Research
Influence of enrollment sequence effect on observed outcomes in the ADDRESS and PROWESS studies of drotrecogin alfa (activated) in patients with severe sepsis
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* Corresponding author: Pierre-François Laterre laterre@rean.ucl.ac.be
1 St Luc University Hospital, Avenue Hippocrate 10, 1200 Brussels, Belgium
2 Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, IN 46285, USA
3 Eli Lilly, Erl Wood Manor, Windlesham, Surrey GU20 6PH, UK
4 Department of Intensive Care, VU University Medical Center, De Boelelaan 1105, 1081 HVAmsterdam, The Netherlands
5 Paris Descartes University, rue de l'Ecole de Médecine, 75270 Paris Cedex 06, Paris, France
6 University of Alabama at Birmingham School of Medicine, 1530-3rd Avenue South, FOT 1203, Birmingham, AL 35294, USA
Critical Care 2008, 12:R117 doi:10.1186/cc7011
Published: 11 September 2008Abstract
Introduction
We performed a study to determine whether an enrollment sequence effect noted in the PROWESS (recombinant human activated Protein C Worldwide Evaluation in Severe Sepsis) trial exists in the ADDRESS (Administration of Drotrecogin Alfa [Activated] [DrotAA] in Early Stage Severe Sepsis) trial.
Methods
We evaluated prospectively defined subgroups from two large phase 3 clinical trials: ADDRESS, which included 516 sites in 34 countries, and PROWESS, which included 164 sites in 11 countries. ADDRESS consisted of patients with severe sepsis at low risk of death not indicated for treatment with DrotAA. PROWESS consisted of patients with severe sepsis with one or more organ dysfunctions. DrotAA (24 μg/kg per hour) or placebo was infused for 96 hours.
Results
In ADDRESS and PROWESS, there was a statistically significant interaction between the DrotAA treatment effect and the sequence in which patients were enrolled. In both trials, higher mortality was associated with DrotAA use in the subgroup of patients enrolled first at study sites. Compared with placebo, PROWESS mortality was lower with DrotAA treatment for the second and subsequent patients enrolled, whereas in ADDRESS, mortality remained higher for the second patient enrolled but thereafter was lower for DrotAA-treated patients. Comparison of patients enrolled first with subsequent patients enrolled indicated that the characteristics of patients changed. Subsequently enrolled patients were treated earlier, were less likely to suffer nonserious bleeds (ADDRESS), and experienced fewer protocol violations (PROWESS).
Conclusions
Analyses suggest that an enrollment sequence effect was present in the ADDRESS and PROWESS trials. Analysis of this effect on outcomes suggests that it is most apparent in patients at lower risk of death. In PROWESS, this effect appeared to be associated with a reduction of the DrotAA treatment effect for the first patients enrolled at each site. In ADDRESS, this effect may have contributed to early termination of the study. The finding of an enrollment sequence effect in two separate trials suggests that trial designs, site selection and training, data collection and monitoring, and statistical analysis plans may need to be adjusted for these potentially confounding events.
Trial Registration
ADDRESS trial registration number: NCT00568737. PROWESS was completed before trial registration was required.