Residual amount of vancomycin hydrochloride in vials after use.

We macroscopically observed vials of vancomycin hydrochloride (VCM) for injection (0.5 g/vial) dissolved in various solvents, and determined the presence or absence of residual VCM crystals. In addition, the residual VCM in vials after use was measured using a bioassay. In vials evaluated after use, the percentage of vials in which VCM crystals were macroscopically confirmed, the mean residual amount of VCM in the vials (residual %), and the percentage of vials with ≥50 mg (10 %) of residual VCM were 28.1 %, 15.0 ± 7.5 mg (3.0 %), and 0 %, respectively, after the dissolution of a single VCM vial in 10 ml of distilled water for injection (n = 57); 63.8 %, 30.2 ± 19.1 mg (6.0 %), and 16.1 %, respectively, after the dissolution of a single VCM vial in 100 ml of physiological saline (n = 224); and 72.2 %, 38.5 ± 28.0 mg (7.7 %), and 33.3 %, respectively, after the dissolution of two VCM vials in 100 ml of physiological saline (n = 18). The mean residual VCM amount was greater when using physiological saline than when using distilled water for injection as a solvent. These results show the need to follow the dissolution method described in the package insert, which calls for the addition of 10 ml of distilled water for injection to each 0.5 g VCM vial.