Evaluation of investigator bias in industry-funded clinical trials of latanoprost

Objective: To determine whether sponsorship of prostaglandin analogue (PGA) clinical trials results in investigator bias in outcomes when studying intraocular pressure (IOP). Design: Retrospective, observational cohort study. Methods: A PubMed search was performed for latanoprost or Xalatan, bimatoprost or Lumigan, and travoprost or Travatan, with limits to humans, clinical trials, and English language. Inclusion criteria included randomized controlled trials, open-angle glaucoma, monotherapy with a PGA, baseline IOP >= 21 mm Hg, washout period, and minimum 1-month follow-up. Each article was reviewed by 2 independent reviewers. The results of IOP for each PGA were categorized as being sponsored by the parent company (the company manufacturing the PGA); by the competing company (the company manufacturing competing glaucoma therapy); or by a nonindustry source. The mean IOP and changes in IOP from baseline were compared among the 3 categories of sponsorship. Results: Only studies involving latanoprost were analyzed because of the low number of studies meeting the inclusion criteria for bimatoprost and travoprost. We found 29 and 13 studies that provided 1- and 3-month data, respectively, for analysis. The mean baseline IOPs in the 3 groups (parent company, competing company, nonindustry) were not significantly different (p = 0.47). The mean IOP at 1 (p = 0.72) and 3 months (p = 0.59) and the change in IOP from baseline (p = 0.83 and 0.90, respectively) were not significantly different in the 3 groups. A random-effects metaregression controlling for the covariates of blinding, naivete to PGAs, and baseline IOP < 24 mm Hg or >= 24 mm Hg did not change the findings. Conclusion: There was no evidence of investigator bias in determining outcomes for IOP in these clinical trials of latanoprost.