Sunday, January 15, 2006

drug reactions, adverse

Adverse drug reactions occur more frequently in the elderly. In one survey, 15.4 percent of hospitalized patients over age 65 suffered reactions compared to 6.3% of those patients under age 60. This higher incidence in the elderly may be due to a greater use of drugs in this age group, increased sensitivity to drug effects, impaired homeostatic mechanisms (steady state of body functions) and decreases in renal (kidney) and hepatic (liver) function.
Adverse reactions may be classified as
pharmacologic, allergic, or idiosyncratic. Toxicity occurs from over-dosage but can also be present in an elderly patient on normal dosages because of increased sensitivity to drugs as well as decreased renal and hepatic elimination. Another pharmacologic reaction is that of side effects, the undesirable secondary actions that are inseparable from the desired action of the drug. For example, the induced sedation that occurs from the use of antihistamines is a generally unwanted side effect. Both the toxic effects and the side effects can be minimized with reduction in the dosage.
Allergic reactions are the result of antigen-antibody interaction (the process in which white blood cells produce substances to respond to a foreign body) and require prior exposure to the antigenic agent (drug). Reactions range from a mild rash to anaphylaxis (severe reaction resulting in swelling and even shock) and death. Careful documentation of previous drug experiences will help avoid such medication in the future. Health-care personnel should be prepared for the necessity of resuscitation. Idiosyncratic reactions are rare, unpredictable, often severe, and are not related to dosage. Drugs that precipitate hemolysis (breakdown of red blood cells) in glucose- 6-phosphate dehydrogenase deficiencies (such as primaquine) and acute intermittent porphyria (barbituates) are examples of idiosyncratic reaction.
To prevent such adverse reactions, several precautions should be followed. A careful history of current medications and past medication experiences is necessary so that repetition of bad reactions can be avoided. Patients at greatest risk, including the elderly and those with impaired renal function, should be started at lower dosages that can be gradually increased as tolerance is determined. It is also necessary to be aware of possible toxic reactions associated with a particular drug.
The most significant way to prevent adverse reactions is to avoid unnecessary drug exposure. Prescriptions should be limited to only those instances where drug therapy is clearly indicated and should be discontinued as soon as possible.
Covington, T., and Walker, J. Current Geriatric Therapy. Philadelphia: W. B. Saunders, 1984.

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