Fluoxetine (also known by the tradenames Prozac , Sarafem ) is an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class. It is manufactured and marketed by Eli Lilly and Company. In combination with olanzapine it is known as symbyax.

Fluoxetine is approved for the treatment of major depression (including pediatric depression), obsessive-compulsive disorder (in both adult and pediatric populations), bulimia nervosa, panic disorder and premenstrual dysphoric disorder.

Despite the availability of newer agents, fluoxetine remains extremely popular. Over 22.2 million prescriptions for generic formulations of fluoxetine were filled in the United States in 2007,.

The work which eventually led to the discovery of fluoxetine began at Eli Lilly and Company in 1970 as a collaboration between Bryan Molloy and Robert Rathbun. It was known at that time that the antihistamine diphenhydramine shows some antidepressant-like properties. 3-Phenoxy-3-phenylpropylamine, a compound structurally similar to diphenhydramine, was taken as a starting point, and Molloy synthesized dozens of its derivatives. Testing the physiological effects of these compounds in mice resulted in nisoxetine, a selective norepinephrine reuptake inhibitor currently widely used in biochemical experiments.

Later, hoping to find a derivative inhibiting only serotonin reuptake, another Eli Lilly scientist, David Wong, proposed to retest the series for the in vitro reuptake of serotonin, norepinephrine and dopamine. This test, carried out by Jong-Sir Horng in May 1972, showed the compound later named fluoxetine to be the most potent and selective inhibitor of serotonin reuptake of the series. Wong would publish the first article about fluoxetine in 1974. A year later, it was given the official chemical name fluoxetine and the Eli Lilly and Company gave it the trade name Prozac. In February 1977, Dista Products Company, a division of Eli Lilly & Company, presented a new drug request to the U.S. Food and Drug Administration (FDA) for fluoxetine.

A controversy ensued after Lilly researchers published a paper titled "Prozac (fluoxetine, Lilly 110140), the first selective serotonin uptake inhibitor and an antidepressant drug" claiming fluoxetine to be the first selective serotonin reuptake inhibitor (SSRI). Two years later they had to issue a correction, admitting that the first SSRI was zimelidine developed by Arvid Carlsson and colleagues. Fluoxetine made its appearance on the Belgian market in 1986 and was approved for use by the FDA in December 1987. Fluoxetine was the fourth SSRI to make it to market, after zimelidine, indalpine and fluvoxamine. However, the first two were withdrawn due to the side effects, and a vigorous marketing campaign by Eli Lilly made sure that in the popular culture fluoxetine has been perceived as a scientific breakthrough and associated with the title of the first SSRI.

Eli Lilly 's patent on Prozac (fluoxetine) expired in the United States in August 2001, prompting an influx of generic drugs onto the market. Prozac was rebranded "Sarafem" for the treatment of PMDD in an attempt to stem the post-patent decrease in Eli Lilly's sales of fluoxetine.

Fluoxetine has been approved by the FDA for the treatment of major depression , obsessive compulsive disorder, bulimia nervosa and panic disorder. Fluoxetine was shown to be effective for depression in 6-week long double-blind controlled trials, where it also alleviated anxiety and improved sleep. Fluoxetine was better than placebo for the prevention of depression recurrence when the patients, who originally responded to fluoxetine, were treated for a further 38 weeks. Efficacy of fluoxetine for geriatric, as well as pediatric, depression was also demonstrated in placebo-controlled trials.

The peculiar pharmacokinetics of fluoxetine, with its brain levels rising extremely slowly over at least first 5 weeks of treatment (see Pharmacokinetics ), makes it unclear whether the 20-mg/day optimal dose established in the short term (6???8 weeks) trials is applicable for the longer term supportive treatment. One 60-mg dose of fluoxetine per week was found to be equivalent to 20 mg/day for the continuation treatment of responders to 20 mg/day of fluoxetine. and one weekly dose of 80 mg fluoxetine was equivalent to 60 mg/day fluoxetine or 150 mg/day amitriptyline. Furthermore, increase of the dose to 60 mg/day in nonresponders from 20 mg/day brought no additional benefits as compared to continuing the 20 mg/day treatment.

