Prozac Weekly (fluoxetine hydrochloride) has been approved by the FDA for the continuation treatment phase of major depressive disorder. The drug is administered on a weekly basis, and it is indicated for patients whose depressive symptoms have stabilized and who require continuing treatment to prevent a relapse, or return of symptoms.
Prozac Weekly contains 90 mg of fluoxetine with an enteric coating that delays release into the bloodstream. Fluoxetine is known as a selective serotonin reuptake inhibitor - it is believed to provide a therapeutic effect by blocking neuronal (nerve cell) uptake of serotonin, resulting in increased levels of the hormone.
Major depressive disorders, which include depression, affect an estimated 340 million people worldwide. If left untreated, the effects of depression can be devastating, robbing people of the energy or motivation to perform everyday activities and, in some cases, leading to suicide. Symptoms of the disorder include feelings of sadness or emptiness, lack of interest or pleasure in nearly all activities, and feelings of worthlessness or inappropriate guilt.
In clinical trials, researchers examined 501 depressed subjects who responded well to 13 weeks of therapy with fluoxetine 20 mg. These subjects were then randomly assigned to treatment with a 90 mg enteric-coated formulation of fluoxetine taken once weekly, fluoxetine at 20 mg daily or a placebo for a 25-week, double-blind period.
Rates of relapse for subjects treated either with the enteric coated or 20 mg formulation of fluoxetine were significantly lower than for those treated with placebo. Additionally, subjects treated with either 90 mg or 20 mg fluoxetine rated significantly better on depression rating scales when compared with subjects assigned to placebo.
The most commonly observed adverse events associated with the use of fluoxetine in Untied States controlled trials for depression, obsessive-compulsive disorder and bulimia combined were the following:
The antidepressant, antiobsessive-compulsive, and antibulemic actions of fluoxetine are presumed to be linked to its inhibition of CNS neuronal uptake of serotonin. Studies at clinically relevant doses in man have demonstrated that fluoxetine blocks the uptake of serotonin into human platelets. Studies in animals suggest that fluoxetine is a much more potent uptake inhibitor of serotonin than of norepinephrine.
Antagonism of muscarinic, histaminergic, and a1-adrenergic receptors has been hypothesized to be associated with various anticholinergic, sedative, and cardiovascular effects of classic tricyclic antidepressant (TCA) drugs. Fluoxetine binds to these and other membrane receptors from brain tissue much less potently in vitro than do the tricyclic drugs. (from Prozac Prescribing Information).
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