A Cochrane review included 9 trials involving a total of 616 participants. 6 trials compared an 'active' instillation with placebo instillation, two compared different types of instillation, and one was a comparison of an instillation plus bladder training versus bladder training alone. 6 different instillations were used. Resiniferatoxin was not associated with sustained differences in the review outcomes reported but pain during instillation and withdrawal from treatment were more common (2 trials, n=185). The data available about dimethyl sulfoxide (DMSO) were very limited but with no apparent differences from placebo (1 trial, n=33). Groups treated with BCG tended to report less pain and fewer general symptoms (2 trials, n=298). The few data about Pentosanpolysulphate tended to favour the actively treated (1 trial, n=20). Oxybutinin instillation was associated with increased bladder capacity, reduced frequency, improved quality of life scores and fewer drop-outs (1 trial, n=36). Alkalinisation of urine pH did not make any clear difference (1 trial, n=26).
Comment: The quality of evidence is downgraded by study quality (inadequate trial reports), by imprecise results (few patients and wide confidence intervals for each comparison), and by potential reporting bias.