Convincing the Pharmaceutical Industry to Use Surrogates for Antibiotic Development:
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Convincing the Pharmaceutical Industry to Use Surrogates for Antibiotic Development: What is Gained and What is Lost. G.L. Drusano, M.D. Co-Director Ordway Research Institute Professor and Director Division of Clinical Pharmacology Albany Medical College Research Physician

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G l drusano m d co director ordway research institute professor and director

Convincing the Pharmaceutical Industry to Use Surrogates for Antibiotic Development: What is Gained and What is Lost

G.L. Drusano, M.D.

Co-Director

Ordway Research Institute

Professor and Director

Division of Clinical Pharmacology

Albany Medical College

Research Physician

Wadsworth Center, David Axelrod Institute

New York State Department of Health


Surrogates antibiotic development

Surrogates & Antibiotic Development

  • First, let me state my understanding of “surrogates”

  • It is important to acknowledge the very nice slide deck of Dr. Arthur Atkinson posted on the WEB

  • For antibiotic trials, we can have a surrogate endpoint as well as a biomarker (or surrogate marker, if you do not mind bucking the following guys, who will be happy to meet you out back)

    BIOMARKERS DEFINITIONS WORKING GROUP: BIOMARKERS AND SURROGATE ENDPOINTS: PREFERRED DEFINITIONS AND CONCEPTUAL FRAMEWORK. CLIN PHARMACOL THER 2001;69:89-95.

    The surrogate endpoint can be microbiological outcome instead of clinical outcome. The biomarker can be a transformation of the measured drug concentration (e.g. free drug AUC/MIC ratio or free drug Time > MIC)

    All of the above is definition driven by statisticians


Surrogates antibiotic development1

Surrogates & Antibiotic Development

  • So, for antibiotic studies, we can measure a biomarker and we can use a surrogate endpoint

  • While measuring the biomarker is straightforward, there are issues about the surrogate endpoint (discussed shortly)

  • Why do we do reasonably well with identifying exposure-response relationships in anti-infective trials?

  • The answer is that the MIC gives us a normalizing measure for docking the same drug into different receptors (different bacteria)


Surrogates antibiotic development2

Surrogates & Antibiotic Development

  • For antibiotics, we try to develop relationships between some measure of drug exposure and some measure of effect

  • Most often, these are clinical or microbiological outcome, both of which are dichotomous outcome variables


Surrogates antibiotic development3

Surrogates & Antibiotic Development

  • We have seen Dr. Forrest present a large number of patient studies, BUT were one to perform a literature search, I would expect that the numbers of such studies would differ from the numbers of in vitro and animal studies by several orders of magnitude

  • Why the difference?

  • First, the former measure colony counts (a continuous variable) while the latter deal with dichotomous outcome variables


Surrogates antibiotic development4

Surrogates & Antibiotic Development

  • Second, it is MUCH cheaper and faster to perform in vitro and animal studies

  • So, what can we gain from the former and what from the latter?

  • It is important to remember that the FDA, IDSA and ISAP recently held a workshop that addressed much of this

  • Most of the outcome can be addressed with one slide, after which I will guild the lilly


Closing the loop

This is what the FDA expects from sponsors

“Closing the Loop”

In-Vitro/ Animal Models

Phase 3 Studies

Phase 2 Studies

Phase 1 Studies

Pre-Clinical

Clinical Development

Office of Clinical Pharmacology and Biopharmaceutics IDSA/ISAP/FDA Workshop 4/16/04 – Dr. Charles Bonapace


Surrogates antibiotic development5

Surrogates & Antibiotic Development

  • Let us first examine preclinical studies

  • At the point of entry into Phase I trials, we are trying to choose a safe and effective dose for Phase II and Phase III trials

  • So, what do we need?♦ An exposure target (hence the preclinical studies♦ Population pharmacokinetic information♦ Protein binding data from animals & man♦ Target organism MIC distribution


G l drusano m d co director ordway research institute professor and director

Drusano GL. Nat Rev Microbiol 2004;2:289-300

Journal of Clinical Investigation 2003;112:275-285 &

Nature Reviews Microbiology 2004;2:289-300


G l drusano m d co director ordway research institute professor and director

90 mg/kg

0 mg/kg

215 mg/kg

600 mg/kg

Journal of Clinical Investigation 2003;112:275-285 &

Nature Reviews Microbiology 2004;2:289-300

Jumbe et al J Clin Invest 2003;112:275-285


G l drusano m d co director ordway research institute professor and director

Peripheral (thigh)

Compartment (Cp)

Bacteria

(XT/R)

+

kpc

f(c)

kcp

Central Blood

Compartment (Cc)

dXS=KGS xXS x L - fKS(CcH) x XS

dt

[4]

IP

injection

[5]

dXR= KGR xXR x L- fKR(CcH) x XR

dt

[6]

L = (1- (XR + XS)/POPMAX)

ke

KmaxCcH

C H 50+CcH 

dCa= -kaCa

dt

, =K and = S,R

[1]

[7]

f(CcH)=

dCc= kaCa+kpcCp-kcpCc-keCc

dt

[2]

Y1=XT=XS+XR

Y2=XR

[8]

dCp = kcpCc - kpc Cp

dt

[3]

[9]


Mean parameter estimates of the model

Mean Parameter Estimates of the Model.

