Depomedrol multidose vials contain a bacteriostatic preservative that helps prevent infection or bacterial overgrowth. Benzyl alcohol is effective against both gram positive and gram negative organisms but myristyl-gamma picolinium chloride is ineffective against the gram negative serratia marcesens. Both multidose (benzyl alcohol) and single dose (MGPC) contain antimicrobial agents. The MGPC is mildly neurotoxic and the benzyl alcohol is moderate to severely neurotoxic. The alternative is use of multidose celestone but this contains benzylalkonium chloride, which is highly toxic to chondrocytes.
The CDC has taken a ridiculously hard line on multidose vial use that is not supported by scientific literature. Using a non-preservative containing solution such as Omnipaque along with new needle/new syringe for every access along with alcohol double wipe of the vial prior to accessing has prevented infection in my practice for the past 15 years. We use the vials for a month. Multidose vials should have no higher infection rate than the non-preservative containing vials, therefore using the measures taken above, there should be no cause for infection in the multidose vials. Because of the concern about serratia, found in some epidural abscesses, use of single dose vials for multiple uses may be questionable.
Diprovan is a potent growth media for bacteria due to the presence of a very weak antimicrobial, 0.005% disodium edetate, whereas the sodium metabisulfite containing Baxter formulation may be slightly better. The egg lecithin is one of the major growth media, something absent in Depomedrol. The MSDS Pfizer for depomedrol does not list bacterial growth characteristics and there is not much in the medical literature examining this either.
In retrospect, using non-preservative containing compounded drugs may be profoundly hazardous as was seen in the past with population infections due to contaminated depomedrol. Most compounding pharmacies today will not compound without preservatives, but will include MGPC in their compounded steroids, but call them "preservative free", an inaccuracy.
For more info, see Clinical neuromythology and other arguments and essays, by William Landau.