The aim of this study was to investigate the activity of dalbavancin against MRSA and MRSE growing in biofilms. The advantages of dalbavancin include its weekly dosing regimen and its high efficacy against gram-positive prokaryotes. In a study published by Raad et al., the efficacy of dalbavancin (one biweekly dose) compared with a 14-day course of vancomycin (twice a day) in patients with catheter-related bloodstream infection was evaluated [
8]. The study showed dalbavancin to have a higher overall success rate compared to vancomycin. As a result it was hypothesized that due to the high plasma concentrations of dalbavancin, its penetration into biofilms could be significantly higher than that of vancomycin. However, until this point, in-vitro activity of dalbavancin against biofilms has not been evaluated [
8]. From the results of this study, dalbavancin shows in-vitro activity against biofilms with MRSA and MRSE in concentrations between 1 and 16 mg/l, which are concentrations easily reached in vivo, as mean plasma concentrations have been shown to be > 35 mg/l for 7 days after one dose of 1,000 mg [
6]. Another study conducted by Baldoni et al. investigated the activity of dalbavancin against planktonic and biofilm MRSA in a foreign-body infection model in guinea pigs. Dalbavancin led to a reduction of planktonic MRSA in cage fluid, but failed to eradicate biofilm MRSA from cages [
7]. Only when dalbavancin was combined with rifampicin could reduction of biofilm MRSA be observed [
7]. We suspect this finding to be due to higher protein binding in the in-vivo model, as the intraperitoneally applied concentrations of dalbavancin resemble the concentrations used in our in-vitro model [
7]. Furthermore, metabolic processes after intraperitoneal application play a crucial role in the in-vivo model. Despite the advantages of subcutaneous animal foreign body models, they also have some limitations. In pharmacokinetic studies, differences in metabolic processes in small animals compared to humans have to be taken into account [
11]. To further understand these findings, foreign body models with intravenous application of dalbavancin are needed. Focusing on in-vitro effects of dalbavancin, we observed previously undescribed properties of this antimicrobial agent. In the test runs performed prior to our experiment, we dissolved 500 mg of dalbavancin in 25 ml aqua bidestillata and 5% glucose (50 mg/ml) as described in the package information leaflet, and performed the same biofilm assay as described above; however, no reduction of biofilm could be observed. The OD
650 was even higher in the wells filled with the highest dalbavancin concentrations, which made us revise our method. Comparing our results of dalbavancin in TSB with our pretests of dalbavancin in glucose, we concluded that in-vitro biofilm growth of MRSA and MRSE might be enhanced by glucose even when combined with dalbavancin. This effect is very likely to apply to the in-vitro model only, as glucose is metabolized in vivo after intravenous administration. We conclude that dalbavancin successfully reduced biofilms in vitro at concentrations which can be easily obtained in vivo, which substantiates the previously published findings that dalbavancin might have considerable potential as a drug in medical device infections, for which it is currently not approved [
6]. In conclusion, because of the activity of dalbavancin on MRSA and MRSE biofilms demonstrated in this study, we recommend further studies on the activity and efficacy of dalbavancin in in-vivo models with medical device associated infections, as a biweekly dosing regimen could not only reduce healthcare costs, but also improve patients’ quality of life.