Signs and symptoms of a penicillin allergy include hives, rash and itching as well as shortness of breath and wheezing, states Mayo Clinic. Runny nose; itchy, watery eyes; swelling; and fever may also occur. A person who is allergic to penicillin is likely to experience an allergic reaction within an hour of taking the medication.
Anaphylaxis is a rare but serious allergic reaction that can cause breathing difficulty due to airway tightening, notes Mayo Clinic. The individual may feel dizzy; have a weak, rapid pulse and low blood pressure; and lose consciousness or have seizures. Abdominal cramps, nausea, vomiting and diarrhea may occur. Anaphylaxis requires immediate medical attention.
Certain allergic reactions to penicillin, such as anemia and kidney inflammation, may not develop for days or weeks after taking the drug, and the effects may be long-lasting, according to Mayo Clinic. Serum sickness, causing fever, painful joints, rash, swelling and nausea, is another possible reaction to penicillin. Drug reaction with eosinophilia and systemic symptoms may also occur. This involves elevated white blood cell counts, swollen lymph nodes, rash, generalized swelling and a flareup of a previously dormant hepatitis infection.
People are more likely to have a severe allergic reaction to penicillin if they've had an anaphylactic reaction to the drug in the past, notes WebMD. They are also more susceptible to a severe reaction if they have tested positive for a penicillin allergy or developed hives shortly after taking the drug.