What is Pristiq (Desvenlafaxine)

Pristiq is the brand name for the molecule “desvenlafaxine,” one of the new generation antidepressants. It was introduced in late 2008 by Wyeth (now part of Pfizer Inc.). Wyeth also developed and marketed Effexor, which is the brand name for the molecule “venlafaxine.” Pristiq and Effexor are closely related molecules affecting brain levels of serotonin and norepinephrine, neurotransmitters believed to be linked to mood. Those neurotransmitters are cyclically released and absorbed between nerve cells in the brain each time a nerve cell conveys a signal. Theoretically, lower neurotransmitter levels between nerve cells leads to lowered mood.

Drugs like Pristiq and Effexor are believed to create the effect of increasing between-cell serotonin and norepinephrine levels by reducing their re-absorption between firings of nerve cells. Pristiq and Effexor operate by blocking proteins that enable nerve cells’ re-absorption of these neurotransmitters, i.e. they block “reuptake” proteins, thereby leaving more active neurotransmitters in the gaps between nerves (synapses). Since the neurotransmitters affected are serotonin and norepinephrine, Pristiq and Effexor are classified as serotonin-norepinephrine reuptake inhibitors (SNRIs).

Pristiq and Effexor operate with essentially the same active ingredient. Shortly after a patient takes venlafaxine (Effexor), it is broken down (“metabolized”) into mostly desvenlafaxine, the molecule sold as Pristiq. Desvenlafaxine is a synthetic form of Effexor’s isolated major active metabolite. When most people with normal metabolisms take venlafaxine (Effexor) – 70% of the benefit comes from its being metabolized into desvenlafaxine (Pristiq), so the effects of both Effexor and Pristiq are very similar. This means that when taking Pristiq, a patient is simply skipping breaking down the combined molecules comprising Effexor and undergoing essentially a treatment of Effexor’s active ingredient.

Effexor, which was introduced in 1993, will be losing its patent in 2013. By introducing Pristiq, Wyeth/Pfizer has been able to, in a way, extend the patent of their blockbuster antidepressant.

Since Effexor and Pristiq rely upon the same active ingredient, with essentially the same effect, they also share similar side effects and risks. One of these shared side effects is the risk of birth defects associated with taking antidepressants in the early stages of pregnancy.

Pristiq, in particular, has been the subject of a few animal studies which found that the medication does have an impact on animal birth defects. The side effects in humans, however, is still relatively unknown. Because of this, the FDA has classified Pristiq as a “Category C” drug, which means that animal reproduction studies have shown an adverse effect on the fetus and there are no adequate well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risk. The Pregnancy Categories measure the teratogenic effects a drug has on a fetus (teratogenic or embryocidal or other). Teratogenic means that a drug or other substance is capable of interfering with the development of a fetus. Embryocidal pertains to the killing of an embryo.

Health providers are still allowed to prescribe Pristiq to pregnant women, only if they believe the benefits of the drug outweigh the risks. With the risks still relatively unknown however, it is difficult to gauge whether any benefit is greater than any potential risk to an unborn child.

On July 19, 2006, the FDA issued a Public Health Advisory for SSRIs, including Celexa (citalopram), Fluvoxamine, Lexapro (escitalopram), Symbyax (olanzapine and fluoxetine) and Zoloft (sertraline) based on a study that suggests there may be additional risks of SSRI medications during pregnancy. In this study, PPHN (Persistent pulmonary hypertension of the newborn) was six times more common in babies whose mothers took an SSRI antidepressant after the 20th week of the pregnancy compared to babies whose mothers did not take an antidepressant.