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
