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Using an External Control to Evaluate the Effectiveness of Posaconazole for Refractory Invasive Fungal Infections

Kenneth J. Koury

Jagadish P. Gogate

Schering-Plough Research Institute

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Refractory Invasive Fungal Infections(rIFI)

• Life-threatening infections• Limited therapeutic options, especially in

salvage setting• Randomized study

– straightforward interpretation of results– not practical to complete in a timely fashion– serious ethical issue: potential enrollment of

subjects into a failing regimen• No randomized trials completed for salvage

therapy for any antifungal drug

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Description of Study P00041

• Open-label, non-randomized, multinational, salvage therapy study

• Posaconazole oral suspension 400 mg bid• Subjects with invasive fungal infections

refractory to standard antifungal therapies or subjects who were intolerant of standard antifungal agents

• Started In January 1999 (compassionate use)• Enrollment expanded based on investigator

interest, completed by April 2001

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Advice from Regulatory Authorities

• CPMP (Committee for Proprietary Medicinal Products)– lack of randomized trial always makes it

difficult to evaluate a new agent– well-conducted external-control study may

provide a useful comparative reference– sponsor must demonstrate that any

potential selection bias was minimized– show that two groups are clinically similar

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Advice from Regulatory Authorities

• FDA– treatment for rIFI may fulfill an unmet medical

need – response rates from a control group required– numerous discussions regarding design and

analysis of external-control study (P02387)• comparability of patient populations• minimization of potential bias

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External-Control Study (P02387)

• Provide reference (benchmark) for comparison to P00041

• Procedures and methods prospectively implemented to minimize potential sources of bias

• Exhaustive review of all cases of IFI at study centers over target time period– 2073 screened for possible enrollment– 279 fulfilled criteria

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Control of Potential Bias

• External Data Review Committee (DRC)– 15 independent clinical experts and 2 radiologists– Concurrent, blinded review of data from 330

posaconazole-treated subjects (P00041) and 279 external-control subjects (P02387)

– Determined patient eligibility• met MSG/EORTC criteria for proven or probable IFI• met criteria for refractory disease or intolerance of

standard therapy or both

– Determined patient outcome: global response status at end of treatment

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Selection Bias

• Exhaustive review of all cases of IFI at study centers during comparable time period

• Similar inclusion and exclusion criteria• Autopsy data not used for identifying control

subjects• Exclude control subjects who died within 72

hours of after the initiation of therapy

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Information Bias

• Inherent differences in the amount of data available in a retrospective study vs. prospective study

• Develop uniform format for data presentation to maintain blinding of DRC

• Outcome data from a given subject are not available for review by DRC until eligibility of that subject has been determined

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Temporal and Geographic Bias

• Use same time frame (almost concurrent rather than historical controls)

• Use mostly same centers

• Expect controls to have similar disease characteristics to posaconazole-treated subjects

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Other Important Factors

• Primary pathogen (type of fungus)• Infection site• Underlying disease and associated

treatments – BMT, Solid Organ Transplant– Hematologic malignancies– HIV/Aids– Use of immune response modifiers, growth

factors

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Baseline and Disease Characteristics(With Potential to Influence Outcome)

• Demographic Variables: Age, Gender, Race and Weight.• Refractory Status• Intolerance Status• Period of Enrollment• Primary Pathogen: Aspergillus, Candida and Other

Yeast, Fusarium, Cryptococcus, Zygomycetes, Other Filamentous Fungi, Other Endemic Fungi and Multiple Pathogens

• Infection Site: pulmonary, extra pulmonary, disseminated with pulmonary involvement and disseminated without pulmonary involvement

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Baseline and Disease Characteristics (With Potential to Influence Outcome)

• Underlying Disease [9 variables each with two categories (present and absent]: Hematologic Malignancies, Non-Hematologic Malignancies, Nonmalignant Hematologic Disorders, Bone Marrow Transplant, Solid Organ Transplant, Renal Disease, Hepatic Disease, Immunocompromised- Acquired, Immunocompromised-Congenital

• Duration of prior effective antifungal therapy.• Baseline Neutropenia • Prior systemic corticosteroid use and Concurrent

systemic corticosteroid use

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Primary Efficacy Endpoint

DRC-adjudicated Global Response Status at the end of treatment– subject considered a “responder” if global

response at EOT was classified as a complete or partial response

– subject considered a “non-responder” if classified as stable disease, failure, or unable to determine

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Global Response Status• Complete Response

– Resolution of all attributable clinical signs and symptoms, radiological and mycological abnormalities, if present at baseline.

