1. Clinical Overview
Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) antidepressant. It is a first-line agent for the treatment of major depressive disorder (MDD), obsessive-compulsive disorder (OCD), bulimia nervosa, and panic disorder. It works by increasing the availability of serotonin in the synaptic cleft, thereby improving mood, appetite, energy levels, and restoring interest in daily life. The 10mg strength is often used for initiation, dose titration, maintenance in sensitive patients, and in pediatric populations.
| Onset | Duration | Bioavailability |
|---|---|---|
| Therapeutic antidepressant effects typically begin within 1-4 weeks, though full benefit may take up to 8-12 weeks. Some symptoms like sleep or appetite may improve earlier. | Long-acting due to its active metabolite, norfluoxetine, which has a half-life of 7-15 days. Effects persist well beyond the dosing interval, allowing for once-daily administration. | Approximately 70-80% after oral administration. |
2. Mechanism of Action
Fluoxetine selectively inhibits the presynaptic neuronal reuptake of serotonin (5-hydroxytryptamine, 5-HT) into the presynaptic terminal. This inhibition is potent and specific, with minimal direct effect on the reuptake of norepinephrine or dopamine. The increased synaptic availability of serotonin enhances serotonergic neurotransmission, which is believed to mediate its antidepressant and anti-obsessional effects.
3. Indications & Uses
- Major Depressive Disorder (MDD)
- Obsessive-Compulsive Disorder (OCD)
- Bulimia Nervosa (for reducing binge-eating and purging behaviors)
- Panic Disorder with or without agoraphobia
4. Dosage & Administration
Adult Dosage: MDD/OCD: Initial dose 20mg once daily in the morning, may be increased after several weeks. The 10mg dose is used for initiation in patients prone to side effects (e.g., high anxiety) or for maintenance in some patients. Maximum: 80mg/day (in divided doses for higher doses). Bulimia: 60mg once daily in the morning. Panic Disorder: Start at 10mg/day, may increase to 20mg/day after one week.
Administration: Administer orally, with or without food. Usually taken in the morning to minimize insomnia. If causing drowsiness, can be taken in the evening. The capsule/tablet should be swallowed whole with a glass of water. Do not crush or chew. For the liquid formulation, use the measuring device provided.
5. Side Effects
Common side effects may include:
- Nausea
- Headache
- Insomnia
- Drowsiness/somnolence
- Anxiety/nervousness
- Dry mouth
- Sweating
- Fatigue/asthenia
- Diarrhea or loose stools
- Decreased appetite
- Tremor
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Monoamine Oxidase Inhibitors (MAOIs) - Phenelzine, Tranylcypromine, Moclobemide | Risk of severe, potentially fatal serotonin syndrome (hyperthermia, rigidity, myoclonus, autonomic instability). | Contraindicated |
| Pimozide, Thioridazine | Fluoxetine inhibits CYP2D6, increasing levels of these drugs, leading to serious QT prolongation and ventricular arrhythmias (torsades de pointes). | Contraindicated |
| Other Serotonergic Drugs - Tramadol, Linezolid, Triptans, TCAs, other SSRIs/SNRIs, Fentanyl, Lithium, St. John's Wort | Increased risk of serotonin syndrome. | Major |
| Warfarin and other Anticoagulants | Fluoxetine may displace warfarin from protein binding sites and affect metabolism, increasing INR and risk of bleeding. | Major |
| CYP2D6 Substrates - Codeine, Tamoxifen, Metoprolol, Flecainide, Propafenone, Risperidone | Fluoxetine is a potent CYP2D6 inhibitor, can significantly increase plasma levels of these drugs, leading to toxicity or reduced efficacy (in case of prodrugs like codeine, tamoxifen). | Major |
| Drugs metabolized by CYP3A4 - Carbamazepine, Cyclosporine | Fluoxetine may inhibit their metabolism, increasing levels. | Moderate |
| NSAIDs, Aspirin, Clopidogrel | Increased risk of gastrointestinal bleeding due to synergistic effect on platelet serotonin. | Moderate |
| Antidiabetics (Insulin, Sulfonylureas) | Fluoxetine may alter blood glucose levels; dosage adjustment may be needed. | Moderate |
7. Patient Counselling
- DO take the medication exactly as prescribed, at the same time each day.
- DO NOT stop taking fluoxetine abruptly without consulting your doctor, as this may cause withdrawal-like symptoms (dizziness, nausea, headache, paresthesia, anxiety).
- DO inform all your healthcare providers (doctors, dentists, surgeons) that you are taking fluoxetine.
- DO NOT consume alcohol while on this medication.
- DO use caution when driving or operating machinery until you know how the medicine affects you.
- DO keep all follow-up appointments with your doctor to monitor progress and side effects.
8. Toxicology & Storage
Overdose: Nausea, vomiting, agitation, restlessness, hypomania, seizures, tachycardia, ECG changes (including QT prolongation), drowsiness leading to coma. Serotonin syndrome symptoms may be prominent. Deaths have been reported, usually in combination with other drugs/alcohol.
Storage: Store at room temperature (15°C to 30°C), protected from light and moisture. Keep in the original container, tightly closed. Keep out of reach and sight of children. Do not use after the expiry date printed on the pack. Do not flush medications down the toilet or pour them into a drain unless instructed to do so.