American Journal of Transplantation 2010; 10: 2571–2573Wiley Periodicals Inc.

C© 2010 The AuthorsJournal compilation C© 2010 The American Society of

Transplantation and the American Society of Transplant Surgeons

doi: 10.1111/j.1600-6143.2010.03323.xEditorial

The Noninferiority Trial: Don’t Don’t Do It

T. R. Srinivasa,*, B. Kaplanb

and H.-U. Meier-Krieschec

aDepartment of Nephrology and Hypertension, GlickmanUrological and Kidney Institute, Cleveland Clinic,Cleveland, OHbDepartment of Medicine – Renal Division, University ofArizona, Tucson, AZc Division of Nephrology, Hypertension andTransplantation, University of Florida, Gainesville, FL*Corresponding author: T. R. Srinivas, srinivt@ccf.org

Abbreviations: CNI, calcineurin inhibitor; BPAR,biopsy proven acute rejection; AUC, area under theconcentration-time curve.

Received 16 August 2010, revised 13 September 2010and accepted for publication 29 September 2010

In the early ’80s, in a popular song titled ‘White Lines’(Don’t Don’t Do It) Melvin Glover (Grandmaster Melle Mel)used the double negative to couch the song’s message onthe frenetic cocaine-fueled lifestyle in a socially acceptablerefrain (1). In present times, in medicine, the use of thedouble negative is inevitable in the reporting language ofthe noninferiority trial.

In the case of the song the double negative was usedintentionally. However in the case of noninferiority trialsuse of double negatives is a reflection of the complexi-ties of design and an inevitable confusion in terminologyensues. Thus a study showing that a drug is noninferiorneeds careful attention to avoid misinterpretation, as wediscuss below.

Noninferiority randomized controlled trials are increasinglyused to demonstrate that a new treatment for a conditionof interest is not inferior to standard therapy (active con-trol) (2,3). With decreasing acute rejection rates in recentyears, clinical trials in renal transplantation are increasinglybeing devised to show equal acute rejection prophylaxisbetween drugs or different formulations of a drug withsome other advantage (e.g. less toxicity) (2,3). As proof ofexact equality is impossible, a prestated margin of nonin-feriority (�) for the treatment effect in a primary outcomeis defined Figure 1 (2). This noninferiority margin is often-times somewhat arbitrary but usually based on prior data,clinical relevance or meta-analyses (2,3). A second primary

endpoint investigated with a superiority design is usuallyused to show an advantage of the new therapy and is usu-ally a requirement for regulatory purposes in the UnitedStates.

In this issue of the Journal, Kramer et al., report findingsfrom a multicenter randomized noninferiority study com-paring the efficacy and safety of twice daily tacrolimusand once daily prolonged release tacrolimus in de novo re-nal transplant recipients (4). The primary endpoint, biopsyproven acute rejection (BPAR) at 24 weeks by per protocolanalysis was reported as falling just outside the prespeci-fied noninferiority margin. The authors concluded that theonce daily formulation is an effective alternative to the es-tablished twice daily formulation.

In fact, the primary endpoint, BPAR by local read at 24weeks failed the primary study hypothesis.

The upper bound of the confidence interval of the pointestimate for the primary endpoint clearly crossed the pre-specified 10% noninferiority margin in fact with a non-significant p-value (Figure 1). The same held for all sec-ondary endpoints each of which failed the noninferiorityhypothesis (central 24-week, central all available biopsiesand local BPAR at 12 months (Figure 1). This study was welldesigned for this noninferiority setting. Given that acute re-jection is a dichotomous endpoint and the event rate wasas expected the confidence intervals was, not unexpect-edly, wide. In fact in looking at Figure 1 it becomes clearthat the crossing of the noninferiority margin was driven bythe higher point estimates of rejection and that if more pa-tients had been enrolled with a resulting narrowing of theconfidence interval the once a day formulation would prob-ably have been shown to be significantly inferior. Based onthis, a conclusion that the study drug is not noninferior tostandard therapy seems reasonably solid.

All point estimates for the primary endpoint and secondaryendpoints were numerically higher in the study group andstatistically insignificant. Unfortunately however, the inher-ent asymmetry of noninferiority designs renders them un-derpowered for a superiority adjudication of the same end-point (1,2).

Despite absence of a priori power to test for superior-ity, at 12 months the rejection rate assessed by cen-tral pathology was significantly higher in the once a daytacrolimus arm, 25.4% versus 17.5%; p = 0.026 (Figure 1).Rejections in the once a day tacrolimus arm were also

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Srinivas et al.

Figure 1: The solid lines punctuated by diamonds represent the point estimate, upper and lower bounds of the 95% confidence

interval of the difference between the treatment groups for the primary and secondary endpoints. The prestated noninferioritymargin (�; 10%) is depicted by the red vertical dashed line. All confidence intervals shown cross the noninferiority margin and do notallow inference of the noninferiority hypothesis. The upper bounds for all the confidence intervals exceed �. While the central BPAR ratedifference using all available biopsies was not the primary endpoint for adjudication of noninferiority, the p-value associated with the pointestimate for this parameter was significant with inferiority for this clinically relevant secondary endpoint.

numerically worse by treatment response and histologicalgrade even though some Banff Grade 3 rejections weredowngraded by central pathology reading (local pathologywas the defined endpoint).

