It is unwise to give penicillins to patients who have a history of definite and moderate to severe allergy to penicillin. It may be unavoidable in some situations e.g., enterococcal endocarditis or Listeriosis. These patients need a desensitization protocol. Please consult the Infectious Diseases Physician or Clinical Immunologist.
Many patients who are said to have penicillin allergy do not in fact have a true allergy. Vomiting, loose motions and other vague symptoms do not represent allergy. An erythematous skin rash represents a mild allergy and is not likely to cause problems. Cephalosporins are usually safe in these patients.
If there is a history of severe allergy e.g., urticaria, hypotension, or collapse, penicillins should not be given if there is an alternative. The risk of a reaction to cephalosporins in these patients is small - probably less than 5%. Nevertheless other agents may be available and should be used in preference.