Duration of antibacterial effectiveness of gentamicin ear drops in external otitis.

The recommendation of Anderson and Steele, for the use of ear drops four times a day, has not been changed since 1948. In order to re-evaluate the frequency of using ear drops, we examined the duration of the effectiveness of the antibacterial activity of gentamicin ear drops in external otitis. Seventeen patients (25 ears) with external otitis were studied. We took 18 samples from each ear at 0, 1, 2, 3, 6, 8, 10, 12 and 14 hours and measured the concentration of gentamicin on the wick and in the ear canal. We found that the concentration of gentamicin began to decrease only after 12 hours and a more significant decrease was detected after 14 hours of treatment. We have shown that the antibiotic used on the wick is effective for 12 hours. In conclusion, we recommend using ear drops twice a day on a wick as routine therapy for external otitis.