Symptoms

Signs and symptoms of penicillin allergy often occur within an hour after taking the drug. Less commonly, reactions can occur hours, days or weeks later.

Penicillin allergy signs and symptoms may include:

• Skin rash
• Hives
• Itching
• Fever
• Swelling
• Shortness of breath
• Wheezing
• Runny nose
• Itchy, watery eyes
• Anaphylaxis

Anaphylaxis

Anaphylaxis is a rare, life-threatening allergic reaction that causes the widespread dysfunction of body systems. Signs and symptoms of anaphylaxis include:

• Tightening of the airways and throat, causing trouble breathing
• Nausea or abdominal cramps
• Vomiting or diarrhea
• Dizziness or lightheadedness
• Weak, rapid pulse
• Drop in blood pressure
• Seizures
• Loss of consciousness

Delayed reactions resulting from penicillin allergy

Less-common penicillin allergy reactions occur days or weeks after exposure to the drug and may persist for some time after you stop taking it. 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 signs and symptoms
• Drug reaction with eosinophilia and systemic symptoms (DRESS), which results in rash, high white blood cell counts, general swelling, swollen lymph nodes and recurrence of dormant hepatitis infection
• Stevens-Johnson syndrome or toxic epidermal necrolysis, which involves severe blistering and peeling of the skin
• Inflammation in the kidneys (nephritis), which can cause fever, blood in the urine, general swelling, confusion, and other signs and symptoms

Adverse events that are not allergic reactions

You may experience side effects of penicillin — as happens with other medications — that are not an allergic reaction to the drug. Depending on the type of penicillin, common side effects may include mild nausea or diarrhea, headache, or vaginal itching. Signs or symptoms of an infection for which you are being treated — or unrelated symptoms — also may be mistaken as an allergic drug reaction.

When to see a doctor

See your doctor as soon as possible if you experience signs or symptoms of penicillin allergy. It's important to understand and discuss what is an allergic reaction, what is a typical side effect and what you can tolerate in taking a medication.

Call 911 or emergency medical help if you experience signs of a severe reaction or suspected anaphylaxis after taking penicillin.