Diffusion of amoxicillin into heart valves from infective endocarditis patients

Amoxicillin is the drug of choice in the management of streptococcal and enterococcal infective endocarditis (IE) but little is known regarding amoxicillin diffusion into infected heart valves. Herein, we assessed amoxicillin valvular distribution and related pharmacokinetic/pharmacodynamic (PK/PD) target attainment in IE patients undergoing heart valve surgery.

In this 2-year prospective study, patients with IE treated by continuous infusion of amoxicillin and undergoing a surgical valve replacement were included. Both amoxicillin plasma and tissue concentrations were measured the day of surgery. Amoxicillin concentration in plasma and crushed heart valves were measured by a validated liquid chromatography method coupled with ultra-violet and tandem mass spectrometry, respectively. MIC and MBC of amoxicillin were determined for all available isolates. The rate of achievement of PK/PD efficacy parameters were assessed.

Twenty-two heart valves were removed from 20 patients. Bacterial aetiology was streptococcal (n = 17) and enterococcal (n = 3). Amoxicillin mean daily dose was 12 ± 3 g/24 h, mean plasma concentration was 29 ± 21 mg/L (n = 15), mean tissue concentration was 23 ± 15 mg/L (n = 22). Median diffusion rate was 62%. Patients reached a plasma concentration target >4XCMI (n = 13). Tissue concentrations were bactericidal for all streptococcal IE but not for enterococcal IE.

Amoxicillin intravalvular measurements in IE treated patients showed significant penetration into the infectious site. These data are reassuring that in situ bactericidal concentrations can be largely achieved in the management of streptococcal IE and support the need for combination antibiotic therapy for enterococcal IE.