Why Is Prozac Still Prescribed When There Are Newer Antidepressants?

I was on Paxil a few years ago, and it worked great. I was told that Paxil was a “second-generation” Prozac and had fewer side effects. If there are newer and improved antidepressants available in the same class, why is Prozac still prescribed?

Prozac (fluoxetine) was the first drug to be developed in a class of antidepressants called selective serotonin reuptake inhibitors or SSRIs. Other SSRIs include Zoloft (sertraline), Paxil (paroxetine), Luvox (fluvoxamine), and the latest, Celexa (citalopram). These drugs, which share a common effect on neurotransmitters in the central nervous system, represent a major advance in the development of effective antidepressants that have tolerable side effects. (It should be noted that early enthusiasm has been tempered by the realization that sexual side effects and weight gain are turning out to be bigger problems for some patients than anticipated.)

Though they belong to the same class of drugs, there are differences among SSRIs that can have clinical significance — for an individual patient, one drug may have a certain advantage over the others. For example, Paxil is a short-acting drug, persisting in the body for only a few days after discontinuation. Prozac, on the other hand, persists for several weeks. Therefore, Paxil might be a poor choice for someone who tends to skip or forget individual doses because the blood levels drop too much between doses. Someone taking the anticoagulant Coumadin might want to avoid taking Zoloft because of drug interactions that tend to increase the level of Coumadin.

In general, however, the SSRIs can pretty much be considered as equivalent to each other. None can be considered “second-” or “third-generation.” Rather, they are variations on a theme. None has surpassed the others. When Paxil was marketed, the manufacturer stressed in its advertising that the drug was the most potent SSRI (that is, in laboratory experiments a given amount of Paxil more completely inhibited the reuptake of serotonin in brain samples.) This claim, however, had no known clinical significance; it did not mean that Paxil worked any better, faster, or more completely than other SSRIs.

It’s a good thing to have several SSRIs available. Differences in the drugs make one or the other preferable for certain patients. In addition, sometimes one drug is not effective or well tolerated, while another works fine. This can’t be predicted beforehand but must be determined by trial and error.

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