Drug interactions start when medicines compete for the same way out of the body, use the same organ (such as the liver) for removal or even have unknown or later discovered ways of working or acting that are different from what they are usually prescribed for. One of the medicines may be blocked from removal and increase in blood level, an unexpected increase in a body chemical may happen or unseen toxicity may result.
This DOES NOT mean that they are bad medicines, it simply means that they don’t get along well and that there are combinations that you and your doctor and pharmacist should be aware of. Sometimes what your doctor and pharmacist call drug-drug interactions can be managed by delaying when you take one medicine and then start another. Sometimes two drugs should not be used together or only used if the benefit outweighs a delayed or a less serious risk.
A good example of this was recently in the news from the FDA. The two medicines which are of concern are Zyvox (linezolid—an antibiotic used in pneumonia, MRSA and VRE infections and various skin infections) and methylene blue (sometimes used in emergency situations in high doses in cyanide poisoning, methemoglobinemia and Ifosfamide nerve toxicity). These two medicines have good and clear used which are FDA approved. The problem is that they both can act to inhibit the enzyme that your body uses to break down serotonin.
Many people know that they are taking an SSRI for depression. What this means is that the medicine selectively inhibits the way that nerves remove serotonin from the place that it works, leading to a higher serotonin level. The benefit of this is that it helps improve thinking and mood in people battling depression. Turns out that many medicines used to help psychiatric troubles can interact. Some important drugs include: Anafranil, Ascendin, Aventyl, Buspar, Celexa, Cymbalta, Effexor, Elavil, Endep, Norpramin, Lexapro, Ludiomil, Luvox, Pamelor, Paxil, Pristiq, Prozac, Sarafem, Serotonergics, Serzone Desyrel, Sinequan, Surmontil, Tofranil, Viibryd and Remeron, Vivactil, Wellbutrin, Zoloft and Zyban.
The problems arise when we have too much serotonin. Excess serotonin has an effect on the nerves. When serotonin levels continue to increase further, you can have a serotonin syndrome which can show up as confusion, memory problems, hyperactivity, twitching muscles, sweating, shaking, diarrhea, fever, incoordination and with extreme levels, even death. Other known medicines that work as monamine oxidase inhibitors (MAOI type drugs) include Emsam, Eldepryl, Marplan, Nardil and Parnate.
The true impact of this interaction will be most probably seen in hospitals since Zyvox in given by vein (intravenously) and methylene blue is given in higher doses in oncology and as an antidote in emergency rooms. In concert with your doctor, this possible interaction can certainly be managed. If you require Zyvox to treat a serious infection, it may mean that in an emergency situation where the benefit (for example treating a life-threatening infection) outweighs the risk of serotonin toxicity, the antidepressant would be stopped immediately and the patient monitored closely for toxicity for two weeks or 24 hours after the last dose of Zyvox. Since Prozac stays in your system longer, you would need to be monitored for possible toxicity for 5 weeks.
If there was a situation where Zyvox was required, but it was not an emergency, the serotonin increasing medicine could be stopped, and another antidepressant (one with no effect on serotonin started if required) roughly two weeks before the Zyvox (5 weeks if you were taking Prozac). Your original antidepressant which worked on serotonin could be restarted 24 hours after the last dose of Zyvox. While this is a little complicated, these steps help make sure there is no withdrawal reaction to stopping the serotonin increasing medicine AND that the medicine is out of your system before Zyvox is used.
Remember that serious reaction to medicines can be reported to the FDA by calling 1-800-332-1088. You can find a full list of possible interacting medicines and other medicines (beside Zyvox and methylene blue) that can act as MAO inhibitors that could lead to too much serotonin at www.fda.gov and search Zyvox interaction. Talk to your doctor BEFORE making any changes to the medicines you take!