A Cochrane review included 9 studies with a total of 679 patients. One trial compared active treatments with no treatment, 3 compared active treatments with water or a saline 'placebo', and all 9 trials compared two or more active treatments. The majority of comparisons showed no difference between treatments. Meta-analysis of two high quality trials produced a statistical difference in favour of triethanolamine polypeptide over saline in preventing the need for syringing, but no other significant differences between treatments. In three trials, no difference was found between the effectiveness of either sodium bicarbonate ear drops, chlorbutanol, triethanolamine polypeptide oleate condensate or docusate sodium liquid versus a sterile water or saline 'placebo'. One trial found all 3 treatments - sodium bicarbonate ear drops, chlorbutanol and sterile water - to be significantly better than no treatment at preventing the need for syringing. None of the higher quality trials demonstrated superiority of one agent over another in direct comparisons.
Comment: The quality of evidence is downgraded by study quality (inadequate or unclear allocation concealment) and inconsistency (heterogeneity in treatments).