Each of your medications may be affecting the way others work, leading to harmful side effects and complications.
Are you taking more than one drug? Are you taking some different types of medications? Are you seeing several different doctors? If so, you may have an increased risk of drug interactions, which occur when a drug, supplement, or even a food affects how your body processes a drug. Such interactions can make a drug more potent, so that a standard dose becomes an overdose, or it can make it less potent or totally ineffective.
“It’s critical that people learn about their medications and become aware of their response to them,” says Dr. Shobha Phansalkar, an assistant professor of medicine at Harvard Medical School. His research focuses on exploring ways in which people can better manage their medications to avoid side effects.
How Drug Interactions Occur
The term “drug interactions” is somewhat misleading. Drugs do not combine in the body to produce chemical reactions. Instead, a drug, supplement or food can affect the duration of medication in the body, often stimulating or inhibiting the production of specific enzymes in the liver or intestine. These enzymes are part of the cytochrome p450 system, which plays an important role in the metabolism of many drugs. Drug interactions usually occur in one of the following ways:
Interactions with other drugs. Interactions between two drugs occur when one drug affects the cytochrome enzyme that processes the other. For example, the antibiotic metronidazole (Flagyl) inhibits the enzyme CYP2C, which breaks down warfarin (Coumadin). If both medications are taken together, the anticoagulant canlinger in the body, increasing the risk of severe bleeding. The anti-convulsive drug phenytoin (Dilantin) stimulates over-production of CYP3A4, the enzyme that metabolizes estradiol, a component of low-dose contraceptives. In this case, contraceptives are eliminated more rapidly in women taking phenytoin, reducing their effectiveness and increasing the chances of an unplanned pregnancy.
In other cases, two drugs taken for different purposes can have the same effect, producing something like an overdose. A common example of this is when over-the-counter analgesics-aspirin, ibuprofen (Motrin), naproxen (Aleve) and, to a lesser extent, acetaminophen (Tylenol) are taken with blood thinners such as warfarin and clopidogrel (Plavix). Since analgesics also have anti-coagulation effects, the combination can result in severe bleeding.
Interactions with nutrients. Several foods can also block or stimulate the enzymes that break down drugs. People who wash atorvastatin (Lipitor) or simvastatin (Zocor) with large amounts of grapefruit juice may experience muscle pain and other side effects of the statin “overdose”, because the juice inhibits the enzyme that clears statins. Fish oil supplements may have a similar effect when taken with warfarin, increasing the risk of severe bleeding. Iron supplements may decrease the effects of levoxythyroxine (Synthroid), the medication used to treat an underactive thyroid.
Interactions with your body. Your own body can react to drugs in unexpected ways. There is more than one version of each of the 50 or more CYP450 enzymes, and there is no easy or reliable way to identify which ones they have inherited. You may have reactions to certain medications because it breaks them faster or slower than most people. In addition, as we age, we tend to metabolize drugs more slowly, so that a lower than recommended dose can usually be sufficient. Kidney or liver disease can also slow down the rate at which drugs are metabolized. For these reasons, it is important to carefully monitor your reaction to any new medications you take.
Minimize risk of interactions
Dr. Phansalkar acknowledges that it is unrealistic to expect us to memorize every possible interaction for every medication we take. But the following can go a long way in reducing problems:
1. Know why you are taking each medication
Medication names are often difficult to pronounce, difficult to remember, and easy to mix. An error in listing your medications could mean that a potential interaction will go unnoticed. For example, Klonopin (the brand of clonazepam, used to treat panic attacks) may be mistaken for clonidine, a common blood pressure medication. However, if you tell a pharmacist or health care professional that you are taking Klonopin to lower your blood pressure, you will probably find that you are taking clonidine. Consider labeling each bottle or pack of pills with the reason you are taking the drug, for example, “blood pressure.”
2. Knowing how to take the medicine
It is important to know if you are taking your medicine with food or on an empty stomach. For example, taking a bisphosphonate (a class of drugs used to stop bone loss) with milk, coffee, or juice or eating anything within 30 minutes of taking the medication will void its effects. On the other hand, some medications are best taken with food, either to aid absorption or to prevent them from irritating the lining of the stomach. And some medications should not be taken with specific foods. For example, the antibiotic tetracycline should not be taken with dairy products because calcium interferes with the absorption of the drug.
3. Fill all your prescriptions at the same pharmacy
The health system remains fragmented. It is likely that your primary care team has a record of the prescriptions you got from that office, just like the specialists you have seen. However, each is not likely to know what others have prescribed. Although pharmacies store records of all the prescriptions they fill, one pharmacy may not have access to another’s records and therefore may not have a complete record of their drugs. Keeping an up-to-date list of your medicines would be very helpful, especially in emergency situations.
4. Be wary of supplements
Some of the more serious interactions between medications involve prescription drugs and supplements. Not only supplements are less likely than FDA-approved drugs to be listed in databases of drug interactions, but health care providers may also not know what supplements people are taking. Since there is not much evidence that supplements have health benefits, it is best to avoid them unless your doctor prescribes them.
5. Go easy on grapefruit juice
While it is true that grapefruit juice affects the metabolism of various medications, it usually takes about a quart of juice to make a difference. If you like juice, ask your pharmacist if any of the medicines you take are affected by it. If you are, you should still be able to enjoy half a grapefruit or a glass of 8 ounces of juice daily as long as you wait a few hours after taking the medication.
6. Limit Alcohol
It is not a good idea for women to have more than one drink a day in general, and it may be even worse to drink while taking drugs. Alcohol increases drowsiness, a desired effect of sleeping pills and a side effect of many antihistamines, antidepressants and anti-anxiety drugs. It can also irritate the lining of the esophagus and stomach, a special concern if you are taking aspirin, other nonsteroidal anti-inflammatory drugs, or an oral bisphosphonate for low bone density.
7. Talk to your pharmacist
When you pick up a prescription, you can find up to three different sheets or brochures with your drug, each detailing the conditions the drug is approved to treat, how to take the drug, and the possible side effects of the drug. If your first reaction is “too much information!” The next step should be to ask the pharmacist to summarize how to take the medicine and what to expect.
Pharmacists have a thorough understanding of how drugs work, their side effects, and the drugs, supplements, and foods with which they interact. In fact, you may want to bring all your prescription and over-the-counter medications, as well as any supplements you take, to the pharmacy when you pick up a new prescription. If the pharmacist identifies any possible interactions between your medications, he or she may suggest a schedule for taking them that will minimize the likelihood of interactions.
Your pharmacist may also be willing to talk to your health care team about how to adjust a dose of medication or find a better-functioning alternative. Some health plans have drug therapy treatment (MTM), or programs that allow an in-depth annual consultation with a pharmacist. Check yours to see if you qualify for MTM services.