Higher dalbavancin exposure was associated with greater clinical success at day 70 among stabilized adults with complicated Staphylococcus aureus bacteremia, according to a prespecified secondary analysis of the DOTS randomized clinical trial.
The analysis included 97 patients assigned to dalbavancin who had at least one measurable postdose plasma concentration. All had achieved bloodstream clearance and clinical stabilization prior to randomization and received dalbavancin 1,500 mg intravenously on days 1 and 8, with dose adjustment for severe kidney impairment.
Among 93 patients evaluable for exposure-response analysis—those alive and free of infectious complications through day 22—72 (77%) achieved clinical success at day 70. Patients with total dalbavancin concentrations greater than 32 μg/mL at day 22 had higher success rates than those with concentrations of 32 μg/mL or less (97% vs 68%), corresponding to an adjusted difference of 25 percentage points. The estimate was imprecise, with a wide confidence interval.
The 32 μg/mL threshold was not prespecified. Investigators derived it through exploratory dichotomization of exposure data, and it requires external validation before clinical application.
The findings build on the parent DOTS trial, in which a 2-dose dalbavancin regimen was noninferior to standard intravenous therapy for completion of treatment in complicated S aureus bacteremia. Even patients with lower day 22 concentrations in the current analysis had outcomes numerically comparable to standard therapy in the parent trial.
Exposure Measures and Pharmacokinetics
In addition to day 22 concentration, researchers evaluated area under the concentration-time curve (AUC). Higher AUC values were also associated with improved outcomes, but these associations did not reach statistical significance in adjusted analyses.
Population pharmacokinetic modeling incorporated 640 plasma samples and identified creatinine clearance, body weight, albumin level, and age as key determinants of dalbavancin disposition. Clearance increased with kidney function, while distribution volumes scaled with body weight.
Dalbavancin demonstrated extensive protein binding. More than 90% of paired samples had an unbound fraction below 1%, and most unbound concentrations were below quantification by day 42. Associations between exposure and clinical success were stronger for total concentrations than for unbound measures, likely reflecting the narrow measurable range of unbound drug due to very high protein binding.
Safety
Serious adverse events occurred in 27% of patients with day 22 concentrations greater than 32 μg/mL and 43% of those with concentrations of 32 μg/mL or less. However, this difference was not statistically significant, and the study was not designed to assess safety differences across exposure levels.
Interpretation and Limitations
Because exposure was not randomized, the findings do not establish causality. Lower drug concentrations among patients with clinical failure may reflect differences in kidney function, body weight, albumin levels, or other sources of pharmacokinetic variability.
The analysis was restricted to patients who achieved bloodstream clearance and remained clinically stable through early follow-up, limiting generalizability to patients with early treatment failure or more severe illness.
Additional limitations include the exploratory use of dichotomization to define exposure thresholds and multiple comparisons, both of which increase the risk of spurious findings. Notably, nine patients with indeterminate outcomes were classified as failures under a worst-case approach, and all had day 22 concentrations of 32 μg/mL or less. Sensitivity analyses suggested the overall findings were robust to alternative assumptions.
Clinical Implications
The results suggest that sustained dalbavancin exposure may be important for preventing late complications of S aureus bacteremia and raise the possibility that some patients could benefit from additional dosing or exposure-guided strategies.
“These findings should be viewed as hypothesis generating and may inform future studies evaluating alternative dalbavancin dosing strategies,” wrote lead study author Thomas P. Lodise, PharmD, of Albany College of Pharmacy and Health Sciences, and colleagues.
Disclosures
The study was funded by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health, and study drug was provided by AbbVie. Several researchers reported financial relationships with pharmaceutical companies, including consulting fees, grants, and stock ownership. Full disclosures are available in the published study.
Source: JAMA Network Open
