Fluoxetine

Uses

Fluoxetine is used for-

• Depressive illness
• Bulimia nervosa and anorexia nervosa
• Obsessive compulsive disorders
• Pre-menstrual syndrome

Fluoxetine is also used to associated treatment for these conditions: Alcohol Dependency, Anorexia Nervosa (AN), BMI >30 kg/m2, Bulimia Nervosa, Cataplexy, Depression, Bipolar, Major Depressive Disorder (MDD), Myoclonus, Obsessive Compulsive Disorder (OCD), Panic Disorder (With or Without Agoraphobia), Premature Ejaculation, Premenstrual Dysphoric Disorder, Treatment Resistant Depression (TRD)

How Fluoxetine works

The monoaminergic hypothesis of depression emerged in 1965 and linked depression with dysfunction of neurotransmitters such as noradrenaline and serotonin. Indeed, low levels of serotonin have been observed in the cerebrospinal fluid of patients diagnosed with depression. As a result of this hypothesis, drugs that modulate levels of serotonin such as fluoxetine were developed.

Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) and as the name suggests, it exerts it's therapeutic effect by inhibiting the presynaptic reuptake of the neurotransmitter serotonin. As a result, levels of 5-hydroxytryptamine (5-HT) are increased in various parts of the brain. Further, fluoxetine has high affinity for 5-HT transporters, weak affinity for noradrenaline transporters and no affinity for dopamine transporters indicating that it is 5-HT selective.

Fluoxetine interacts to a degree with the 5-HT_2C receptor and it has been suggested that through this mechanism, it is able to increase noradrenaline and dopamine levels in the prefrontal cortex.

Dosage

Fluoxetine dosage

Initial treatment: Recent studies suggest that 20 mg/day of Fluoxetine may be sufficient to obtain satisfactory antidepressant response. Consequently, a dose of 20 mg/day administered in the morning is recommended as the initial dose.

A dose increase may be considered after several weeks if no clinical improvement is observed. Dosage above 20 mg/day, should be administered on a bid schedule (i.e. morning and noon) and should not exceed a maximum dose of 80 mg/day. As with other antidepressants, the full antidepressant effect may be delayed until 4 weeks of treatment or longer. As with many other medications, a lower or less frequent dosage should be used in patients with renal and/or hepatic impairment.

A lower or less frequent dosage should also be considered for patients, such as elderly, with concurrent disease or on multiple medication. A recommended maximum dose for elderly patients is 60 mg per day.

Maintenance treatment: It is generally agreed among expert psychopharmacologists that acute episode of depression requires several months or longer sustained pharmacologic therapy. Fluoxetine is also used in dosage of 60 mg daily for the management of bulimia nervosa.

Side Effects

Gastrointestinal: Nausea, vomiting, dyspepsia, dry mouth, and diarrhoea.

Neurological: Anxiety, nervousness, insomnia/ drowsiness and fatigue.

Others: Excessive sweating, pruritus, skin rashes associated with liver, kidney and lung involvement. It has therefore been advised that Fluoxetine therapy should be discontinued in any patient who develops a skin rash.

Toxicity

In a report that included 234 fluoxetine overdose cases, it was concluded that symptoms resulting from fluoxetine overdose were generally minor and short in duration. The most common overdose adverse effects included drowsiness, tremor, tachycardia, nausea and vomiting, and providing the patient with aggressive supportive care was the recommended intervention.

Despite this evidence, more severe adverse effects have been linked to fluoxetine ingestion although most of these reports involved co-ingestion with other substances or drugs as well as other factors. For example, there is a case report that details a patient who ingested 1400 mg of fluoxetine in a suicide attempt and as a result, experienced a generalized seizure three hours later. In a separate case, a 14 year old patient ingested 1.2 g of fluoxetine and subsequently experienced tonic/clonic seizures, symptoms consistent with serotonin syndrome, and rhabdomyolysis, although the patient did not experience sustained renal injury.

Precaution

As Fluoxetine undergoes hepatic metabolism and renal excretion, it should be used with caution and in reduced doses in patients with impaired hepatic or renal function. Because of its epileptogenic effect, it should be used with caution in patients with epilepsy or a history of such disorders. Fluoxetine may alter glycaemic control and therefore caution is also warranted in diabetic subjects. Depressed patients with suicidal tendencies should be carefully supervised during treatment. Fluoxetine is not usually considered a suitable form of therapy for the depressive component of bipolar (manic depressive) illness as mania may be precipitated.

