1. Clinical Overview
Atomoxetine is a selective norepinephrine reuptake inhibitor (SNRI) specifically approved for the treatment of Attention-Deficit/Hyperactivity Disorder (ADHD). It is a non-stimulant medication, making it a Schedule H drug in India, not under the Narcotic Drugs and Psychotropic Substances (NDPS) Act. Its mechanism is distinct from stimulants like methylphenidate, as it does not act directly on the dopamine system in the reward pathway, resulting in a lower potential for abuse.
| Onset | Duration | Bioavailability |
|---|---|---|
| Therapeutic effects on core ADHD symptoms may take 1 to 4 weeks to become fully apparent, though some effects may be noticed within the first week. | Clinical effect is sustained over 24 hours with once-daily dosing due to its pharmacokinetic profile. | Approximately 63% in extensive metabolizers (most of the population) and 94% in poor metabolizers of CYP2D6. |
2. Mechanism of Action
Atomoxetine is a potent and selective inhibitor of the presynaptic norepinephrine transporter (NET) in the prefrontal cortex. By blocking NET, it increases the synaptic concentration of norepinephrine. This enhanced noradrenergic transmission in the prefrontal cortex is believed to improve attention, focus, and executive function, which are core deficits in ADHD. It has negligible affinity for other neurotransmitter receptors.
3. Indications & Uses
- Attention-Deficit/Hyperactivity Disorder (ADHD) in children (aged 6 years and above)
- Attention-Deficit/Hyperactivity Disorder (ADHD) in adolescents
- Attention-Deficit/Hyperactivity Disorder (ADHD) in adults
4. Dosage & Administration
Adult Dosage: Initial: 40 mg daily. Increase after minimum of 3 days to target dose of 80 mg daily, as a single dose in morning or divided (morning & late afternoon/early evening). Max: 100 mg/day.
Administration: Can be taken with or without food. Swallow capsule whole; do not open, chew, or crush. For patients unable to swallow capsules, the contents may be sprinkled on a small amount of soft food (e.g., applesauce, yogurt) and consumed immediately without chewing. Once-daily dosing is recommended; if experiencing side effects like somnolence, the dose can be divided.
5. Side Effects
Common side effects may include:
- Decreased appetite
- Nausea
- Vomiting
- Dry mouth
- Headache
- Dizziness
- Fatigue
- Somnolence
- Abdominal pain
- Constipation
- Insomnia
- Increased heart rate
- Increased blood pressure
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Monoamine Oxidase Inhibitors (MAOIs) e.g., Phenelzine, Selegiline | Risk of hypertensive crisis, hyperthermia, serotonin syndrome | Contraindicated |
| Strong CYP2D6 Inhibitors (e.g., Paroxetine, Fluoxetine, Quinidine) | Markedly increases atomoxetine plasma levels (similar to a poor metabolizer). Dose adjustment required. | Major |
| Albuterol (Salbutamol) or other Beta-2 Agonists | Potentiates cardiovascular effects (increased heart rate, BP). | Moderate |
| Pressor Agents (e.g., Dopamine, Dobutamine) | Potential for increased hypertensive effect. | Moderate |
| Antihypertensives | May attenuate the effect of antihypertensives. | Moderate |
7. Patient Counselling
- Do take the medication exactly as prescribed by your doctor.
- Do not stop taking the medicine abruptly without consulting your doctor.
- Do inform all your doctors and dentists that you are taking atomoxetine.
- Do not open, chew, or crush the capsule; swallow it whole.
- Do not take with MAO inhibitors or within 2 weeks of stopping them.
8. Toxicology & Storage
Overdose: Symptoms may include somnolence, agitation, hyperactivity, abnormal behavior, gastrointestinal symptoms (nausea, vomiting), tachycardia, hypertension, mydriasis (dilated pupils), and dry mouth. Severe overdose may lead to seizures, QT prolongation, and serotonin syndrome features.
Storage: Store at room temperature (15°C to 30°C). Protect from moisture. Keep in the original container, tightly closed, and out of reach of children.