Low power and striking results--a surprise but not a paradox

Conditional power for assessing population interventions

AIM

To calculate conditional power in comparative two-period studies with previously observed baseline data.

METHOD

Isolate the variability attributable to the yet-to-observed data and modify the standard power formulae.

RESULTS

For illustration, we examine rates of opioid overdose before and after a reformulation of one opioid product. The null hypothesis posited no impact of the reformulation, alternative hypotheses posited possible impacts, and ancillary hypotheses posited different secular pre-post changes directly observable in comparators. Conditional power varied with the size of the comparator population and with the assumed pre-post change for the comparator.

CONCLUSION

Pre-post designs can be initiated after the baseline period is over. Power calculations that are conditioned on observed baseline data account differently for variability in the baseline and follow-up periods.

PREventing Delayed Graft Function by Driving Immunosuppressive InduCtion Treatment (PREDICT-DGF): study protocol for a randomized controlled trial

Background

In kidney transplantation, the use of Anti-Thymocyte Globulins (ATG) as induction therapy has been described as a possible treatment for reducing the prevalence of Delayed Graft Function (DGF). ATG possesses pharmaceutical proprieties that could help control the lesions caused by ischemia reperfusion injury. However, other studies have questioned this potential protective effect. We hypothesized that the benefits related to ATG for reducing DGF prevalence may be higher and more consistently recognized if only patients with high DGF risk are considered. We recently proposed a scoring system entitled DGFS (Delayed Graft Function Score) for such stratification of kidney transplant recipients according to their risk of DGF. Using the DGFS calculation, we aim to determine whether a short course of ATG can decrease the incidence of DGF in comparison with Basiliximab in kidney transplant recipients with low immunological risk but high DGF risk.

Methods

We conduct a phase IV, open label, randomized, multicentric and prospective study, to compare ATG in parallel with a control group treated by Basiliximab. The 1:1 randomized allocation of patients between groups is stratified on the clinical center, and on the hypothermic machine-perfusion device. We aimed to include a total of 384 patients to achieve a statistical power at 0.80. The study was initiated at the Nantes University hospital in July 2014, with data collection continuing until April 2018, and publication of the results proposed for 2019.

Discussion

The main expected benefits of this study are i) the reduction of unjustified ATG over-prescriptions associated with serious adverse events, ii) the reduction of chance losses related to ATG under-prescription, iii) the decrease in the incidence of DGF which was described as a risk factor of graft failure and patient death, and iv) the reduction in hospitalization duration and number of post transplantation dialysis sessions, both being associated with reduced medical costs. In conclusion, the current study is innovative by proposing a more efficient and personalized induction therapy.

Trial registration

The study was registered in the Clinical Trials Registry (#NCT02056938, February 5, 2014), and in the European Clinical Trials Database (EudraCT #2014-000332-42, January 30, 2014).

Standardized parenteral alanyl-glutamine dipeptide supplementation is not beneficial in autologous transplant patients: a randomized, double-blind, placebo controlled study

We conducted a controlled, double-blind study of parenteral glutamine supplementation in an unselected group of consecutive autologous transplant patients. Patients received 30 g of alanyl-glutamine dipeptide (Dipeptiven; Fresenius-Kabi, Bad Homburg, Germany) or glutamine-free amino acid solution i.v. from day +1 to day +14 or to discharge. All patients were assessed for clinical status, mucositis, blood counts, oral intake and immune reconstitution. Parenteral nutrition was administered according to predefined guidelines. Forty patients were randomized; 21 into the glutamine and 19 into the placebo arm. Glutamine patients had less days with diarrhoea (3.3 +/- 4.0 vs 4.3 +/- 3.0, P = 0.03), but they had more severe oral mucositis (mean 4 +/- 4.7 vs 1.4 +/- 2.3 days of mucositis score >13, P = 0.04), spent more days on opioids (mean 3.5 +/- 4.2 vs 1.2 +/- 2.2 days, P = 0.03) and left hospital later than placebo patients (mean 13.5 +/- 3.1 vs 11.7 +/- 2.4 days after transplant, P = 0.06). There were more relapses (P = 0.02) and deaths (P = 0.05) in the glutamine group. The cost of supportive care (mean 2960 +/- 1694 vs 1534 +/- 513 Euro, P = 0.002) was also greater for glutamine patients, mainly due to the cost of glutamine dipeptide itself. The described mode and dosage of glutamine administration did not produce meaningful benefit in our autologous transplant patients and it was certainly not cost-effective.

