JT is a 58-year-old women who is on vancomycin empirically for pyomyositis confirmed by MRI. Surgical debridement has successfully removed infected…

The patient has a confirmed methicillin-sensitive Staphylococcus aureus (MSSA) infection. The first-line treatment for serious MSSA infections is an anti-staphylococcal penicillin (e.g., oxacillin) or a first-generation cephalosporin (e.g., cefazolin). Given the patient's non-severe penicillin allergy (rash) and documented prior tolerance of a cephalosporin, the risk of cross-reactivity is extremely low. Cefazolin is the most appropriate choice as it provides targeted, narrow-spectrum bactericidal therapy, adhering to principles of antimicrobial stewardship by de-escalating from broad-spectrum vancomycin.

A. Oxacillin: This is an anti-staphylococcal penicillin and would be a first-line choice, but it is inappropriate due to the patient's documented penicillin allergy.
B. Doxycycline: This agent is generally bacteriostatic and not preferred for treating severe, deep-seated bactericidal infections like pyomyositis when more effective options are available.
C. Ceftaroline: This is a fifth-generation cephalosporin with MRSA activity. Its use for a confirmed MSSA infection is unnecessarily broad-spectrum and poor antimicrobial stewardship.
D. Daptomycin: This agent is also unnecessarily broad for MSSA. It is typically reserved for MRSA or cases of severe, anaphylactic beta-lactam allergies.

1. Liu

C.

Bayer

A.

Cosgrove

S. E.

et al. (2011). Clinical practice guidelines by the Infectious Diseases Society of America for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children. Clinical Infectious Diseases

52(3)

e18–e55. Section: "What is the preferred therapy for invasive MSSA infections?"

Recommendation 1. The guideline states

"For patients with invasive MSSA infections

a β-lactam antibiotic is the agent of choice... Cefazolin is an alternative for patients with a history of a mild

non-IgE-mediated reaction to penicillin." https://doi.org/10.1093/cid/ciq146

2. DiPiro

J. T.

Yee

G. C.

Posey

L. M.

Haines

S. T.

Nolin

T. D.

& Ellingrod

V. (2020). Pharmacotherapy: A Pathophysiologic Approach (11th ed.). McGraw-Hill Education. Chapter 93

"Bone and Joint Infections." This chapter identifies nafcillin

oxacillin

or cefazolin as the drugs of choice for MSSA osteomyelitis

a similar deep-seated infection.

3. Picard

M.

Robitaille

G.

Karam

F.

et al. (2019). Cross-reactivity to cephalosporins and carbapenems in penicillin-allergic patients: two systematic reviews and meta-analyses. The Journal of Allergy and Clinical Immunology: In Practice

7(8)

2722–2738.e5. This meta-analysis supports the low risk (<1%) of cross-reactivity between penicillins and first-generation cephalosporins in patients with non-severe penicillin allergies. https://doi.org/10.1016/j.jaip.2019.05.038