The recent research suggests that a significant part of the resistance to the SSRIs paroxetine (Paxil) and citalopram (Celexa) can be explained by the genetic variation of Pgp transporter. Paroxetine and citalopram, which are Pgp substrates, are actively transported from the brain by this protein. Fluoxetine is not a substrate of Pgp, and thus a switch from paroxetine or citalopram to fluoxetine may be beneficial to the nonresponders.

OCD was successfully treated by fluoxetine in two adult and one pediatric placebo-controlled 13-week trials. The higher doses of fluoxetine appeared to result in better response, while the reverse relationship was observed in the treatment of depression.

According to the manufacturer of Prozac brand of fluoxetine, Eli Lilly , fluoxetine is contraindicated in individuals taking monoamine oxidase inhibitors, pimozide (Orap) or thioridazine (Mellaril). Ibuprofen used in combination with fluoxetine can cause significant intestinal bleeding after a period of use.

Among the common adverse effects associated with fluoxetine and listed in the prescribing information, the effects with the greatest difference from placebo are nausea (22% vs 9% for placebo), insomnia (19% vs 10% for placebo), somnolence (12% vs 5% for placebo), anorexia (10% vs 3% for placebo), anxiety (12% vs 6% for placebo), nervousness (13% vs 8% for placebo), asthenia (11% vs 6% for placebo) and tremor (9% vs 2% for placebo). Those that most often resulted in interruption of the treatment were anxiety, insomnia, and nervousness (1-2% each), and in pediatric trials???mania (2%).

Similarly to other SSRIs, sexual side effects are common with fluoxetine; they include anorgasmia and reduced libido.

In addition, rash or urticaria, sometimes serious, was observed in 7% patients in clinical trials; one-third of these cases resulted in discontinuation of the treatment. Postmarketing reports note several cases of complications developed in patients with rash. The symptoms included vasculitis and lupus-like syndrome . Death has been reported to occur in association with these systemic events.

Akathisia, that is inner tension, restlessness, and the inability to stay still, often accompanied by "constant pacing, purposeless movements of the feet and legs, and marked anxiety," is a common side effect of fluoxetine. More rarely, fluoxetine has been associated with related movement disorders acute dystonia and tardive dyskinesia.

Fluoxetine taken during pregnancy also increases rate of poor neonatal adaptation. A study of fluoxetine administered to newborn mice found that early postnatal exposure of the drug later caused the adult mice to exhibit depressive and anxious behavior similar to those of induced depression, which could be relieved by fluoxetine. The American Association of Pediatrics classifies fluoxetine as a drug for which the effect on the nursing infant is unknown but may be of concern.

Discontinuation syndrome

Several case reports in the literature describe severe withdrawal or discontinuation symptoms following an abrupt interruption of fluoxetine treatment, popularly referred to as "Prozac Poopout". According to a 2007 summary report of available evidence, fluoxetine has the lowest incidence of discontinuation syndrome among several antidepressants including paroxetine and venlafaxine.

See also 
SSRI discontinuation syndrome.

Suicidality

The suicidality of fluoxetine can be determined on various levels of specificity. It can be determined on the antidepressant level, on the SSRI level, and on the fluoxetine level???fluoxetine is an SSRI antidepressant. The more specific level, the fewer studies can be used in a meta-analysis of clinical trials on that level.

Antidepressant

On the antidepressant level, the FDA requires all antidepressants to carry a black box warning stating that antidepressants may increase the risk of suicide in persons younger than 25. This warning is based on statistical analyses conducted by two independent groups of the FDA experts that found a 2-fold increase of the suicidal ideation and behavior in children and adolescents, and 1.5-fold increase of suicidality in the 18???24 age group. The suicidality was slightly decreased for those older than 24, and statistically significantly lower in the 65 and older group. This analysis was criticized by Donald Klein, who noted that suicidality, that is suicidal ideation and behavior, is not necessarily a good surrogate marker for completed suicide, and it is still possible that antidepressants may prevent actual suicide while increasing suicidality.

SSRI

On the SSRI level, see the article SSRI, section Suicidality .

