Viability of selected microorganisms in non-cytotoxic aseptic preparations

Introduction

Numerous ready-to-use parenteral solutions are aseptically prepared in pharmacy-based aseptic preparation units. The aim of the study was to evaluate the ability of four different pathogens related to hospital infections to grow in ready-to-use solutions typically prepared in hospital pharmacies.

Method

In four consecutive series the antimicrobial activity of the following products was tested caspofungin 35 mg or 70 mg/250 mL 0.9 % NaCl solution (NS), micafungin 1 mg/mL in NS, vancomycin 5 mg/ml in G5/G10, heparin-sodium 1 IE/mL, epinephrine 0.02 mg/mL in G5, norepinephrine 1 mg/mL in G5, phenylephrine 10 mg/mL, 0.8 molar KCl solution, insulin 1 I.U./mL in G5/G10, midazolam 5 mg/mL injection, tranexamic acid injection solution 100 mg/mL, 50% glucose solution, SMOF Lipid 20% lipid emulsion, 1% propofol injection. 9 mL aliquots of each test solution were inoculated with 1 mL suspension of selected strains, i.e. S. aureus, P. aeruginosa, E. faecium or C. albicans. The inoculated solutions were stored at 22 °C, samples taken in predefined intervals from 0 to 144 hours and transferred to tryptic soy agar plates. The plates were incubated at 37 °C and colony forming units counted after 24 hours.

Results

Selected strains lost viability in preparations containing vancomycin, phenylephrine or midazolam after a period of a few hours or days. Caspofungin and micafungin exhibited antifungal activity. Glucose 50% w/v solution generated antimicrobial activity against P. aeruginosa and C. albicans immediately after inoculation. In tranexamic acid solutions only P. aeruginosa lost viability after 48 h of inoculation. In the lipid containing emulsions (propofol, SMOF Lipid) CFUs increased rapidly.

Discussion

Most of the tested preparations induced no or merely species-specific growth inhibition of the tested organisms. The antimicrobial activity of vancomycin, caspofungin, and micafungin confirmed the validity of the experiments. Low pH values and high osmolality are most probably the reason for growth inhibition in midazolam solutions and 50% glucose solution, respectively. The antimicrobial activity of phenylephrine solutions is caused by the excipient sodium metabisulfite.

Conclusion

The insufficient antimicrobial properties of ready-to-use solutions should be considered while determining the shelf-life of the products. Ready-to-use preparations, especially fat emulsions should be kept refrigerated whenever possible to inhibit the multiplication of any contaminating organism.