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Paroxetine
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Paroxetine (trade names Seroxat, Paxil) is a selective serotonin reuptake inhibitor (SSRI) antidepressant. It was released in 1992 by the pharmaceutical company GlaxoSmithKline. It is used to treat major depression, obsessive-compulsive, panic and social anxiety disorders in adult outpatients. Among generic medications, it was the 36th most prescribed drug in 2007, with over 15 million prescriptions written.
The efficacy of paroxetine for depression is comparable to that of older tricyclic antidepressants with fewer side effects and lower toxicity.
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Paroxetine (trade names Seroxat, Paxil) is a selective serotonin reuptake inhibitor (SSRI) antidepressant. It was released in 1992 by the pharmaceutical company GlaxoSmithKline. It is used to treat major depression, obsessive-compulsive, panic and social anxiety disorders in adult outpatients. Among generic medications, it was the 36th most prescribed drug in 2007, with over 15 million prescriptions written.
The efficacy of paroxetine for depression is comparable to that of older tricyclic antidepressants with fewer side effects and lower toxicity. Differences with newer antidepressants are subtler and mostly confined to side effects. It shares the common side effects and contraindications of other SSRIs, with high rates of nausea, somnolence, and sexual side effects. Unlike two other popular SSRI antidepressants fluoxetine and sertraline, paroxetine is associated with a clinically significant weight gain and statistically significant increase in the risk of suicidality in adults. Pediatric trials of paroxetine for depression did not demonstrate efficacy and showed an increase in the risk of harmful outcomes, including episodes of self-harm and potentially suicidal behavior in the paroxetine group compared to placebo. Stopping paroxetine may result in a discontinuation syndrome.
Indications
Approved
Paroxetine is primarily used to treat the symptoms of major depression, obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), panic disorder, generalized anxiety disorder (GAD), social phobia/social anxiety disorder, and premenstrual dysphoric disorder (PMDD).
It was the first antidepressant formally approved in the United States for the treatment of panic attacks.
According to the prescribing information provided by the manufacturer of Paxil brand of paroxetine GlaxoSmithKline and approved by the FDA, the effectiveness of paroxetine in major depressive disorder has been proven by six placebo-controlled clinical trials. For panic disorder, three 10-12-week studies indicated paroxetine superiority to placebo. Similarly, three 12-week trials for adult outpatients with social anxiety disorder demonstrated better response to paroxetine than to placebo.
Unapproved/off-label/investigational
Moreover, studies have suggested that paroxetine can in fact be used in the treatment of premature ejaculation. In particular, intravaginal ejaculation latency time (IELT) found to increase with a 6-13-fold, which was somewhat longer than those of a predessor.. the delay achieved by the treatment with other SSRIs (fluvoxamine, fluoxetine, sertraline and citalopram). However, paroxetine taken acutely ("on demand") 3–10 hours before coitus resulted only in a "clinically irrelevant and sexually unsatisfactory" 1.5-fold delay of ejaculation and was inferior to clomipramine, which induced a fourfold delay.
There is also evidence that paroxetine may be effective in the treatment of compulsive gambling and hot flashes.
In two double-blind studies of bipolar disorder patients, addition of paroxetine to a mood stabilizer had no advantages over addition of placebo. Benefits of paroxetine prescription for diabetic neuropathy or chronic tension headache. are uncertain.
Pharmacology
Paroxetine is the most potent and one of the most specific selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitors (SSRI). This activity of the drug on brain neurons is thought to be responsible for its antidepressant effects.
Paroxetine is a phenylpiperidine derivative which is chemically unrelated to the tricyclic or tetracyclic antidepressants. In receptor binding studies, paroxetine did not exhibit significant affinity for the adrenergic (a1, a2, ß), dopaminergic, serotonergic (5HT1, 5HT2), or histamine receptors of rat brain membrane. A weak affinity for the muscarinic acetylcholine and noradrenaline receptors was evident. The predominant metabolites of paroxetine are essentially inactive as 5-HT reuptake inhibitors.
Chemistry
Paroxetine hydrochloride is an odorless, off-white powder, having a melting point range of 120° to 138°C and a solubility of 5.4 mg/mL in water.
Formulations
Paroxetine CR (controlled release) was shown to be associated with a lower rate of nausea during the first week of treatment than paroxetine immediate release. However, the rate of treatment discontinuation due to nausea was not significantly different.. Since both Paxil and Paxil CR are generally dosed once daily, the benefit of Paxil CR has been debated, especially given the significant cost difference between (generic) Paxil and (brand-only) Paxil CR.
