Penicillin allergy and Cephalosporin cross-reactivity

1. Penicillin Allergy:

1-10% of pts show adverse drug rxns (ADR).

Anaphylaxis=0.1%

Ampicillin-induced rash=10%

Only 10-20% of pts allergic to pen have (+) skin test

80-90% of pen ADRs occur 3 days-weeks after exposure (ie. stomach cramps & diarrhea)

2. Cephalosporins: (dentists are surprisingly using this more and more

because it’s a broad spectrum AB).

Estimated 15% of pts receiving this class show cross allergy with

penicillins and vice versa.

Cross Reactivity in Pen Allergic Pts:

1. the more structurally dissimilar two agents are, the less likely there will be cross reactivity (sensitivity).

2. Third generation Cephalosporins less likely to cause allergic response in penicillin sensitive pts compared to first generation cephalosporins.

3. Imipen and aztreonam are rarely used by dentists… don’t worry about these

4. Rarely, some pts show cross-allergic rxns to all ABs. Such pts are usually pan allergic (latex, foods, etc.).

Category: Pharmacology Notes