EFFECTIVENESS OF CLOXACILLIN WITH AND WITHOUT GENTAMICIN IN SHORT-TERM THERAPY FOR RIGHT-SIDED STAPHYLOCOCCUS-AUREUS ENDOCARDITIS - A RANDOMIZED, CONTROLLED TRIAL

Background: It is often difficult to administer extended antibiotic th erapy in the hospital for right-sided Staphylococcus aureus endocardit is. 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-dru g therapy. Objective: To compare the efficacy of cloxacillin alone wit h that of cloxacillin plus gentamicin for the 2-week treatment of righ t-sided S. aureus endocarditis in intravenous drug users. Design: Open , randomized study. Setting: An academic tertiary care hospital in Bar celona, Spain. Patients: 90 consecutive intravenous drug users who had isolated tricuspid valve endocarditis caused by methicillin-susceptib le 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 exclusio n criterion. Intervention: Cloxacillin (2 g intravenously every 4 hour s for 14 days) alone or combined with gentamicin (1 mg/kg of body weig ht 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 analysi s of the efficacy subset, treatment was successful in 34 of the 38 pat ients 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 t wo in the combination therapy group. Of the 37 patients who completed 2-week treatment with cloxacillin, 34 (92%) were cured, and 3 (8%) nee ded 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 t he combination group had relapse. Conclusions: A penicillinase-resista nt penicillin used as single-agent therapy for 2 weeks was effective f or most patients with isolated tricuspid endocarditis caused by methic illin-susceptible S. aureus. Adding gentamicin did not appear to provi de any therapeutic advantages. Additional studies to confirm the thera peutic equivalence of short-course therapy with penicillinase-resistan t penicillin alone and therapy with combined regimens are warranted.