoxetine from another ADHD medication, such as a stimulant, careful planning is required. A cross-taper, where the previous medication is gradually decreased while atomoxetine is initiated and titrated up, is often recommended. This approach can help manage potential rebound symptoms from stimulant withdrawal and side effects from atomoxetine initiation. Always consult the full prescribing information for both medications before making a switch.
Missed Dose Protocol
If a dose of atomoxetine is missed, the patient should take it as soon as they remember. However, they should not take more than their prescribed total daily dose within a single 24-hour period. If it is nearly time for the next scheduled dose, the patient should skip the missed dose and resume their regular dosing schedule. Double dosing is not recommended.
Safety Alerts
Atomoxetine increased the risk of suicidal ideation in short-term studies in children and adolescents with ADHD. Monitor all patients for clinical worsening, suicidality, or unusual changes in behavior, especially during the initial months of therapy or at times of dose changes.
Other significant warnings include the potential for severe liver injury, serious cardiovascular events (including sudden death in patients with structural cardiac abnormalities), and the emergence of new psychotic or manic symptoms. A thorough cardiovascular and psychiatric history should be obtained before initiating treatment.
Frequently Asked Questions (FAQ)
Why does the dosing strategy change for patients over 70 kg?
For patients weighing 70 kg or less, atomoxetine exposure is proportional to weight, so a mg/kg dosing is most accurate. Above 70 kg, the increase in drug exposure plateaus, so a fixed-dose strategy (starting at 40 mg, targeting 80 mg) is used to prevent over-dosing and is sufficient for therapeutic effect.
What does the “Strong CYP2D6 Inhibitor” setting do?
Checking this box does not change the initial calculated dose but adds a critical warning. Co-administration of atomoxetine with potent CYP2D6 inhibitors (or in patients who are known poor metabolizers) can increase atomoxetine blood levels by 5-fold. The calculator advises caution and slower titration to the target dose only if clinically necessary.
Can Strattera capsules be opened or split?
No. Strattera capsules should not be opened, as atomoxetine is an ocular irritant. If the contents come into contact with the eyes, they should be flushed immediately with water. The powder can also cause skin irritation.
How long does it take for Strattera to become effective?
Unlike stimulants, atomoxetine is not immediate-acting. Some improvement may be seen in the first 1-2 weeks, but it can take 4 to 8 weeks at a therapeutic dose to see the full clinical effect.
Why is the minimum age for this calculator 6 years old?
The safety and efficacy of atomoxetine have not been established in patients under 6 years of age, which aligns with the FDA-approved prescribing information.
What is “Child-Pugh Class B” hepatic impairment?
The Child-Pugh score is a system used to assess the prognosis of chronic liver disease. Class B represents moderate hepatic impairment, which significantly impacts the liver’s ability to metabolize drugs like atomoxetine, necessitating a 50% dose reduction.
Is Strattera (atomoxetine) a controlled substance?
No. Atomoxetine is a selective norepinephrine reuptake inhibitor (SNRI) and is not classified as a controlled substance by the DEA, as studies have shown it to have a low potential for abuse.
What should I do if the calculated dose seems incorrect or too high?
This calculator is an educational tool and not a substitute for clinical judgment. Always double-check calculations and verify inputs. If a calculated dose seems inappropriate, consult the official prescribing information, a clinical pharmacist, or a specialist before prescribing.
References
- U.S. Food and Drug Administration. (2023). STRATTERA® (atomoxetine) capsules prescribing information. Lilly USA, LLC.
- European Medicines Agency. (2022). Strattera (atomoxetine) Summary of Product Characteristics (SmPC).
- Taylor & Francis Online. (2018). Atomoxetine for the treatment of attention-deficit/hyperactivity disorder. Expert Opinion on Pharmacotherapy, 19(11), 1295-1304.
- National Institute for Health and Care Excellence (NICE). (2018). Attention deficit hyperactivity disorder: diagnosis and management (NG87).
