Objectives: To demonstrate the efficacy and safety of an antibiotic ear drop formulation combining polymyxin B sulfate, neomycin sulfate and gramicidin (PS) in patients with acute bacterial otitis externa (AOE). The combination was compared to glycerol ear drops, a non-pharmacologic treatment of AOE.
Methods: An active controlled, double-blind, randomized, parallel group, multicenter clinical trial study design was performed in ear, nose and throat (ENT) practices with a planned interim analysis for sample size adaptation. In total, 244 patients aged 19-84 with no previous episode of otitis externa within the last year were randomized to receive either PS or glycerol ear drops thrice daily for 10 ± 2 days.
Outcome measures: Absolute change in the clinical symptom score (CSS) (with subscores redness, swelling, pain, and secretion) from Day 1 to 4 was measured. As second endpoints, absolute change in CSS, individual subscores, pain perception measured on a visual analog scale (VAS) and intake of paracetamol 500 mg tablets were noted. Moreover, patient's assessment of efficacy at Day 10 and the frequency and type of adverse events were noted.
Results: On Day 4, the CSS showed a clear advantage for the PS group over the glycerol group, being lower by 0.6 (p < 0.03); the clinical outcome was even more pronounced after 10 days (p = 0.006). The swelling subscore showed a statistically significant difference favoring the PS treatment group in Days 1-4 (p = 0.01) and Days 1-10 (p = 0.003). More PS- than glycerol-receiving patients rated the efficacy as good (glycerol: 32%; PS: 36%) or very good (glycerol: 38%; PS: 48%). Males, patients with AOE for >2 days and those with positive microbiologic findings profited most from PS therapy.
Conclusion: This study proves that PS is an effective and well-tolerated drug, showing results superior to glycerol, especially in patients with a longer pre-existing condition before therapy. The absence of a group treated with another established antibiotic is a limitation of this trial.