Drug-drug Interactions are a Leading Cause of Drug Reactions, and Growing Due to Polypharmacy
Because older adults often take more medications than younger adults, the number of adverse drug reactions increases with patient age. Adverse drug reactions, however, frequently go unnoticed or are misdiagnosed in older people for the following reasons:
- Drug reactions sometimes mimic signs or symptoms of disease (e.g., dementia).
- Symptoms of a drug reaction are thought to be caused by an existing medical condition or the onset of a new health problem.
- Physical reactions to medication, such as fatigue, falling, or weight loss, may be mistakenly labeled as "normal" aging.
There are many physical signs that may be attributed to an adverse drug reaction. These include:
- fatigue
- constipation or diarrhea
- confusion
- incontinence
- frequent falls
- depression
- weakness or tremors
- excess drowsiness or dizziness
- agitation or anxiety
- decreased sexual behavior
If a problem develops shortly after a person begins taking a new prescription drug, it is advisable to contact the prescribing doctor, or some other doctor, immediately. Beware that sometimes it takes more time for an adverse reaction to occur, making it less obvious to the patient that their medical "problem" might be an adverse reaction associated with one or more of their drugs.
One sub-set of adverse drug reactions that is growing in number is drug-drug interactions. Simply put, a drug-drug interaction occurs when the effect of one drug is altered by the presence of another drug in the body. For example:
- One drug might reduce or increase the effects of another drug.
- Two drugs taken together may produce a new and dangerous interaction.
- Two similar drugs taken together may produce an effect that is greater than would be expected from taking just one drug.
Polypharmacy -- which is generally defined as the use of at least three prescription drugs at the same time -- is on the rise in the U.S. for a variety of reasons, among them direct-to-consumer advertising and the mind-set that every ailment has a remedy in the form of a pill. When a person is taking several concomitant drugs, there is a higher risk of suffering an adverse drug reaction.
Some examples of how prescription drugs can interact with each other follow:
- Mixing antidiabetic medication (e.g., oral hypoglycemics) and beta blockers (e.g., Inderal) can result the decreased response of the antidiabetic drug and increased frequency and severity of low blood sugar episodes.
- Mixing antidiarrheal medication (e.g., Lomotil) and tranquilizers (e.g., Transxene, Valium), sedatives (e.g., Dalmane, Quaalude), or sleeping pills (e.g., Amytal, Nembutal, Seconal) can result in an increased effect of tranquilizers, sedatives, or sleeping pills.
- Mixing antihypertensive medication (e.g., Reserpine, Aldoril, Combipres) and digitalis (e.g., Lanoxin) can result in abnormal heart rhythms.
- Mixing anticoagulants (e.g., Coumadin, Warfarin) and sleeping pills (e.g., Nembutal, Amytal, Seconal) can result in decreased effectiveness of the anticoagulant medication.
In addition to prescription drugs interacting with each other, over-the-counter drugs can also interact with prescription drugs. Some examples of this type of drug interaction include:
- Aspirin can significantly increase the effect of blood thinning drugs (anticoagulants), thus increasing the risk of excessive bleeding.
- Antacids can cause blood-thinning drugs (anticoagulants) to be absorbed too slowly.
Antacids can interfere with drug absorption of antibiotics (i.e., tetracycline), thereby reducing the effectiveness of the drug in fighting infection. - Antihistamines, often used for allergies and colds, can increase the sedative effects of barbiturates, tranquilizers, and some prescription pain relievers.
- Decongestants in cold and cough medications can interact with diuretics or "water" pills to aggravate high blood pressure.
- Iron supplements taken with antibiotics can reduce or stop the ability of the antibiotics to fight infection. (The chemicals in the supplement and the antibiotic bind together in the stomach, instead of being absorbed into the bloodstream.)
- Salt substitutes can interact with "water" pills or blood pressure medication to increase blood potassium levels. This can result in symptoms of nausea, vomiting, muscle cramp diarrhea, muscle weakness, and cardiac arrest.
These are just a few of the many interactions that can occur when multiple drugs are taken together. Accordingly, it is very important that a patient check with their prescribing doctor(s) and dispensing pharmacist(s) to make sure that the combination of drugs prescribed to them does not have the potential to interact so as to cause them to suffer an adverse drug reaction.
(Posted by: Tom Lamb)