• Partial Response– Clinically meaningful improvement in attributable clinical signs and

symptoms, radiological and mycological abnormalities, if present at baseline.

• Stable Disease– No improvement in attributable clinical signs symptoms, radiological and

mycological abnormalities, if present at baseline

• Failure – Deterioration in attributable clinical signs and symptoms, radiological and/or

mycological abnormalities necessitating alternative antifungal therapy or resulting in death

• Unable to Determine– If for any reason the global response cannot be assessed (e.g., insufficient medical

records to determine outcome)

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Primary Analysis

• Modified ITT Population – subjects with proven or probable aspergillosis– refractory to standard therapy or intolerant

• Analysis of Global Response Rate– Logistic regression model includes:

• treatment• key prognostic factors• other potential prognostic factors (with treatment

imbalances at baseline)

– Assessment of treatment differences based on odds ratio for treatment effect and its 95% confidence interval

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Prognostic Variables

Key Variables• Refractory status• Intolerance status• Site of infection• Presence of baseline

neutropenia• Duration of prior

antifungal therapy• Region

Other Variables• All other baseline and

disease characteristics considered as potential prognostic variables

• Included as covariates in primary statistical analysis if treatment imbalance at baseline is significant (p<0.10)

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Supportive Analyses

Two step procedure• Preliminary analysis to identify prognostic indicators with

potential to influence global response– Based on a logistic regression procedure– All variables (except treatment) included– Variable selection option STEPWISE in PROC LOGISTIC of

SAS (significance level 0.15 for entry and 0.10 for stay)

• Statistical Modeling– Logistic regression on global response with treatment

and other covariates selected from the above procedure.

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Secondary Analyses

Survival Analyses• Time to Death (logrank test)

• Cox Proportional Hazards Model– Treatment Group– Site of Infection– Refractory Status, Intolerance Status– Baseline Neutropenia

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Additional Analyses

• Forming cohorts based on a Prognosis Score (low, intermediate, high risk)

• Use of Propensity scores

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Posaconazole (P00041)

Control (P02387)

Demography or Baseline Characteristic

N (%) N (%)

All Subjects Having Aspergillus as a Primary Pathogen 107 (100) 86 (100)

DEMOGRAPHY 18 to 64 years 90 (84) 74 (86) Male 71 (66) 62 (72) Caucasian 84 (79) 54 (63)a OTHER SUBJECT CHARACTERISTICS

Neutropenia (Baseline ANC < 500/mm3)

21 (20) 26 (30)

History of Bone Marrow Transplant 55 (51) 38 (44) Allogeneic 48 (45) 34 (40)

History of Solid Organ Transplant 12 (11) 7 (8) Hematologic Malignancy 79 (74) 70 (81) Renal Disease (baseline history of any renal disorder)

68 (64) 21 (24)

Hepatic Disease (baseline history of any hepatic disorder)

43 (40) 6 (7)

Baseline and Disease Characteristics

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Duration of Prior Effective Antifungal Therapy

30 days 69 (64) 71 (83)

31 to 60 days 21 (20) 8 (9) Enrollment Reason

Refractory 55 (51) 48 (56) Intolerant 13 (12) 18 (21) Refractory and Intolerant 39 (36) 20 (23)

General Site of Infection Pulmonary 79 (74) 67 (78)

a: Due to data privacy laws, the sponsor was not allowed to record race for 17 subjects enrolled in France. The races for these subjects were reported as Other (NA) and were handled as a subcategory of non Caucasian.

