About
5 to 10 percent of adverse reactions to commonly used drugs are
allergic, which means that the patient's immune system overreacts to the
drug.
The most severe allergic reaction is anaphylaxis, which can result in
death. Symptoms of anaphylaxis include a sense of warmth, flushing,
itching, hives (which can occur alone, that is, without progression to
anaphylaxis), swelling in the throat, asthma or wheezing,
light-headedness from low blood pressure, irregular heart rhythm, nausea
or vomiting, abdominal cramping or shock.
These
symptoms require emergency attention. Most anaphylactic reactions occur
within one hour after the patient takes the drug but in up to 20 percent
of cases, the anaphylactic reaction may start up to several hours later.
Rarely,
blisters develop in association with a drug rash. This is a sign of a
serious complication, called erythema multiforme major (Steven-Johnsons
syndrome), and should immediately be reported to your physician. These
reactions can cause the skin to peel off and are treated like severe
burns.
It is very important to tell your doctor about any adverse reactions when you are taking a medication and to make certain that the doctor knows of any prior reaction to a drug being prescribed for you.