What can physicians tell patients about the shelf life of antimicrobial ear drops and when bottles might become contaminated after use in the infected ear canal?
Background: Little evidence exists regarding the shelf life of antimicrobial ear drops after opening or when patients should discard the bottle. Additionnally, little is known about contamination after use in the infected ear.
Explore this issue:March 2010
Study Design: A prospective experimental design over a four-month period. Agar plates inoculated with both Staphylococcus aureus and Pseudomonas aeruginosa were used to assess effectiveness of ear drops containing gentamicin and ciprofloxacin. Bottles were assessed for contamination once opened, and drops used for one week on patients with otorrhea were analyzed for contamination.
Setting: Vancouver, British Columbia, Canada
Synopsis: The antibiotic drops remained effective over the four-month testing period without significant reduction in the zone of inhibition measured on the inoculated agar plates. None of the unused bottles of drops became contaminated. All of the patient ear cultures were positive, but neither the bottle tip cultures nor the bottle content samples grew organisms. One limitation was that only two ear drops were analyzed. However, the two drops studied were effective against the most common microorganisms. The study did not try to differentiate between those patients with otitis externa or media, or those with granular myringitis, but instead concentrated on the symptom of otorrhea, which is common to all.
Bottom Line: Patients can keep antimicrobial ear drops for up to four months at least, for use in treating subsequent episodes of otorrhea.
Citation: Clark MP, Pangilinan L, Wang A, et al. The shelf life of antimicrobial ear drops. Laryngoscope. 2010;120(3):566-570.