Combined evidence from multiple outcomes in a clinical trial

Clinical investigators are encouraged to apply recently developed statistical methodology. For each patient in a trial, favorable and unfavorable results from multiple outcomes may be summarized in a suitable summary measure. This summary measure may be used in a two-sample t-test to decide which treatment is best. An example illustrates how the evidence from the main outcome criteria may be combined. The required study size depends on the mean treatment effect on the outcomes in the summary measure. When separate outcomes are considered, there is a multiple comparisons problem, for which Hochberg offered a simple solution. Evaluation of a single-summary measure may require a larger or a smaller study size than evaluation of separate outcomes, depending on whether treatment effects are about the same or very different.

Sample size formula with a continuous outcome for unequal group sizes and unequal variances

Guenther derived a simple formula for the accurate computation of equal sample sizes when the two-sample t-test with pooled variance estimate is used. In the present paper, the Guenther formula is generalized to the case of unequal sample sizes. In addition, the case of unequal variances is considered.

Preinfarction angina as a predictor of more rapid coronary thrombolysis in patients with acute myocardial infarction

BACKGROUND

When a myocardial infarction is preceded by angina, the infarct tends to be smaller than when there is no preinfarction angina. Prompt recanalization of the occluded infarct-related artery is crucial in limiting the size of the infarct. We prospectively studied the relation among preinfarction unstable angina, the speed of coronary reperfusion, and the size of the infarct in patients with acute myocardial infarction receiving thrombolytic therapy.

METHODS

We compared 14 patients who had unstable angina during the week before myocardial infarction with 9 patients who had no preinfarction angina. Coronary arteriograms were obtained at base line and 15, 35, 55, and 90 minutes and 24 hours after the start of thrombolytic therapy. The size of the infarct was estimated on the basis of creatine kinase and creatine kinase MB levels, which were measured every 4 hours during the first 24 hours.

RESULTS

Complete reperfusion (a flow of grade 3 according to the Thrombolysis in Myocardial Infarction classification) was achieved at 35 minutes in 64 percent of the patients with preinfarction angina but in none of those without preinfarction angina (P = 0.006); at 55 minutes in 86 percent and 38 percent, respectively (P = 0.05); and at 90 minutes in 86 percent and 50 percent, respectively (P = 0.14). The mean (+/- SD) time to reperfusion was 27 +/- 16 minutes in the group with preinfarction angina and 48 +/- 17 minutes in the group without preinfarction angina (P = 0.04); the peak creatine kinase levels were 1118 +/- 783 and 2395 +/- 1615 U per liter, respectively (P = 0.03); the peak creatine kinase MB levels were 102 +/- 67 and 251 +/- 186 U per liter, respectively (P = 0.009); and the 24-hour integrated creatine kinase MB levels were 1716 +/- 1171 and 4267 +/- 3252 U.liter-1 x 24 hours, respectively (P = 0.009). The time to reperfusion was positively correlated with the indexes of infarct size (r > or = 0.53, P < or = 0.02).

CONCLUSIONS

In patients with acute myocardial infarction preceded by unstable angina, as compared with those without preinfarction angina, thrombolytic therapy resulted in more rapid reperfusion and smaller infarcts. Earlier myocardial reperfusion may thus account for the smaller infarct size in patients with preinfarction angina.