Interaction

May lead to serotonin syndrome with serotonergic drugs (e.g. triptans, TCAs, fentanyl, tramadol, lithium, buspirone, tryptophan). May increase risk of bleeding with aspirin, NSAIDs, warfarin and other anticoagulants. May increase plasma levels of phenytoin.

Potentially Fatal: May increase risk of serotonin syndrome with concomitant admin or within 14 days of MAOIs withdrawal. May increase the QTc prolonging effect of pimozide and thioridazine.

Food Interaction

• Avoid alcohol.
• Take with or without food.

[Moderate] GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of CNS-active agents.

Use in combination may result in additive central nervous system depression and
MANAGEMENT: Patients receiving CNS-active agents should be warned of this interaction and advised to avoid or limit consumption of alcohol.

Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

Fluoxetine Drug Interaction

Major: amphetamine / dextroamphetamine, amphetamine / dextroamphetamine, lisdexamfetamine, lisdexamfetamineModerate: aspirin, aspirin, pregabalin, pregabalin, metoprolol, metoprolol, cetirizine, cetirizineUnknown: omega-3 polyunsaturated fatty acids, omega-3 polyunsaturated fatty acids, cyanocobalamin, cyanocobalamin, ascorbic acid, ascorbic acid, cholecalciferol, cholecalciferol

Fluoxetine Disease Interaction

Major: depressionModerate: diabetes, hyponatremia, glaucoma, liver disease, mania, platelet function, QT prolongation, seizure disorders, SIADHMinor: renal dysfunction, weight loss

Volume of Distribution

The volume of distribution of fluoxetine and it's metabolite varies between 20 to 42 L/kg.

Elimination Route

The oral bioavailability of fluoxetine is 13

In a bioequivalence study, the Cmax of fluoxetine 20 mg for the established reference formulation was 11.754 ng/mL while the Cmax for the proposed generic formulation was 11.786 ng/ml.

Fluoxetine is very lipophilic and highly plasma protein bound, allowing the drug and it's active metabolite, norfluoxetine, to be distributed to the brain.

Half Life

The half life of fluoxetine is significant with the elimination half-life of the parent drug averaging 1-3 days after acute administration, and 4-6 days after chronic administration. Further, the elimination half life of it's active metabolite, norfluoxetine, ranges from 4-16 days after both acute and chronic administration. The half-life of fluoxetine should be considered when switching patients from fluoxetine to another antidepressant since marked accumulation occurs after chronic use. Fluoxetine's long half-life may even be beneficial when discontinuing the drug since the risk of withdrawal is minimized.

Clearance

The clearance value of fluoxetine in healthy patients is reported to be 9.6 ml/min/kg.

Elimination Route

Fluoxetine is primarily eliminated in the urine.

Pregnancy & Breastfeeding use

Pregnancy: In animal studies, no teratogenicity or harmful effect was found. Because animal reproductive studies are not always predictive of human responses, Fluoxetine should be used in pregnancy only if clearly needed.

Lactation: As Fluoxetine is excreted in human milk, caution should be exercised when Fluoxetine is administered to nursing women.

Contraindication

Fluoxetine Hydrochloride is contraindicated in patients known to be hypersensitive to it.

Monoamine oxidase inhibitors: There have been reports of serious, sometimes fatal reactions (including hyperthermia, rigidity, myoclonus, autonomic instability with possible rapid fluctuations of vital signs and changes of mental status that include extreme agitation progressing to delirium and coma) in patients receiving Fluoxetine in combination with monoamine oxidase inhibitors (MAOIs), and in patients who have recently discontinued Fluoxetine and are then started on MAOIs. Some cases presented with features resembling neuroleptic malignant syndrome. Therefore, Fluoxetine should not be used in combination with MAOI, or within 14 days of discontinuing therapy with MAOI. Since Fluoxetine and its major metabolites have very long elimination half-lives, at least 5 weeks should be allowed after stopping Fluoxetine and before starting MAOI.

Special Warning

Use in children: The use of Fluoxetine in children is not recommended as safety and efficacy have not been established.

Acute Overdose

Symptoms: Nausea, vomiting, seizure, CV dysfunction ranging from asymptomatic arrhythmias to cardiac arrest (including ventricular arrhythmias and nodal rhythm) or ECG changes indicative of QTc prolongation to cardiac arrest, pulmonary dysfunction, signs of altered CNS status ranging from excitation to coma.

Management: Symptomatic and supportive treatment. May admin activated charcoal w/ sorbitol.

Storage Condition

Store between 20-25° C. Protect from light.

Innovators Monograph

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