Side effects
Among the common adverse effects associated with paroxetine treatment of depression and listed in the prescribing information, those with the greatest difference from placebo are nausea (26% on paroxetine vs 9% on placebo), somnolence (23% vs. 9% on placebo), ejaculatory disturbance (13% vs. 0% on placebo), other male genital disorders (10% vs. 0% on placebo), asthenia (15% vs. 6% on placebo), sweating (11% vs. 2% on placebo), dizziness (13% vs. 6% on placebo), insomnia (13% vs. 6% on placebo), dry mouth (18% vs. 12% on placebo), constipation (14% vs. 9% on placebo), and tremor (8% vs. 2% on placebo).
General side effects are mostly present during the first 1–4 weeks while the body acquires a tolerance to the drug, although once this happens, withdrawal can cause a rebound effect with symptoms re-emerging in an exaggerated form for very long periods of time. Almost all SSRIs are known to cause either one or more of these symptoms. A person receiving paroxetine treatment may experience a few, all, or none of the following side-effects, and most side-effects will disappear or lessen with continued treatment, though some may last throughout the duration. Side effects are also often dose-dependent, with fewer and/or less severe symptoms being reported at lower dosages, and/or more severe symptoms being reported at higher dosages. Increases or changes in dosage may also cause symptoms to reappear or worsen.
On 9 December 2004 the European Medicines Agency's (EMEA) Committee for Medicinal Products for Human Use (CHMP) informed patients, prescribers and parents that paroxetine should not be prescribed to children. CHMP gave a warning to prescribers recommending close monitoring of adult patients at high risk of suicidal behaviour and/or suicidal thoughts. In other words, CHMP does not prohibit use of paroxetine with adults but stresses extreme caution in actual usage. Also withdrawal reactions upon stopping treatment is mentioned and therefore it is recommended to gradually reduce the dose over several weeks or months if decision of withdrawal is made.
A statistical analysis of paroxetine clinical trials in children and adolescents was conducted by the FDA in 2004. It indicated a statistically significant 2.7-fold raise in suicide behavior and ideation as compared to placebo. The trend for increased suicidality was observed in both trials for depression and for anxiety disorders.
Cases of akathisia and activation syndrome have been observed during paroxetine treatment.
Rarely serotonin syndrome, a severe adverse effect may occur.
Other
- Teratogenicity: Pregnant women are advised not to take the drug due to possible fetal heart defects.
Paroxetine and other SSRIs have been shown to cause sexual side effects in most patients, both males and females.
Schmitt et al. (2001) suggested that paroxetine negatively affects cognition (i.e., IQ). In their study, healthy participants given paroxetine for 14 days (20mg for days 1–7 and 40mg days 8–14) showed poorer recall of words on day 14 compared to those receiving a placebo. Schmitt and co-workers, however, did not account for significant differences in verbal recall at baseline between those receiving paroxetine and those receiving a placebo, differences which produced the significant finding. Furthermore, participants receiving paroxetine recalled as many words at baseline as they recalled on day 14. Accordingly, the conclusion that paroxetine affects verbal recall was unwarranted.
Discontinuation syndrome
Many psychoactive medications can cause withdrawal symptoms upon discontinuation from administration. Evidence has shown that paroxetine has among the highest incidence rates and severity of SSRI discontinuation syndrome of any medication of its class. Common paroxetine withdrawal symptoms include repeated electrical shock sensations of the brain and body (see "brain zaps"), vertigo, hot flashes and a rebound of panic symptoms worse than before treatment. Suicidal ideation is a frequently reported experience in those withdrawing from SSRIs. For those experiencing extreme and unusual difficulty discontinuing paroxetine, it is recommended that an SSRI with a longer half-life, such as fluoxetine, be administered for approximately two weeks, then discontinued, to lessen symptoms.
For 10 years, GlaxoSmithKline's marketing of the drug stated that it was "not habit forming". In 2002, the U.S. Food and Drug Administration published a new product warning about the drug, and the International Federation of Pharmaceutical Manufacturers Associations (IFPMA) declared GSK guilty of misleading the public about paroxetine on US television. The quoted Charles Medawar, head of : "This drug has been promoted for years as safe and easy to discontinue.... The fact that it can cause intolerable withdrawal symptoms of the kind that could lead to dependence is enormously important to patients, doctors, investors, and the company. GlaxoSmithKline has evaded the issue since it was granted a licence for paroxetine over 10 years ago, and the drug has become a blockbuster for them, generating about a tenth of their entire revenue. The company has been promoting paroxetine directly to consumers as 'non-habit forming' for far too long." In 2006 it was the fifth-most prescribed antidepressant in the United States retail market, with more than 19.7 million prescriptions. Paroxetine prescribing information posted at GlaxoSmithKline now acknowledges the occurrence of a "discontinuation syndrome" including "serious discontinuation symptoms."
