Early Termination of Clinical Trials—2012 Update
Several years ago we presented the increasing evidence of problems with early termination of clinical trials for benefit after interim analyses. The bottom line is that results are very likely to be distorted because of chance findings. A useful review of this topic has been recently published. Briefly, this review points out that—
- Frequently trials stopped early for benefit report results that are not credible, e.g., in one review, relative risk reductions were over 47% in half, over 70% in a quarter. The apparent overestimates were larger in smaller trials.
- Stopping trials early for apparent benefit is highly likely to systematically overestimate treatment effects.
- Large overestimates were common when the total number of events was less than 200.
- Smaller but important overestimates are likely with 200 to 500 events, and trials with over 500 events are likely to show small overestimates.
- Stopping rules do not appear to ensure protection against distortion of results.
- Despite the fact that stopped trials may report chance findings that overestimate true effect sizes—especially when based on a small number of events—positive results receive significant attention and can bias clinical practice, clinical guidelines and subsequent systematic reviews.
- Trials stopped early reduce opportunities to find potential harms.
The authors provide 3 examples to illustrate the above points where harm is likely to have occurred to patients.
Case 1 is the use of preoperative beta blockers in non-cardiac surgery in 1999 a clinical trial of bisoprolol in patients with vascular disease having non-cardiac surgery with a planned sample size of 266 stopped early after enrolling 112 patients—with 20 events. Two of 59 patients in the bisoprolol group and 18 of 53 in the control group had experienced a composite endpoint event (cardiac death or myocardial infarction). The authors reported a 91% reduction in relative risk for this endpoint, 95% confidence interval (63% to 98%). In 2002, a ACC/AHA clinical practice guideline recommended perioperative use of beta blockers for this population. In 2008, a systematic review and meta-analysis, including over 12,000 patients having non-cardiac surgery, reported a 35% reduction in the odds of non-fatal myocardial infarction, 95% CI (21% to 46%), a twofold increase in non-fatal strokes, odds ratio 2.1, 95% CI (2.7 to 3.68), and a possible increase in all-cause mortality, odds ratio 1.20, 95% CI (0.95 to 1.51). Despite the results of this good quality systematic review, subsequent guidelines published in 2009 and 2012 continue to recommend beta blockers.
Case 2 is the use of Intensive insulin therapy (IIT) in critically ill patients. In 2001, a single center randomized trial of IIT in critically ill patients with raised serum glucose reported a 42% relative risk reduction in mortality, 95% CI (22% to 62%). The authors used a liberal stopping threshold (P=0.01) and took frequent looks at the data, strategies they said were “designed to allow early termination of the study.” Results were rapidly incorporated into guidelines, e.g., American College Endocrinology practice guidelines, with recommendations for an upper limit of glucose of </=8.3 mmol/L. A systematic review published in 2008 summarized the results of subsequent studies which did not confirm lower mortality with IIT and documented an increased risk of hypoglycemia. Later, a good quality SR confirmed these later findings. Nevertheless, some guideline groups continue to advocate limits of </=8.3 mmol/L. Other guidelines utilizing the results of more recent studies, recommend a range of 7.8-10 mmol/L.15.
Case 3 is the use of activated protein C in critically ill patients with sepsis. The original 2001 trial of recombinant human activated protein C (rhAPC) was stopped early after the second interim analysis because of an apparent difference in mortality. In 2004, the Surviving Sepsis Campaign, a global initiative to improve management, recommended use of the drug as part of a “bundle” of interventions in sepsis. A subsequent trial, published in 2005, reinforced previous concerns from studies reporting increased risk of bleeding with rhAPC and raised questions about the apparent mortality reduction in the original study. As of 2007, trials had failed to replicate the favorable results reported in the pivotal Recombinant Human Activated Protein C Worldwide Evaluation in Severe Sepsis (PROWESS) study. Nevertheless, the 2008 iteration of the Surviving Sepsis guidelines and another guideline in 2009 continued to recommend rhAPC. Finally, after further discouraging trial results, Eli Lilly withdrew the drug, activated drotrecogin alfa (Xigris) from the market 2011.
Key points about trials terminated early for benefit:
- Truncated trials are likely to overestimate benefits.
- Results should be confirmed in other studies.
- Maintain a high level of scepticism regarding the findings of trials stopped early for benefit, particularly when those trials are relatively small and replication is limited or absent.
- Stopping rules do not protect against overestimation of benefits.
- Stringent criteria for stopping for benefit would include not stopping before approximately 500 events have accumulated.
2. Guyatt GH, Briel M, Glasziou P, Bassler D, Montori VM. Problems of stopping trials early. BMJ. 2012 Jun 15;344:e3863. doi: 10.1136/bmj.e3863. PMID:22705814.