Taken together, these findings suggest a relative lack ofefficacy of single dose tacrolimus in this study. This find-ing is interesting because trough tacrolimus levels weresimilar across study groups. As such, exposure would beexpected to be similar assuming that the trough to areaunder the concentration-time curve (AUC) ratio for bothdrug formulations is identical. If the trough to AUC ratio isindeed identical for both drugs, efficacy failure would thenneed to be explained based on differing peak levels. Whilenot specifically reported in this study, peak levels are in-herently lower with the once a day formulation comparedto the twice a day formulation (4). Although, it has neverbeen definitively determined whether calcineurin inhibitor(CNI) efficacy in general and tacrolimus efficacy in particu-lar is best correlated with AUC, peak or trough, if the AUCswere similar in this study the obvious conclusion would bethat the observed efficacy failure is most likely related tolower and less frequent peaks with the once a day formu-lation. Interestingly, in the other phase III trial with once a

day tacrolimus, rejection rates were also higher comparedto twice a day tacrolimus with equivalent trough levelsthroughout the study, a further indication that the lowerand less frequent tacrolimus peak might be detrimental toefficacy (5).

In addition, in this study at all time points, tacrolimus dosesneeded to achieve a given trough were higher with oncedaily tacrolimus and trough levels were lower with oncedaily tacrolimus in the immediate 7 days posttransplantconsistent with prior studies (5,6). This is however, differ-ent from what has been described in stable patients wherea 1:1 conversion has been described (7).

Another possible explanation for the excess rejectionson once daily tacrolimus which was not directly testedin this study is a potential differential effect of the twotacrolimus formulations on the enterohepatic recirculationof mycophenolic acid glucuronide and consequent overallmycophenolic acid exposure (8).

A potential confounding variable could be steroid with-drawal, if indeed it was more frequently used in the oncea day tacrolimus arm.

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The Noninferiority Trial: Don’t Don’t Do It

A stated aim underlying the development of the once dailytacrolimus formulation is improved treatment adherence(4,5). Unfortunately however, no direct measures of adher-ence were built into this study.

In the larger picture, this study exposes the Achilles heelof noninferiority trials: (i) the arbitrary nature of the non-inferiority margin and (ii) the complexities inherent toreporting statistical significance in this field of inquiry(2,3). As such the reader must pay close attention to clin-ically important findings pertinent to efficacy and safetyand also carefully scrutinize secondary endpoints and thereporting of statistical significance.

Given these complexities we feel the published data fromthis study can be interpreted as a lack of efficacy and advicecaution in the use of the once-daily tacrolimus formulation.On the other hand, the study offers some fascinating newinsights into the potential effect of pharmacokinetics ofdifferent tacrolimus formulations on outcomes.

Disclosure

The authors of this manuscript have no conflicts of inter-est to disclose as described by the American Journal ofTransplantation.

References

1. Melle Mel G. White Lines (Don’t Don’t Do It). Glover M (Grandmas-ter/Melle Mel). New York Sugar Hill Records, 1983.

2. Parienti JJ, Verdon R, Massari V. Methodological standards in non-inferiority AIDS trials: moving from adherence to compliance. BMCMed Res Methodol 2006; 6: 46–55.

3. Piaggio G, Elbourne DR, Altman DG, Pocock SJ, Evans SJ. Reportingof noninferiority and equivalence randomized trials: an extension ofthe CONSORT statement. JAMA 2006; 295: 1152–1160.

4. Kramer BK, Charpentier B, Backmann L et al. Tacrolimus once daily(ADVAGRAF) versus twice daily (PROGRAF) in de novo renal trans-plantation: A randomized phase III study. Am J Transplant 2010; 10:2632–2643.

5. Silva HT Jr, Yang HC, Abouljoud M et al. One-year resultswith extended-release tacrolimus/MMF, tacrolimus/MMF and cy-closporine/MMF in de novo kidney transplant recipients. Am JTransplant 2007; 7: 595–608.

6. Crespo M, Mir M, Marin M et al. De novo kidney transplantrecipients need higher doses of Advagraf compared with Pro-graf to get therapeutic levels. Transplant Proc 2009; 41: 2115–2117.

7. Alloway R, Steinberg S, Khalil K et al. Conversion of stable kidneytransplant recipients from a twice daily Prograf-based regimen to aonce daily modified release tacrolimus-based regimen. TransplantProc 2005; 37: 867–870.

8. Hesselink DA, van Hest RM, Mathot RA et al. Cyclosporine inter-acts with mycophenolic acid by inhibiting the multidrug resistance-associated protein 2. Am J Transplant 2005; 5: 987–994.

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