Baseline and Disease Characteristics

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Baseline Comparisons

• Both studies are comparable with respect to the distribution of demographic and almost all of the baseline disease characteristics

• Majority of the subjects are refractory to prior antifungal therapies

• Study P00041 has generally sicker patients (e.g., hepatic disease and renal disease)

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Global Response Rates (Complete+Partial)

Region P00041

(N=107)

P02387

(N=86)

US 38/94 (40.4%)

16/68 (23.5%)

Ex-US 7/13 (53.8%)

6/18 (33.3%)

All 45/107 (42.1%)

22/86 (25.6%)

•Unadjusted OR=2.11

•Confidence Interval for OR=(1.15, 3.92)

•p-value =0.018

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Primary Efficacy Analysis

• Logistic Regression on Global Response • Key Prognostic Factors included

– Refractory Status, Intolerance Status, Site of Infection, Neutropenia, Duration of Prior Antifungal Therapy, Age and Region of Enrollment.

• Potential Prognostic Factors with Baseline Imbalance– Enrollment Time, Race, Non-malignant Hematologic

Disorders, Renal Disease and Hepatic Disease

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Results of Primary Efficacy Analysis

• Only two significant variables in the model– Treatment and Baseline Neutropenia– No interaction between Treatment and

Neutropenia based on a logistic regression model with Treatment, Neutropenia and interaction between them

• Odds Ratio for Treatment: 4.06• P-value for the Treatment Effect: 0.006• 95% Confidence Interval: (1.50, 11.04)

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Impact on Odds Ratio for Treatment Effect Sequential Addition of Prognostic Variables

Variable Added in the Model Sequentially

Odds Ratio P-value

No covariate 2.11 0.0178

Neutropenia 1.94 0.040

Region 2.10 0.025

Hepatic Disease 2.55 0.010

Refractory Status 2.64 0.007

Intolerance Status 2.80 0.005

Infection Site 2.70 0.008

Non-malignant Hematologic Disorders

2.89 0.006

Age 2.88 0.007

Renal Disease 3.05 0.008

Prior AF duration 3.34 0.006

Enrollment Time 4.05 0.006

Race Group 4.06 0.006

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Supportive Analysis

• Variables associated with the Global Response selected using the Stepwise Logistic Regression– Baseline Neutropenia, Prior Corticosteroid Use, Solid

Organ Transplant

• Logistic regression on Global Response with Treatment and the above variables in the Model

• Odds Ratio for Treatment: 2.05

• P-value for the Treatment Effect: 0.034 Confidence Interval: (1.06, 3.97)

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Sensitivity AnalysesNo. Variations of the Prognostic Factors OR CI/P-value

1 Excluded Non-malignant Hematologic Disorders, Renal and Hepatic Disease

2.68 (1.15, 6.27)/ 0.023

2 Binary infection site, Continuous Age and Prior AF duration

3.67 (1.41, 9.54)/0.008

3 Binary Enrollment and Infection site, Continuous Age and Ordinal Prior AF duration

3.73 (1.51, 9.21)/0.004

4 Binary Enrollment and Infection Site, Continuous Age and Prior AF duration

3.45 (1.42, 8.41)/0.006

5 Ordinal Enrollment, Binary Infection site, Continuous Age and Ordinal Prior AF duration

3.48 (1.39, 8.72)/0.008

6 Ordinal Enrollment, Binary Infection site, Binary Prior AF duration (<=30, >30) and Continuous Age

3.69 (1.46, 9.35)/0.006

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Global Response Rates by Baseline Neutropenia

Study protocol

P00041 P02387

N % N %

Neutropenia Status:1/3 33.3

Missing

Neutropenia 5/21 23.8 2/26 7.7

No Neutropenia 35/78 44.9 19/58 32.8

Unable to Determine 4/5 80.0 1/2 50.0

Total 45/107 42.1 22/86 25.6

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Global Response Rates by Corticosteroid Use

Study protocol

P00041 P02387

N % N %

Prior Corticosteroid:

15/29 51.7 12/26 46.2No prior use

Prior use 30/78 38.5 10/60 16.7

Concomitant Corticosteroid:

13/23 56.5 7/27 25.9No Concomitant use

Concomitant use 32/84 38.1 15/59 25.4

Total 45/107 42.1 22/86 25.6

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Global Response Rates by Infection Site

