Symptoms of a serious drug allergy often occur within an hour after taking a drug. Other reactions, particularly rashes, can occur hours, days or weeks later. Drug allergy symptoms may include:  Skin rash Hives Itching Fever Swelling Shortness of breath Wheezing Runny nose Itchy, watery eyes  Anaphylaxis Anaphylaxis is a rare, life-threatening reaction to a drug allergy that causes the widespread dysfunction of body systems. Symptoms of anaphylaxis include:  Tightening of the airways and throat, causing trouble breathing Nausea or abdominal cramps Vomiting or diarrhea Dizziness or lightheadedness Weak, fast pulse Drop in blood pressure Seizure Loss of consciousness  Other conditions resulting from drug allergy Less-common drug allergy reactions happen days or weeks after exposure to a drug and may persist for some time after you stop taking the drug. These conditions include:  Serum sickness, which may cause fever, joint pain, rash, swelling and nausea Drug-induced anemia, a reduction in red blood cells, which can cause fatigue, irregular heartbeats, shortness of breath and other symptoms Drug rash with eosinophilia and systemic symptoms (DRESS), which results in rash, high white blood cell count, general swelling, swollen lymph nodes and recurrence of dormant hepatitis infection Inflammation in the kidneys, also called nephritis, which can cause fever, blood in the urine, general swelling, confusion and other symptoms 
symptoms drug allergy occur hour taking drug  reactions  rashes  can occur hours  days weeks later  drug allergy symptoms may include:  skin rash hives itching fever swelling shortness breath wheezing runny nose itchy  watery eyes  anaphylaxis anaphylaxis rare  life-threatening reaction drug allergy causes widespread dysfunction body systems  symptoms anaphylaxis include:  tightening airways throat  causing trouble breathing nausea abdominal cramps vomiting diarrhea dizziness lightheadedness weak  fast pulse drop blood pressure seizure loss consciousness  conditions resulting drug allergy less-common drug allergy reactions happen days weeks exposure drug may persist time taking drug  conditions include:  serum sickness  may cause fever  joint pain  rash  swelling nausea drug-induced anemia  reduction red blood cells  can cause fatigue  irregular heartbeats  shortness breath symptoms drug rash eosinophilia systemic symptoms (dress)  results rash  high white blood cell count  general swelling  swollen lymph nodes recurrence dormant hepatitis infection inflammation kidneys  called nephritis  can cause fever  blood urine  general swelling  confusion symptoms 
drug allergy