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Prozac (Generic Fluoxetine)

Dosage

Introduction

Fluoxetine (brand name Prozac) is an antidepressant drug discovered by Eli Lilly and company in 1972. Physicians started using it legally to treat depressed patients in 1986 and has been included by the World-Health Organization (WHO) in its List of Essential-Medicine. It is also marketed for the treatment of premenstrual dysphoric disorder as Sarafem®, fluoxetine hydrochloride.

The drug is used to treat special eating disorder (also known as bulimia nervosa), depressive disorders, panic disorder, obsessive-compulsive disorder, and premenstrual dysphoric disorder (PMDD). Fluoxetine stimulates serotonin production, therefore classified as a selective serotonin-reuptake inhibitors (SSRIs). Using the drug may ameliorate depressed patients’ mood as well as improve sleep and appetite, and also make them more agile finding life interesting again.

Mechanism of action

After the approval of fluoxetine in 1987, its use gained a widespread recognition and became the most prescribed psychotropic drug worldwide. It was initially believed that the drug mechanism of action is solely through the inhibition of serotonergic reuptake until later this was discovered has little facts to back it up.

Fluoxetine has been discovered to inhibit the serotonin transporter protein and also described as a weak norepinephrine reuptake inhibitor. However, the clinical relevance of this norepinephrine inhibition is still obscure. Its antagonistic effect on the 5HT2C receptors has been described as its major activating properties mechanism.

Dosage and formulation

The prescribed dose of fluoxetine is determined by the disorder to be treated. That is why it advisable not to buy fluoxetine without prescription.

Generally, doses between 10 and 60mg/day are used for treating depression and anxiety disorders. For depressive patients, fluoxetine dose is generally between 20 and 60 mg/day. The recommended starting dose for depression is 20 mg/day. It can be titrated to 60 mg/day. For anxiety disorder, 10 mg/day is recommended because of fluoxetine activating properties. 60mg once a day is recommended for bulimia; a higher dose has not been proven to be effective.

Formulation

Capsule: 10mg, 20mg, 40mg

Capsule, delayed-release: 90mg

Tablet:10mg,20mg,60mg

Liquid: 20mg/5mL

Pharmacokinetics

Fluoxetine has an online pharmacokinetic profile. It is well-absorbed after being administered. Following a single oral dose of 40mg, peak plasma concentrations of fluoxetine 15 to 55ng/mL is noticed after 6 to 8 hours. Systemic bioavailability of fluoxetine is not affected by food even though it may delay absorption by 1 to 2 hours and this is not bothering, clinically. Prozac can be ingested with or without food.

Prozac Weekly capsule, a delayed-release formulation, about 90mg, contains enteric-coated pellets that resists dissolution until reaching a segment of the gastrointestinal tract where the pH is above 5.5. The enteric coating delays the effective absorption of fluoxetine 1 to 2 hours relative to the immediate-release formulations.

The interaction between fluoxetine and other highly protein-bound drugs has not fully been evaluated as at the time of writing. The detailed assessment is however important.

Fluoxetine is an equal racemic mixture of R-fluoxetine and S-fluoxetine enantiomers.

The S-fluoxetine enantiomer is excreted more slowly and is the most abundant enantiomer in the plasma at steady state.

Fluoxetine is metabolized in the liver by isoenzymes of the cytochrome-P450-system, including CYP2D6.

Fluoxetine is extensively metabolized in the liver to an identified norfluoxetine, metabolite, and a number of unidentified metabolite. Norfluoxetine, is formed by demethylation of fluoxetine.

The major route of elimination is believed to be hepatic-metabolism to inactive-metabolites that are excreted by our kidneys.

Oral administration of the drug is highly protein-bound, with a wide distribution in the body. It takes an average of 1 to 4 days for fluoxetine to get cleared from the body. But norfluoxetine takes longer, about 7 to 15 days. A strict regulation of dose is advised for patients with hepatic dysfunction.

However, age does not affect fluoxetine pharmacokinetics, making it suitable for use in elderly patients with atypical psychological disorder. Also, its pharmacokinetics is not affected by other clinical conditions like obesity. Fluoxetine and norfluoxetine above 500mg/L concentration are reportedly linked with poorer clinical response compared to lower concentration.

Drug interactions

Just like any other drug, fluoxetine has some drug interactions too.

Patients on routine doses of phenytoin as well as carbamazepine have been discovered to develop clinical anticonvulsant-toxicity and elevated-plasma anticonvulsant-concentrations following the initiation of concomitant–fluoxetine treatment.

The combined use of fluoxetine as well as other CNS–active drugs is yet to be clinically assessed. It is recommended to commence dose from lower concentration and increased progressively until the required dose is reached while the patient's health status is assessed as treatment progresses.

Lithium poisoning and serotonergic effects are possible if lithium is used along with fluoxetine. It is important to check lithium level before commencing treatment.

The use of tryptophan concomitantly with fluoxetine has been reported to cause adverse reactions such as restlessness as well as agitation, and gastrointestinal distress.

Precaution

Prozac should not be used with monoamine oxidase (MAO) inhibitor, methylene blue-injection, tranylcypromine, linezolid and selegiline.

Fluoxetine treatment should not be commenced two weeks after finishing an MAO inhibitor; also MAO treatment should be started 5 weeks after fluoxetine treatment is completed. If this patient is not exerted, patients may experience severe convulsion as well as high blood pressure, agitation or gastrointestinal disorder.

Avoid thioridazine when on fluoxetine treatment and ensure 5 weeks have elapsed after fluoxetine treatment before starting thioridazine. Also, do not use pimozide with fluoxetine. Such a combination may result in complicated heart issues.

Serotonin syndrome may be caused if fluoxetine is ingested along with buspirone, Duragesic, fentanyl, amphetamines or even pain relief drugs like tramadol. Consult with your doctor before you commence treatment, especially if you will buy fluoxetine online.

Teenagers and young adults may get agitated or become irritable due to fluoxetine treatment. In fact, some patients may develop suicidal thoughts and even become depressed. When any of this is observed, contact your specialist for timely intervention.

The use of alcohol is strongly discouraged during fluoxetine treatment.

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