Patients allergic to penicillin at higher risk of C. difficile and MRSA infections : BMJ

The patients allergic to penicillin are at increased risk for Clostridium difficile and methicillin-resistant Staphylococcus aureus (MRSA) infections mediated by the increased use of β lactam alternative antibiotics, finds a study in The BMJ.

Kimberly G. Blumenthal, Division of Rheumatology, Allergy, and Immunology, Department of Medicine, Massachusetts General Hospital, Boston, MA, USA, and colleagues conducted the study to evaluate the relation between penicillin allergy and development of MRSA and C difficile.

For the study, the researchers used U.K. healthcare records to match roughly 64,000 adults with a documented penicillin allergy to nearly 240,000 penicillin users without a documented allergy (controls).

• During 6 years' follow-up, 0.7% of patients with penicillin allergy and 0.4% of controls developed a MRSA infection, and 0.7% and 0.5%, respectively, acquired C. difficile.


• Among patients with penicillin allergy the adjusted hazard ratio for MRSA was 1.69 (95% confidence interval 1.51 to 1.90) and for C difficile was 1.26 (1.12 to 1.40).


• The adjusted incidence rate ratios for antibiotic use among patients with penicillin allergy were 4.15 (95% confidence interval 4.12 to 4.17) for macrolides, 3.89 (3.66 to 4.12) for clindamycin, and 2.10 (2.08 to 2.13) for fluoroquinolones.


• Increased use of β lactam alternative antibiotics accounted for 55% of the increased risk of MRSA and 35% of the increased risk of C difficile.


• After multivariable adjustment, patients with penicillin allergy had nearly a 70% increased risk for MRSA and 30% increased the risk for C. difficile.

Infectious disease specialist Dr. Paul Sax comments, "This study adds to a substantial body of evidence that documents the harm associated with having a penicillin allergy, which limits antibiotic options. That the vast majority of people with a listed allergy to penicillin either have outgrown it or never had it at all makes taking a careful history (or referring for penicillin skin testing) a high priority in these patients."