Fluoxetine

On the fluoxetine level, data is harder to come by than on the antidepressant and SSRI levels, as suicidal ideation and behavior in clinical trials are rare. For the above analysis on the antidepressant level, the FDA had to combine the results of 295 trials of 11 antidepressants for psychiatric indications to obtain statistically significant results. Considered separately, fluoxetine use in children increased the odds of suicidality by 50% (not statistically significant due to the low number of cases), and in adults decreased the odds of suicidality by approximately 30% (statistically significant). Similarly, the analysis conducted by the UK MHRA found a 50% increase of odds of suicide-related events, not reaching statistical significance, in the children and adolescents on fluoxetine as compared to the ones on placebo. According to the MHRA data, for adults fluoxetine did not change the rate of self-harm and statistically significantly decreased suicidal ideation by 50%.

The bioavailability of fluoxetine is relatively high (72%), and peak plasma concentrations are reached in 6 to 8 hours. It is highly bound to plasma proteins, mostly albumin .

Fluoxetine is metabolized in the liver by isoenzymes of the cytochrome P450 system, including CYP2D6. The role of CYP2D6 in the metabolism of fluoxetine may be clinically important, as there is great genetic variability in the function of this enzyme among people. Only one metabolite of fluoxetine, norfluoxetine ( N-demethylated fluoxetine), is biologically active.

The extremely slow elimination of fluoxetine and its active metabolite norfluoxetine from the body distinguishes it from other antidepressants. With time, fluoxetine and norfluoxetine inhibit their own metabolism, so fluoxetine elimination half-life changes from 1 to 3 days, after a single dose, to 4 to 6 days, after long-term use. Similarly, the half-life of norfluoxetine is longer (16 days) after long-term use. That means that the full benefits of the current dose a patient receives are not realized for at least a month since its initiation. For example, in one 6-week study, the median time to achieving consistent response was 29 days. Likewise, complete excretion of the drug may take several weeks. During the first week after the treatment discontinuation, the brain concentration of fluoxetine decreases only by 50%, The blood level of norfluoxetine 4 weeks after the treatment discontinuation is about 80% of the level registered by the end of the first treatment week, and 7 weeks after the discontinuation norfluoxetine is still detectable in the blood.

A PET study compared the action of a single dose of fluoxetine on exclusively heterosexual and exclusively homosexual men who attested that their past and present sexual behavior , desires, and fantasies were directed entirely toward women or men, respectively. The study found that in some areas of the brain the metabolic response in these two groups was different. "Both groups, however, did exhibit similar widespread lateralized metabolic responses to fluoxetine (relative to placebo), with most areas of the brain responding in the same direction." They "did not differ on behavioral measures or blood levels of fluoxetine".

Fluoxetine is a selective serotonin reuptake inhibitor and does not appreciably inhibit norepinephrine and dopamine reuptake. Nevertheless, Eli Lilly researchers found that a single injection of a rat with a large dose of fluoxetine also results in a significant increase of brain concentrations of norepinephrine and dopamine. Among SSRIs, 'fluoxetine is the least "selective" of all the SSRIs, with a 10-fold difference in binding affinity between its first and second neural targets (i.e., the serotonin and norepinephrine uptake pumps, respectively).' Anything greater than a 10-fold difference results in insignificant activation of the secondary neuronal targets.

Besides its well-known effects on serotonin, fluoxetine also increases density of endogenous opioid receptors in the central nervous system, which may account for some of its side effects and/or antidepressant profile.

Measurement in body fluids

Fluoxetine and norfluoxetine may be quantitated in blood, plasma or serum to monitor therapy, confirm a diagnosis of poisoning in hospitalized patients or assist in a medicolegal death investigation. Blood or plasma fluoxetine concentrations are usually in a range of 50-500 ??g/L in persons taking the drug for its antidepressant effects, 900-3000 ??g/L in survivors of acute overdosage and 1000-7000 ??g/L in victims of fatal overdosage. Norfluoxetine concentrations are approximately equal to those of the parent drug during chronic therapy, but may be substantially less following acute overdosage, since it requires at least 1???2 weeks for the metabolite to achieve equilibrium.

Fluoxetine and norfluoxetine inhibit many isozymes of the cytochrome P450 system that make drug metabolism possible. Both are potent inhibitors of CYP2D6 (the main enzyme responsible for their metabolism) and mild to moderate inhibitors of CYP1A2, CYP2B6, CYP2C9/ 2C19 , and CYP3A4; furthermore, they inhibit the activity of P-glycoprotein, a type of membrane transport protein that plays an important role in drug transport and metabolism. This extensive effect on the body's pathways for drug metabolism creates the potential for interactions with many commonly used drugs.

