tessella webinar 6 18-2013 v3

A Novel Phase 3 Design Incorporating

Historical Information for the Development of

Antibacterial Agents

Jeff Wetherington, GSK

Kert Viele, Berry Consultants

Tessella Series Webinar

June 18th, 2013

Complicated Urinary Tract

Infections (1)

• Occurs in men and women

– structural or functional abnormalities of the urinary

tract

– hospitalized patients with significant medical or

surgical co-morbidities

• Major cause of hospital admission, extended hospitalizations morbidity, mortality, and excess healthcare costs

• Prescribing physicians have several options for empiric and pathogen-specific treatment

Bayesian Augmented Control for Antibacterial Agents 2

Complicated Urinary Tract

Infections (2)

Yet unmet treatment needs for patients with cUTI

continue to exist given the emergence and

prevalence of multi-drug resistance in uropathogens


Traditional Phase 3

• Randomized, parallel group

• Active controlled, non inferiority

• Narrow non inferiority margins

• Infeasible in the face of increasing unmet need

– >1500 patients enrolled into 2 independent trials

– >5 year clinical development programs

• Urgent need for novel clinical designs for

antibiotic drug development


Historical Studies


0.0

0.2

0.4

0.6

0.8

1.0

Naber 2009 Redman 2010

Doripenem Microbiological Eradication Rate

Fixed Design

• “Standard” 1:1 trial requires 750 subjects total

– 90% power and one sided α=0.025

– power for p=0.83 with noninferiority δ=0.10

– 20% dropout assumed

– note 375 patients on treatment

• Can we do better using the historical

information?


Goals

• Reduce sample size!

• Reduce sample size!

• Maintain

– controlled type I error (most complex…won’t be

able to get “complete” control)

– comparable power around (and slightly below per

expectation) p=0.83

– similar numbers of subjects on treatment (for

secondary analyses)


Preview

• Proposed design incorporates historical borrowing on the control arm using a hierarchical model.

• 20% reduction in sample size

• Similar power near or slight below p=0.83

• Slightly MORE subjects on treatment

• Type I error control

– in a region near 0.83

– based on E[type I error] for a range of perceived likely amounts of “drift” in the true control rate


Experimental parameters

• Dichotomous endpoint, p=Pr(ME)

• Control = Doripenum versus Treatment

• 20% dropout rate

• Goal is 90% for p=0.83 (NI δ=0.10) with

one sided α=0.025

• If possible, would like to leverage two

historical studies from control arm.

– Naber, 230 successes in 280 subjects (82.1%)

– Peninsula, 209 successes in 250 subjects (83.6%)


Notation and Model

• γ0 = logit(true current control rate)

• γ1 = logit(true Naber rate)

• γ2 = logit(true Peninsula rate)

• γ0,γ1,γ2 ~ N(μ,τ)

• π(μ)=N(1,1)

• π(τ2)=IGamma(α=0.001,β=0.001)

• Treatment effect θ ~ N(μθ=0,σθ=100)

• γ0+θ = logit(true treatment rate)


Intuition

• The three Doripenem arms are connected

through the “across studies” distribution

N(µ,τ).

– similar to random effects model on studies

– common model in meta-analysis

• τ is the most important parameter (across

study variance)

– τ≈0 corresponds to γ0≈γ1≈γ2

– τ large corresponds to no borrowing


Intuition • τ has a prior, and is estimated as part of the

model fitting.

• Datasets with high across study variation – produce higher estimates of τ

– the N(µ,τ) across distribution exerts less influence on each group (acts as less informative prior)

– less borrowing

• Datasets with low across study variation – produce lower estimates of τ

– the N(µ,τ) across study distribution can act as quite informative prior

– more borrowing


Intuition

• Only 3 Doripenem arms available

– so only three γ used to estimate τ

• Enough that borrowing is dynamic, but prior

will not fully wash out.