Study protocol

P00041 P02387

N % N %

Infection Site

Pulmonary 31/79 39.2 17/67 25.4

Extra-Pulmonary 10/19 52.6 5/11 45.5

Disseminated with Pulmonary Involvement

1/3 33.3 0/3 0

Disseminated w/o Pulmonary Involvement

3/6 50 0/5 0

Total 45/107 42.1 22/86 25.6

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Global Response Rates by Underlying Disease Conditions

Study protocol

P00041(n=107)

P02387(n=86)

N % N %

Bone Marrow Transplant 21/55 38.2 7/38 18.4

Solid Organ Transplant 7/12 58.3 5/7 71.4

Hematologic Malignancies 29/79 36.7 16/70 22.9

Non-malignant Hematologic Disorders

36/91 39.6 11/52 21.2

Non-hematologic malignancies 6/13 46.2 1/5 20.0

Immunosuppressive-acquired 13/28 46.4 6/19 31.6

Immunosuppressive-congenital 1/2 50.0 0/3 0.0

Renal Disease 27/68 39.7 5/21 23.8

Hepatic Disease 16/43 37.2 0/6 0.0

No Identifiable Risk Factors 1/1 100.0

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Variables used for Prognosis Score

BMT, Solid Organ Transplant, Acquired Immunodeficiency, Congenital Immunodeficiency, Hematologic Malignancy, Non-hematologic Malignancy, Non-malignant Hematologic Disorder, Renal disease risk factor OR Creatinine >= Grade 1, Liver disease risk factor OR Total Bilirubin >= Grade 1 OR SGOT >= Grade 1 OR SGPT >= Grade 1, Prior Systemic Steroid use, Prior Immunosuppressive therapy, Prior Myelosuppressive therapy, Baseline Neutropenia, Baseline Mechanical Ventilation, and Baseline GVHD

Prognosis Score: one point added to subject’s score for each condition that is present

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Global Response Rate by Prognosis Score

Prognosis Score Group P00041Posaconazole

P02387Control

Low Risk (0-1) 2/2 (100%) -

Intermediate Risk (2-4) 10/21 (58%) 8/25 (32%)

High Risk (>=5) 33/48 (39%) 14/61 (23%)

All 45/107 (42%) 22/86 (26%)

P-value = 0.0202 based on CMH stratified analysis for general association.

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Propensity Scores

• Propensity Score is defined as the conditional probability of being treated given the covariates.

• Estimated propensity score can be used to reduce the bias through matching, stratification, regression adjustment or some combination of all three.

• Advantage of using propensity scores in estimating treatment effect is its simplicity in interpreting the results.

• Quantiles of the distribution of the propensity scores can be used as covariates in logistic regression analysis or as strata in assessing the treatment effect.

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Global Response Rate by Propensity Score Group

Propensity Score Group

P0041 P02387

<=0.177 0/1 (0%) 18/57(32%)

0.177- <=0.608

10/16 (63%) 3/18 (17%)

0.608- <=0.936

12/33 (36%) 1/9 (11%)

>0.936 23/57 (40%) 0/2 (0%)

All 45/107 (42%) 22/86 (26%)

P-value using the logistic regression is 0.0223

P value based on the CMH analysis is 0.0207

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Summary and Conclusions

• Posaconazole is substantially more effective than control for treatment of rIFI due to aspergillus

• The adjusted odds ratio obtained from the primary analysis is almost twice as large as the unadjusted odds ratio

• The treatment effect based on primary analysis is robust in the sense that it is not sensitive to the classification of baseline and disease characteristics used to specify the way in which the prognostic factors were incorporated in the analyses.

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Summary and Conclusions

The treatment effect is statistically significant even when the influential factors non-malignant hematologic disorders, hepatic disease and renal disease are excluded from the primary model (odds ratio=2.70, p-value=0.0227).

Alternate methods of controlling for prognostic factors confirm effectiveness of posaconazole.

Survival (based on the Kaplan-Meier estimates) is substantially longer in subjects treated with Posaconazole than control subjects. Kaplan-Meier estimates of the survival rates at the end of one year are 38 % and 22% in P0041 and P02387 respectively.