The simultaneous use of fluoxetine with triptans, tramadol or other serotonergic agents can result in a rare, but potentially life-threatening adverse drug reaction called serotonin syndrome.

In 1989, Joseph Wesbecker shot and killed eight people and injured 12 others before killing himself at his place of work in Kentucky. Wesbecker had been taking the selective serotonin reuptake inhibitor (SSRI) antidepressant fluoxetine for four weeks before these homicides, and this led to a legal action against the makers of fluoxetine, Eli Lilly. The case was tried and settled in 1994, and as part of the settlement a number of pharmaceutical company documents about drug-induced activation were released into the public domain. Subsequent legal cases have further raised the possibility of a link between antidepressant use and violence.

The Prozac Survivors Support Group created a report on 288 individuals who had suffered adverse effects from Fluoxetine during 1991 and 1992. It showed that most of the cases led to violence against self or other individuals. There were 164 cases in the suicide and suicide ideation category, including 34 complete suicides. There were also 133 cases of crime and violence, which featured 14 murders, nine attempted murders, 39 violent actions, 54 violent preoccupations and 17 crimes. The report also showed that 13 individuals had become addicted to Fluoxetine and 14 cases of alcoholism forming or worsening.

A meta-analysis published in February 2008 combined 35 clinical trials of four newer antidepressants (fluoxetine, paroxetine (Paxil), nefazodone (Serzone) and venlafaxine (Effexor)). These antidepressants belonging to three different pharmacological groups were considered together, and the authors did not analyze them separately. The authors concluded that "although the difference the placebo and antidepressants easily attained statistical significance", it did not meet the criterion for clinical significance, as used by National Institute for Health and Clinical Excellence (UK), "for any but the most severely depressed patients." Some articles in the press using the titles "The creation of the Prozac myth" and "Prozac does not work in majority of depressed patients" presented these general findings about the relative efficacy of antidepressants and placebo as the findings about ineffectiveness of fluoxetine. In a follow-up article, the authors of the meta-analysis noted that "unfortunately, during its initial coverage, the media often portrayed the results as ???antidepressants do not work???, which misrepresented our more nuanced pattern of findings."

As of April 2, 2010, Fluoxetine (Prozac) is one of four antidepressant drugs that the FAA will allow pilots to take without automatically prohibiting them from piloting an aircraft. The others are Sertraline (Zoloft), Citalopram (Celexa), and Escitalopram (Lexapro).

Because of Prozac's wide appeal as a popular antidepressant, the drug is frequently referred to in popular culture, in such media as books, movies, television and music.

Film

• Prozac Nation is a 2001 independent film starring Christina Ricci. It based on an autobiography of the same name by Elizabeth Wurtzel.

Literature

• Book, Listening to Prozac (1993) by psychiatrist Peter D. Kramer.

• The memoir, Prozac Nation (1994) by Elizabeth Wurtzel, was made into a movie of the same name in 2001.

Television

• In the popular HBO series The Sopranos, Tony Soprano receives Prozac and lithium as medications from his psychiatrist Jennifer Melfi, for anxiety attacks, and she adjusts the doses to counteract adverse side effects. In episode 1x12, Melfi discontinues the lithium after Tony's hallucinations about Isabella , a dental exchange student from Italy who, he fantasizes, temporarily lives next door. Ironically, as in episodes 1x12 " Isabella " and 2x13 " Funhouse ", Tony's sleeping dreams and waking hallucinations ??? while he is medicated or over-medicated ??? make him more aware than he otherwise would have been of unpleasant realities about the people and events surrounding him.

Music

• The song Green and Cream from Arjen Lucassen's Guilt Machine album On This Perfect Day (2009) is dedicated to prozac.

• Psychiatric Drug Facts with Dr. Peter Breggin

• Biography of Dr. David T. Wong, one of the inventors of Prozac

• Biography of Dr. Bryan B. Molloy, one of the inventors of Prozac

• Biography of Dr. Ray Fuller, one of the inventors of Prozac

• Trouble in Prozac ??? Fortune Magazine

• U.S. National Library of Medicine: Drug Information Portal ??? Fluoxetine