Adverse Drug Reactions and Metabolism

Adverse Drug Reactions and Metabolism

There is an old Chinese proverb that says, “It is easy to get a thousand prescriptions but hard to get one single remedy.” More and more frequently, when we visit a doctor because of an ache or pain, the doctor and patient are less concerned with determining a way to handle the cause of the problem than in finding a way, normally with a prescription drug, to address the symptoms and attempt to give the patient some relief.

All too often, one prescription leads to another prescription meant to handle the side effects created by the first prescription, and so it goes until we are taking six, eight or ten different medications and still have the original problem along with a host of new problems. According to the Agency for Healthcare Research and Quality (“AHRQ”), from 1994 to 2005, the number of prescriptions purchased increased 71% (from 2.1 billion to 3.6 billion), compared to a US population growth of 9%. The average number of retail prescriptions per capita increased from 7.9 in 1994 to 12.3 in 2005. Taking drugs to address side effects from other drugs is not going to help anyone regain health and can actually do the opposite, but this is not the only issue. The number of adverse drug reactions has also escalated.

The AHRQ states that in 2004, adverse drug reactions were noted in 1,211,100 hospital stays. 90% of these were not reactions to drugs that were purchased on the street but were caused by drugs properly prescribed and administered. The reactions ranged from discomfort to death. And this number does not include the estimated millions of others that experience adverse drug reactions but don't end up in the hospital. For years, the perplexing question for doctors was why one person, taking the exact same drugs as another, experiences an adverse drug reaction and the other doesn't?

Genetics scientists believe that the explanation for many of these adverse drug reactions may be the way that drugs are metabolized in each of us. (This is not to say that many unneeded drugs are prescribed that just treat symptoms-not the actual cause.) Simply stated, metabolism is the action of complex proteins called enzymes breaking down medications and drugs and allowing the body to utilize them. When a drug or medication is taken orally, it usually travels from the stomach to the liver, where most drugs are metabolized by enzymes. If properly metabolized, the drug is then able to be used by the body. In that group of enzymes in the liver, an enzyme named CYP3A metabolizes the largest number of drugs, followed closely by the CYP2D6 enzyme, which is responsible for the metabolism of an estimated 25 percent of all prescription drugs including many antidepressant, antipsychotic and opiate drugs.

An example of how this can work is that your doctor prescribes Drug A and Drug B and both are metabolized by the CYP2D6 enzyme. Drug A inhibits the operation of the CYP2D6 enzyme and prevents it from fully metabolizing Drug B. Drug B is not metabolized fully and causes unpleasant side effects or, more seriously, adverse drug reactions. There are also drugs that increase the rate of metabolism of other drugs. For example, if someone is taking a blood thinner drug and is prescribed an antidepressant that causes the rapid metabolism of the blood thinner drug, the result will be that, instead of being released in the body slowly, the blood thinner drug is released quickly and is much less effective for thinning blood.

This can lead to blood clots or strokes. There are also drugs that slow the metabolism of other drugs and this can reduce the perceived effectiveness of the drug or create everything from uncomfortable side effects to adverse drug reactions. Not only drugs but some herbs, vitamins, and foods can also affect enzyme activity. For example, grapefruit juice can act as an inhibitor of CYP3A, the enzyme responsible for the metabolism of the largest number of generic drugs, and St. John’s wort has been found to increase the activity of the CYP3A enzyme.

The result of all these drugs trying to get through the same small pathway is that all too often people experience one or more of the many side effects listed on a drug’s label and, more and more, adverse drug reactions. The next time you go to the doctor and a drug is suggested, ask if this drug is going to handle the cause of the problem you are having, what are the side effects of the drug and if the doctor is comfortable that the drug is not going to create metabolism problems for other drugs, vitamins and/or food that you are ingesting.

If you are not satisfied with the answers from the doctor, then you should consider getting another doctor.

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