Drugs have to be absorbed into the blood stream to be effective. Once in the blood, they are transported by protein carriers throughout the body. Some drugs act on specific areas, while others affect the whole body. Drugs are eliminated from the body by the liver or kidneys.
When people talk about drug interactions they are usually referring to drugs that interfere with the effects of other drugs. In reality, there are several types of drug interactions. And while most people know about drug-drug interactions, interactions involving drugs and diseases and drugs and food are less well known-and just as important.
Two drugs taken at the same time can influence how each drug works. Drug interactions sometimes occur in the stomach. For example, taking calcium at the same time as some antibiotics (say, tetracycline) can inactivate the antibiotic. Or, certain drugs can impair the stomach's ability to empty, causing other drugs to be absorbed too quickly or too slowly. Some drugs impair the liver or the kidney's ability to eliminate certain drugs, thus modifying the duration of action of other drugs. Fortunately, not all drug-drug interactions have a negative impact. Some interactions can actually benefit the person. For instance, the impact of one drug on another can be used to reduce one of the drug's side effects, as happens with certain antihypertensives.
People react differently to the same drug: age, weight, heredity, and health status are all factors that affect the way a person will respond to a particular drug.
A person's health status may influence how a drug behaves in the system. For example, when a migraine sufferer takes an analgesic to combat the pain, the analgesic may take longer to reach its maximal effect because a migraine attack causes the stomach to empty more slowly. As a result, relief is delayed. Thus, there is an interaction between the disease (migraine) and the drug used to treat it (analgesic). Diarrhea is another example. When a drug passes through the intestine too quickly (as in diarrhea), it may not have enough time to be fully absorbed before being eliminated from the system. As a result, the drug may not have a chance to achieve its full effect.
Another example of drug-disease interaction can occur among people with impaired liver or kidney function, which decreases the ability of these organs to eliminate certain drugs from their system. In these cases, the drug stays in the body longer than normal, building up and causing side effects. To avoid this, these people often have to take smaller doses or space the doses farther apart.
Some drugs affect our sense of taste, causing loss of appetite or feelings of nausea. Others reduce the absorption of certain vitamins. Some food-drug or alcohol-drug interactions have very serious consequences.
Preventing drug interactions
While some drug interactions are easy to prevent, others are difficult to anticipate. Numerous factors are involved. Here's what you can do:
- Avoid frequently switching health-care providers to lessen the possibility of conflicting drug therapies;
- Keep your health-care provider informed about what medication(s) (prescription and non-prescription drugs and natural health products) you are taking. Keep a up to date record of them and bring it with you when you go on any medical appointment;
- Use the same pharmacy for all your medications, so your pharmacist can monitor your various drug therapies (and prevent possible conflict);
- Check with your physician or pharmacist before taking any natural health products or non-prescription drugs;
- Ask your pharmacist or doctor what you need to avoid when you are prescribed a new medication;
- Keep medications in their original containers so that you can easily identify them.
Following these suggestions will allow your health-care providers to do their job properly and help prevent unwanted drug interactions.
Drug interactions and the elderly
Drug interactions affect the elderly more than younger people because the elderly are more likely to suffer from chronic diseases requiring medication, such as diabetes, hypertension, and respiratory problems, and also more likely to have impaired liver or kidney function.