Methods: This is a single center, retrospective chart evaluation of systemic MSSA infections treated with nafcillin or cefazolin. Inclusion criteria: admitted to UC Davis Medical Center between 7/1/2011 – 7/1/2015, ≥18 years of age, ≥1 MSSA culture, receipt of cefazolin or nafcillin, planned treatment ≥2 weeks. Clinical outcomes and tolerability of each antibiotic was assessed. Endocarditis patients were excluded from clinical outcome analysis as cefazolin is not first line therapy per IDSA guideline. Clinical failures: death due to MSSA infection, antibiotic therapy change due to clinical failure, or relapse.
Results: 80 patients were included, 50 in the nafcillin arm, 30 in the cefazolin arm. 11 patients (22%) were excluded from nafcillin clinical outcome analysis (7 endocarditis; 4 inadequate records), 2 patients (6.7%) were excluded from the cefazolin clinical outcome analysis (1 endocarditis; 1 inadequate record). The clinical cure rates were similar between the two groups, 97% (38/39) vs 96% (27/28). 9 hypokalemia, 2 rash, 3 IN, 4 neutropenia episodes occurred in the nafcillin arm, and 3 rashes in the cefazolin arm. Significantly more nafcillin patients experienced an ADR, 34% (18/50) vs 10% (3/30), P = 0.038. Nafcillin patients also experienced more moderate or severe ADRs, 26% (13/50) vs 3.3% (1/30), P = 0.013. Changes in therapy due to ADRs were similar between the groups (14% vs 10%, P = 0.73). A higher percentage of nafcillin patients required medical intervention related to the ADR (24% vs 10%, P = 0.14). All patients with hypokalemia were managed without therapy change.
Conclusion: Nafcillin and cefazolin had comparable cure rates for MSSA infections, but nafcillin had significantly more ADRs. The incidence and severity of antimicrobial adverse effects should be considered in addition to clinical success rates when choosing treatment for MSSA infection.
S. H. Cohen, None
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