1. ¹BeSyRe Bekkering Systematic Reviews, Geel, Belgium
2. ²Department of General Practice, Catholic University of Leuven, Leuven, Belgium
3. ³Giza, Egypt
4. ⁴Kleijnen Systematic Reviews Ltd, York, UK

Correspondence: Dr GE Bekkering, Department of General Practice, Catholic University of Leuven, Kapucijnenvoer 33 Blok j—bus 7001, Leuven 3000, Belgium. E-mail: Trudy.Bekkering@med.kuleuven.be

Received 26 July 2007; Revised 10 November 2007; Accepted 10 November 2007; Published online 6 December 2007.

Abstract

A systematic review of PDE-5 inhibitors for erectile dysfunction was performed to evaluate the utility of quantitative methods for identifying and exploring the influence of bias and study quality on pooled outcomes from meta-analyses. We included 123 randomized controlled trials (RCTs). Methodological quality was poorly reported. All three drugs appeared highly effective. Indirect adjusted analyses showed no differences between the three drugs. Funnel plots and statistical tests showed no evidence of small-study effects for sildenafil whereas there was evidence of such bias for tadalafil and vardenafil. Adjustment for missing studies using trim and fill techniques did not alter the pooled estimates substantially. The exclusion of previous sildenafil nonresponders was associated with larger treatment effects for tadalafil. This investigation was hampered by poor reporting of methodological quality, a low number of studies, heterogeneity and large effect sizes. Despite such limitations, a comprehensive assessment of biases should be a routine in systematic reviews.