Background: It is often difficult to administer extended antibiotic therapy in the hospital for right-sided Staphylococcus aureus endocarditis. Although the effectiveness of single-drug therapy given for 4 to 6 weeks and that of two-drug therapy given for 2 weeks have been shown, no data are available on the effectiveness of short-course single-drug therapy.
Objective: To compare the efficacy of cloxacillin alone with that of cloxacillin plus gentamicin for the 2-week treatment of right-sided S. aureus endocarditis in intravenous drug users.
Design: Open, randomized study.
Setting: An academic tertiary care hospital in Barcelona, Spain.
Patients: 90 consecutive intravenous drug users who had isolated tricuspid valve endocarditis caused by methicillin-susceptible S. aureus, had no allergy to study medications, and had no systemic infectious complications that required prolonged therapy. An efficacy subset consisted of 74 of these patients who did not meet an exclusion criterion.
Intervention: Cloxacillin (2 g intravenously every 4 hours for 14 days) alone or combined with gentamicin (1 mg/kg of body weight intravenously every 8 hours for 7 days).
Measurements: Clinical or microbiological evidence of active infection after 2 weeks of therapy, relapse of staphylococcal infection, or death.
Results: In an analysis of the efficacy subset, treatment was successful in 34 of the 38 patients who received cloxacillin alone (89% [95% CI, 75% to 97%]) and 31 of the 36 patients who received cloxacillin plus gentamicin (86% [CI, 71% to 95%]). Three patients died: one in the cloxacillin group and two in the combination therapy group. Of the 37 patients who completed 2-week treatment with cloxacillin, 34 (92%) were cured, and 3 (8%) needed prolonged treatment to cure the infection. Of the 34 patients who completed 2-week treatment with cloxacillin plus gentamicin, 32 (94%) were cured and 2 (6%) required treatment for 4 weeks. One patient in the combination group had relapse.
Conclusions: A penicillinase-resistant penicillin used as single-agent therapy for 2 weeks was effective for most patients with isolated tricuspid endocarditis caused by methicillin-susceptible S. aureus. Adding gentamicin did not appear to provide any therapeutic advantages. Additional studies to confirm the therapeutic equivalence of short-course therapy with penicillinase-resistant penicillin alone and therapy with combined regimens are warranted.