Experimental acute otitis media due to nontypeable Haemophilus influenzae: comparison of high and low azithromycin doses with placebo

Abstract

Treatment of acute otitis media (AOM) with azithromycin results in apparent clinical success, but tympanocentesis performed 4 to 6 days after initiation of therapy in children with nontypeable Haemophilus influenzae (NTHI) recovered from initial middle ear cultures demonstrates persistence of infection in more than 50% of episodes. We sought to determine the effect of azithromycin at different doses on the density of middle ear infection due to NTHI to provide additional understanding of this dichotomy between clinical and microbiologic outcome measures in AOM. In a chinchilla model of experimental otitis media (EOM), animals treated with placebo were compared to animals receiving a single daily dose 30 or 120 mg of azithromycin per kg of body weight per day for 5 days. Microbiologic outcome was assessed by obtaining quantitative cultures from the middle ear during a 5-day course and for 1 week following therapy. Azithromycin concentrations were measured to ascertain whether a concentration-dependent effect was present. Azithromycin at 30 and 120 mg/kg/day demonstrated a dose-dependent effect on the quantitative assessment of middle ear infection due to NTHI. A 30-mg/kg dose of azithromycin daily resulted in levels in serum and areas under the serum concentration-time curve at 24 h comparable to published data obtained with children given azithromycin at 5 to 10 mg/kg in multiday regimens. Increased doses of azithromycin (120 mg/kg) achieved 2.5- to 4-fold-higher levels in serum and 3- to 6-fold-higher total levels and levels in extracellular middle ear fluid as well as more rapid reduction in bacterial density and a greater proportion of middle ears with complete sterilization than either placebo or the 30-mg/kg/day regimen.

FIG. 1.

Microbiologic outcome in MEF of experimental AOM due to NTHI. Numbers above the bars are the numbers of infected ears over the total numbers of ears cultured (number of animals decreased due to deaths during the experiment; see the text). †, P < 0.002 treatment group versus the placebo group; ‡, P < 0.0001 120-mg/kg group versus the 30-mg/kg group.

FIG. 2.

Mean infection densities in EOM due to NTHI. Sterile ears were counted as having 10^0.7 CFU/ml, and the numbers of animals with sterile ears are identified at the bottom of the columns in the figure. †, P < 0.0001 treatment group versus the placebo group; ‡, P < 0.05 120-mg/kg group versus the 30-mg kg group.

FIG. 3.

Azithromycin concentrations in MEF in acute EOM. Total MEF was freeze-thawed to disrupt cells. The black bar indicates the duration of azithromycin therapy.