Use of high-performance liquid chromatography (HPLC) to monitor β-lactam plasma concentrations during the treatment of endocarditis

Guidelines recommend high doses of β-lactams for the therapy of endocarditis. This report describes a retrospective study of 15 endocarditis patients (median age 64 years), treated according to guidelines, whose β-lactam trough plasma concentrations were measured with high-performance liquid chromatography because of tolerance or efficacy concerns. For amoxycillin, the mean level was 86.8 mg/L (range: 30-212 mg/L); five (45%) patients had concentrations > 1000× MIC. For cloxacillin, the mean level was 47.9 mg/L (range: 16.7-104 mg/L). The consequences of high and unpredicted β-lactam trough plasma concentrations for a prolonged period have not yet been thoroughly evaluated.