• Important to consider operating

characteristics (as always)

• Big goal

– borrow robustly when current data near p=0.83

– borrow less as current data diverges from p=0.83


Proposed Design A

• N=600 with 2:1 randomization and

borrowing

– 20% savings on N compared to fixed design

– 400 subjects on treatment, more than fixed

design

• Trial declared success if

– Pr(trt rate > ctrl rate – 10%)>0.975



Data


horizontal dashed

line is historical rate


control arm CIs

under none,full

and hierarchical

borrowing


Treatment CI

(same for all borrowing

as prior is noninformative)


Effective

borrowing

N=mean(p)*(1-mean(p)) / var(p)

numborrowed=N-233


probability of trial

success under each

kind of borrowing

Dynamic borrowing

• The effective amount of borrowing for

193/233 on control (almost identical to

history) is 225 of the 530 historical subjects

• Hierarchical modeling produces dynamic

borrowing.

– as the current control varies away from 82.9%

(history), the amount of borrowing decreases



Observed control proportion (x) versus

effective number of borrowed observations (y)

Summary

• The hierarchical model produces dynamic borrowing (through estimation of τ)

– Many historical subjects are borrowed when the current data is consistent with history

– Few historical subjects are borrowing when the current data is inconsistent

• Most effective (gains the most information) if the historical data is “on point”.

• If you happen to get inconsistent data, less borrowing occurs mitigating the costs.


Operating Characteristics

• For all designs, evaluated Pr(trial success) for

– control rates 0.780, 0.805, 0.830, 0.855, 0.880

– treatment rates 10% lower, 5% lower, equal, or

5% greater than control

• Treatment rates 10% lower were used to

compute type I error

• Equal treatment rates used to compute

power.



Trt -10% Trt -5% Trt equal Trt +5%

Control 0.780 0.024 / 0.006 0.309 / 0.119 0.842 / 0.702 0.996 / 0.990

Control 0.805 0.026 / 0.007 0.321 / 0.229 0.874 / 0.861 0.996 / 0.997

Control 0.830 0.026 / 0.017 0.342 / 0.376 0.910 / 0.942 0.998 / 0.999

Control 0.855 0.028 / 0.045 0.372 / 0.564 0.929 / 0.966 1.000 / 1.000

Control 0.880 0.030 / 0.100 0.421 / 0.642 0.954 / 0.976 1.000 / 1.000


Table shows Pr(trial success)

Two entries per cell in the form FIXED / DESIGN A

Design aims to produce greater power AND lower type

I error for consistent control data, with 20% savings on N.

Here type I error reduced from 0.026 to 0.017 AND

power increased from 91% to 94.2%.

Type I error Power



Control 0.780 0.024 / 0.006 0.309 / 0.119 0.842 / 0.702 0.996 / 0.990

Control 0.805 0.026 / 0.007 0.321 / 0.229 0.874 / 0.861 0.996 / 0.997

Control 0.830 0.026 / 0.017 0.342 / 0.376 0.910 / 0.942 0.998 / 0.999

Control 0.855 0.028 / 0.045 0.372 / 0.564 0.929 / 0.966 1.000 / 1.000

Control 0.880 0.030 / 0.100 0.421 / 0.642 0.954 / 0.976 1.000 / 1.000




With slight reduction in true control rate, design still

obtains nearly equivalent power.

Type I error Power



Control 0.780 0.024 / 0.006 0.309 / 0.119 0.842 / 0.702 0.996 / 0.990

Control 0.805 0.026 / 0.007 0.321 / 0.229 0.874 / 0.861 0.996 / 0.997

Control 0.830 0.026 / 0.017 0.342 / 0.376 0.910 / 0.942 0.998 / 0.999

Control 0.855 0.028 / 0.045 0.372 / 0.564 0.929 / 0.966 1.000 / 1.000

Control 0.880 0.030 / 0.100 0.421 / 0.642 0.954 / 0.976 1.000 / 1.000




If true current control rate is higher than observed

historical rate, power is increased, but we also observe

inflated type I error.

