Recently, the d r u g industry, or Big Pharma as it is often called, has come under a lot of critical scrutiny. In books like "The Truth about the Drug Industry" by Marcia Angell (former editor of the New England Journal of Medicine) and "Overdosed America," by John Abramson (a New England family physician), the industry that makes chemical medicines has been placed under a microscope. Quite apart from using patents to jack up prices, or manipulating doctors and the public with false or exaggerated information, Big Pharma has been failing to tell us about some very bad side-effects of its products – like antidepressants of the Prozac family increasing violent and suicidal behaviour, or anti-inflammatory drugs such as Vioxx bringing on heart attacks.

But that's not the end of it. There is a whole new aspect of drug use that's beginning to cause alarm. For years, there has been a growing interest in knowing where medicinal drugs actually go when they leave our bodies, and what they do when they get there.

As I mentioned in my last column, every medicine that we take into our bodies has to leave our bodies eventually. Sewage treatment plants can get rid of bacteria and viruses that cause disease, but they're not designed to handle chemicals like drugs for human or veterinary therapy. Consequently most of these substances get out into the water supply. But what to they do there?

There's an absolutely enormous amount that we don't know. But here's an example of something  we do know. A small group of drugs – each used for a very different medical purpose – has been shown to block the excretion of poisons by certain animals, especially those living in water. Verapamil, a cardiac drug known as a "calcium channel blocker," belongs to this group. Verapamil blocks the ability of animals to use their "multidrug transporters" (MDTs) – chemical pathways that are like bouncers at a night club; they block poisonous chemicals from getting in, or they get rid of them if they break in and start making trouble. If the MDT isn't working properly, a concentration of a poison that would be harmless suddenly becomes life-threatening. One experimenter added tiny amounts of verapamil to river water, followed by a toxin at an extremely low level, that normally would cause no effect; in the presence of verapamil, this trace of toxin caused "dramatic avoidance attempts by the fish, escalating to the point of frantic escape attempts."

Other drugs that block the MDTs of aquatic animals are trifluoroperazine, an antipsychotic drug, quinidine and amiodarone, both used to block irregular heart rhythms, and cyclosporine, used to stop the rejection of transplanted organs. Each drug, while harmless in itself, leads to a sudden increase in the poisonous effect of other chemicals. A very small number of natural substances – e.g. grapefruit juice and the hormone progesterone – can also do this.

The bottom line: everything we do to treat ourselves has some sort of effect on the rest of the living creatures around us. To think otherwise is folly.

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