A descriptive case series of the relationship between maintenance of conservative PK/PD efficacy thresholds of dalbavancin over time and clinical outcome in long-term treatment of staphylococcal osteoarticular infections.

Objective: To describe the relationship between maintenance of pharmacokinetic/pharmacodynamic (PK/PD) dalbavancin efficacy thresholds over time and clinical outcome in a case series of patients who underwent therapeutic drug monitoring (TDM) during long-term treatment of staphylococcal osteoarticular infections (OIs).

Methods: Patients who received two 1500-mg doses of dalbavancin 1 week apart for documented staphylococcal OIs, underwent TDM assessment, and had clinical outcome assessable at follow-up were included retrospectively. Dalbavancin concentrations ≥4.02 and/or ≥8.04 mg/L were identified as conservative PK/PD efficacy thresholds. The percentage of time of the overall treatment period with dalbavancin concentrations above these efficacy thresholds was calculated and correlated with clinical outcome.

Results: In total, 17 patients were included in this study. Long-term dalbavancin was used mainly for treating prosthetic joint infections (9/17, 52.9%). In 13/17 patients (76.5%), clinical outcome was assessable after at least 6 months of follow-up and was always successful (100.0%). In four of 17 patients (23.5%), clinical outcome is favourable after 3.7, 4.8, 5.1 and 5.3 months of follow-up, respectively. In most patients, both dalbavancin PK/PD efficacy thresholds were reached for most of the treatment period (%time ≥4.02 mg/L: 100% in 13 cases, 75-99.9% in two cases, 50-74.99% in two cases; %time ≥8.04 mg/L: 100% in eight cases, 75-99.9% in four cases, 50-74.99% in four cases, <50% in one case).

Conclusions: These findings could support the idea that maintenance of conservative PK/PD efficacy thresholds of dalbavancin for the majority of the treatment period may represent a valuable approach in dealing efficaciously with long-term treatment of staphylococcal OIs.