Antibacterial properties of additives used in injection immunotherapy

Previous studies have reviewed the safety of preparing and administering allergy injection immunotherapy in a physician's office, and showed no evidence of infectious complications. The current study examines the antimicrobial properties of the common additives used in preparation of multidose immunotherapy vials.

Vials were prepared with varying concentrations of glycerin (0-25%), phenol (0-0.4%) and combinations of glycerin with phenol. A standard inoculum of Staphylococcus aureus was introduced in each vial and incubated. Optical densities were measured and colony counts were performed at 24 and 48 hours. Follow-up broth microdilution assays were performed using varying inocula of bacteria and the highest concentrations of additives to determine the number of bacteria for which these solutions were bacteriostatic and/or bactericidal. Optical densities were measured and colony counts were performed as in the vial assays.

All vials with varying dilutions of glycerin, phenol, and their combination showed bacterial growth with the standard inoculum of Staphylococcus aureus. Visible turbidity and optical density were inversely related to additive concentration. Follow-up microdilution assays with differing concentrations of bacteria demonstrated bactericidal activity with inocula of 1 × 10(3) colony forming units (CFU) of Staphylococcus aureus at clinically used concentrations of glycerin and phenol.

Higher concentrations of additives show better inhibition of bacterial growth. Solutions containing glycerin showed superior bactericidal activity than those containing only phenol. At concentrations of additives used in preparing allergy immunotherapy vials, antibacterial effects were observed with inoculation of 1 × 10(3) CFU or less of Staphylococcus aureus.