Type I error Power



Control 0.780 0.024 / 0.006 0.309 / 0.119 0.842 / 0.702 0.996 / 0.990

Control 0.805 0.026 / 0.007 0.321 / 0.229 0.874 / 0.861 0.996 / 0.997

Control 0.830 0.026 / 0.017 0.342 / 0.376 0.910 / 0.942 0.998 / 0.999

Control 0.855 0.028 / 0.045 0.372 / 0.564 0.929 / 0.966 1.000 / 1.000

Control 0.880 0.030 / 0.100 0.421 / 0.642 0.954 / 0.976 1.000 / 1.000




If true current control rate is much lower than the observed

historical rate, then power is reduced (type I error rate

is negligible).

Type I error Power

Summary for Design A • Pros

– 20% reduction in sample size

– more patients on treatment

– increased or equivalent power for true control rates near observed historical data.

– essentially, there is a “sweet spot” where Design A dominates the fixed trial.

• Cons – inflated type I error for true control rates much

above observed historical control rates.

– decreased power for true control rates much below observed historical data


Design B

• As with design A, hierarchical borrowing and

2:1 randomization, with maximum N=600.

• Incorporates futility stopping

– interim analyses N=300, 400, 500, 600.

– trial stopped for futility if

Pr(non-inferiority)<0.15

• Evaluated operating characteristics as before,

including expected sample size.




Control 0.780 0.006 / 0.005

456.0

0.119 / 0.133

572.5

0.702 / 0.692

598.5

0.990 / 0.994

599.7

Control 0.805 0.007 / 0.010

499.7

0.229 / 0.237

589.9

0.861 / 0.851

599.7

0.997 / 0.998

599.7

Control 0.830 0.017 / 0.019

537.9

0.376 / 0.376

595.7

0.942 / 0.938

599.7

0.999 / 0.999

599.7

Control 0.855 0.045 / 0.048

569.3

0.564 / 0.567

598.2

0.966 / 0.968

599.7

1.000 / 0.999

599.7

Control 0.880 0.100 / 0.096

580.2

0.642 / 0.638

598.3

0.976 / 0.970

599.7

1.000 / 0.999

599.7


Three entries per cell. Top two are Pr(trial success)

in the form DESIGN A / DESIGN B. Lower number

is expected N (max 600)

Can save another

60-140 subjects

under null hypothesis

depending on true

control rate.



Control 0.780 0.006 / 0.005

456.0

0.119 / 0.133

572.5

0.702 / 0.692

598.5

0.990 / 0.994

599.7

Control 0.805 0.007 / 0.010

499.7

0.229 / 0.237

589.9

0.861 / 0.851

599.7

0.997 / 0.998

599.7

Control 0.830 0.017 / 0.019

537.9

0.376 / 0.376

595.7

0.942 / 0.938

599.7

0.999 / 0.999

599.7

Control 0.855 0.045 / 0.048

569.3

0.564 / 0.567

598.2

0.966 / 0.968

599.7

1.000 / 0.999

599.7

Control 0.880 0.100 / 0.096

580.2

0.642 / 0.638

598.3

0.976 / 0.970

599.7

1.000 / 0.999

599.7


Three entries per cell. Top two are Pr(trial success)

in the form DESIGN A / DESIGN B. Lower number

is expected N (max 600)

Very slight

changes to

power

Summary for Design B

• Similar Pros/Cons relative to fixed design

• Pros relative to design A

– can save 60-140 subjects on average when null hypothesis is true

– when drug is noninferior, design very rarely stops for futility.

– successful trials retain 400 subjects on treatment.

• Cons relative to design A

– very slight power loss (simulations all have 1% or less power loss)


Statistical Summary

• Hierarchical Modeling allows for competitive

alternatives to fixed designs with significant

sample size savings

• Possible risks are associated with drift in the

true control rate from observed historical

rate.

• Futility stopping can result in additional

sample size savings under null hypothesis

without significant cost to power.


Conclusions

• Hierarchical Modeling allows for

competitive alternatives to fixed designs with

significant reduction in cycle time

• Possible risks are associated with drift in the

true control rate from observed historical rate

• Futility stopping can result in minimizing

exposure to ineffective therapy under null

hypothesis without significant cost to power


tessella webinar 6 18-2013 v3

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