Nonpruritic, nonurticarial rashes occur in up to 10% of patients receiving penicillins. These rashes are usually not allergic and are not a contraindication to the use of a different beta-lactam

The frequently cited risk of 8 to 10% cross-reactivity between penicillins and cephalosporins is an overestimate based on studies from the 1970’s that are now considered flawed

• Expect new intolerances (i.e. any allergy or adverse reaction reported in a drug allergy field) to be reported after 0.5 to 4% of all antimicrobial courses depending on the gender and specific antimicrobial
• Expect a higher incidence of new intolerances in patients with three or more prior medication intolerances

• For type-1 immediate hypersensitivity reactions (IgE-mediated), cross-reactivity among penicillins is expected due to similar core structure and/or major/minor antigenic determinants, use not recommended without desensitization

• For type-1 immediate hypersensitivity reactions, cross-reactivity between penicillins and cephalosporins is due to similarities in the side chains; risk of cross-reactivity will only be significant between penicillins and cephalosporins with similar side chains

• Only type-1 immediate hypersensitivity to a penicillin manifesting as anaphylaxis, bronchospasm, angioedema, hypotension, urticaria or pruritic rash warrant the avoidance of cephalosporins with similar side chains and other penicillins

• Patients with type-1 immediate hypersensitivity to a penicillin may be safely given cephalosporins with side chains unrelated to the offending agent

  • For example, ceFAZolin does not share a side chain with any beta-lactam and is not expected to cross react with other agents

• Cross-reactivity between cephalosporins is low due to the heterogeneity between side chains; therefore, a patient with a cephalosporin allergy may be prescribed another cephalosporin with a dissimilar side chain

• Cross-reactivity between penicillins and carbapenems is low. Carbapenems would be a reasonable option when antibiotics are required in patients with type-1 immediate hypersensitivity reaction to penicillins

• Any patient with possibility of type-1 immediate hypersensitivity to a beta-lactam should be referred for allergy confirmation

Patients with one of the following reactions secondary to beta-lactam use should avoid beta-lactams and not receive beta-lactam skin testing, re-challenging or desensitization:

• Stevens-Johnson syndrome

• toxic epidermal necrolysis

• drug reaction with eosinophilia and systemic symptoms

• immune hepatitis

• hemolytic anemia

• serum sickness or

• interstitial nephritis