Preservatives and pH in low-dose atropine formulations for clinical trials

Over a century ago, atropine has been tested to arrest myopia progression with good results. In recent years, many randomized clinical trials have tested different concentrations against placebo. Three recent such studies with low-dose atropine showed that it was less effective than previous studies, even the last one showing no difference in myopia progression between the treated and control group. Previous randomized studies had been performed in Asian populations, and these last three were extended to Western Caucasian populations, based on the initial observation that differences in iris pigmentation could be a factor for a difference in effectiveness. We have noticed that the three last studies in the West have used the same patented formulation, while previous studies have preferred compounded low-dose atropine. Here we review how the power of hydrogen (pH) and preservatives could account for differences in drug penetration to the eye, possibly explaining the differences between studies.