Warning for pregnant women
Pregnant women and those who might become pregnant should avoid taking the antidepressant Paxil because of a high risk of birth defects, according to a committee of obstetricians who published their opinion in the December 2006 issue of the journal Obstetrics & Gynecology.
The obstetric practice committee of the American College of Obstetricians and Gynecologists said pregnant women should not take Paxil because two previous studies found that the drug posed up to double the risk of heart defects in fetuses.
Neonatal withdrawal symptoms from Paxil have also been documented from mothers taking Paxil during pregnancy.
Controversy
A British Government parliamentary inquiry into a number of prescription and over the counter drugs noted problems with SSRI antidepressants including withdrawal, suicidal thoughts and other adverse effects. The inquiry found that paroxetine (Paxil, Seroxat) has, more commonly than other SSRI antidepressants, a very devastating impact on some users lives.
Since the FDA approved paroxetine in 1992, approximately 5,000 U.S. citizens have sued GSK. Most of these people feel they were not sufficiently warned in advance of the drug's side effects—particularly the withdrawal syndrome discussed above, after GSK had specifically advertised the drug as non-habit forming
In the UK since 2001 lawsuits have been filed representing people who have been prescribed Seroxat. They allege that the drug has serious side effects, which GlaxoSmithKline downplayed in patient information.
In early 2004, GSK agreed to settle charges of consumer fraud for $2.5 million (a tiny fraction of the over $2.7 billion in yearly Paxil sales at that time). The legal discovery process also uncovered evidence of deliberate, systematic suppression of unfavorable Paxil research results. One of GSK's internal documents had said, "It would be commercially unacceptable to include a statement that efficacy [in children] had not been demonstrated, as this would undermine the profile of paroxetine". In March 2004 the FDA ordered a black box warning placed on SSRI and other antidepressants, warning of the risk for potential suicidal thinking in children and adolescents. ABC News reported that the prescribing of these medications to children subsequently dropped by 20 percent.
According to the Centers for Disease Control and Prevention's Annual Summary of Vital Statistics, the suicide rate rose more than 18 percent in those 1 to 19 years old, from 2.2 per 100,000 in 2003 to 2.6 per 100,000 in 2004. In those 15 to 19 years old, the figures reflected a more than 12 percent rise in suicide, from 7.3 per 100,000 in 2003 to 8.2 per 100,000 in 2004. This led many experts to conclude that the warning, and subsequent reduction in the use of antidepressants, led to an increased suicide rate in this age group. The finding is consistent with an earlier finding, reported to the 2003 FDA Advisory Committee by Dr David Shaffer, that suicide rates in the United States fell during the 1990s, in line with the introduction of SSRIs.
On January 29 2007, the BBC broadcast a fourth documentary in its Panorama series about the drug Seroxat. This programme, entitled Secrets of the Drug Trials, focused on three GSK paediatric clinical trials on depressed children and adolescents. Data from the trials show that Seroxat could not be proven to work for teenagers. Also, one clinical trial indicated that adolescents were six times more likely to become suicidal after taking it.
In May 2007 a US court approved a settlement in a class action lawsuit brought on behalf of everyone in the United States who purchased Paxil or Paxil CR prescribed for a minor. The lawsuit alleged that GlaxoSmithKline promoted Paxil or Paxil CR for prescription to children and adolescents while withholding and concealing material information about the medication's safety and effectiveness for minors. GSK denied all claims. The settlement terms entitled everyone, who previously purchased Paxil or Paxil CR for their child or ward, to recover up to 100% of the documented out-of-pocket expenses or $100, if documentation was not available.
The court documents released as a result of one of the lawsuits in October 2008 indicated that GSK "and/or researchers may have suppressed or obscured suicide risk data during
clinical trials" of paroxetine. One of the investigators, "Charles
Nemeroff, former Chairman of the Department of Psychiatry at Emory University, was the first big
name 'outed' ...In early October, Nemeroff resigned from Emory amid revelations that he had received over $960,000 from GSK in 2006, yet reported less than $35,000 to the school. Subsequent investigations revealed payments totaling more than $2.5 million from drug companies between
2000 and 2006, yet only a fraction was disclosed."
In 2008, it was also suggested that Paroxetine could affect fertility in male patients.
The suppression of unfavorable research findings on Paxil by GSK — and the legal discovery process that uncovered it — is the subject of Alison Bass's 2008 book Side Effects: A Prosecutor, a Whistleblower, and a Bestselling Antidepressant on Trial.
See also
Footnotes
External links
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- from medlibrary.org
- , BBC Panorama investigation
- , Washington Post, April 18, 2004
- , Hartford Advocate, Sept 11, 2008
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