KmaxGS

0.117

KmaxGR

0.163

C50KS

123.5

C50KR

129.8

HKS

6.26

HKR

2.37

KmaxKS

94.01

KmaxKR

12.16

Popmax = 3.6 x 1010

KmaxG -maximum growth rate (hr-1) in the presence of drug

KmaxK -maximum kill rate (hr-1)

C50K -drug concentration (g/mL) to decrease kill rate by half

HK -rate of concentration dependent kill

Popmax -maximal population size


G l drusano m d co director ordway research institute professor and director

Jumbe et al J Clin Invest 2003;112:275-285

Drusano GL. Nat Rev Microbiol 2004;2:289-300


Surrogates antibiotic development6

Surrogates & Antibiotic Development

Jumbe et al J Clin Invest 2003;112:275-285

Drusano GL. Nat Rev Microbiol 2004;2:289-300


G l drusano m d co director ordway research institute professor and director

Jumbe et al J Clin Invest 2003;112:275-285

Drusano GL. Nat Rev Microbiol 2004;2:289-300

Journal of Clinical Investigation 2003;112:275-285 &

Nature Reviews Microbiology 2004;2:289-300


Surrogates antibiotic development7

Surrogates & Antibiotic Development

Pre-Clinical to Phase I/II: What about Resistance?

Can this be done in vitro?


Surrogates antibiotic development8

Surrogates & Antibiotic Development

The hollow fiber model was described by Blaser and Zinner and employed

extensively by Dudley


Surrogates antibiotic development9

Surrogates & Antibiotic Development

Tam V et al. Bacterial-population responses to drug selective pressure: Examination of

garenoxacin’s effect on Pseudomonas aeruginosa. J Infect Dis 2005;192:420-428


G l drusano m d co director ordway research institute professor and director

Surrogates & Antibiotic DevelopmentP. aeruginosa - Prevention of Amplification of Resistant Subpopulation

  • The amplification of the resistant sub-population is a function of the AUC/MIC ratio

  • The response curve is an inverted “U”.

  • The AUC/MIC ratio for resistant organism stasis is circa 185/1

Resistant organisms

at baseline

All other data points represent

resistant organism counts at

48 hours of therapy


Surrogates antibiotic development10

Surrogates & Antibiotic Development

Propspective Validation Study

Tam V et al. Bacterial-population responses to drug selective pressure: Examination of

garenoxacin’s effect on Pseudomonas aeruginosa. J Infect Dis 2005;192:420-428


Surrogates antibiotic development11

Surrogates & Antibiotic Development

  • We can bridge preclinically to Phase II/III through the use of Monte Carlo simulation

  • This is the plot of probability for target attainment (resistance-suppression exposure) for a FQ as derived from the preclinical model

Jumbe et al J Clin Invest 2003;112:275-285


Surrogates antibiotic development12

Surrogates & Antibiotic Development

  • The previous data was for resistance, but straightforward cell kill is also possible

  • Later we will see how much kill correlates with what happens in clinical trials

  • BUT, please remember that a total drug AUC/MIC = 88 gives a 2 log kill

Jumbe et al J Clin Invest 2003;112:275-285


Surrogates antibiotic development13

Surrogates & Antibiotic Development

  • We can also perform such studies in Phase II/III, as Dr. Forrest has already shown you

  • As an example, a trial of nosocomial pneumonia with the same FQ as in the mouse study will be presented


G l drusano m d co director ordway research institute professor and director

Population mean pharmacokinetic parameter values derived from 58 Patients

with Nosocomial Pneumonia Receiving Levofloxacin as a 1.5 Hour Constant

Rate, Intravenous Infusion Vol Kcp Kpc CL

Units L hr-1 hr-1 L/hr

Means 34.4 7.65 6.07 7.24

Medians 23.3 2.66 0.924 6.24

S.D. 33.5 9.59 12.0 4.36

Vol = Volume of the central compartment; Kcp and Kpc are first order ntercompartmental

transfer rate constants connecting the central and peripheral compartments; CL = Total clearance of Levofloxacin

Drusano GL, SL Preston, C Fowler, M Corrado, B Weisinger, J Kahn

J Infect Dis. 2004;189:1590-1597.


G l drusano m d co director ordway research institute professor and director

Final model for microbiological outcome for patients with

nosocomial pneumonia receiving levofloxacin daily

Final Model for Microbiological Outcome

ConstantParameterOdds Ratio95% Confidence Interval for Odds Ratio

(AUC/MIC > 87)

-2.197

1.3743.95211.596 – 1.347

(Age)

0.0671.0691.138 - 1.004

p = 0.001; McFadden’s 2 = 0.31

Drusano GL, SL Preston, C Fowler, M Corrado, B Weisinger, J Kahn

J Infect Dis. 2004;189:1590-1597.


G l drusano m d co director ordway research institute professor and director

Drusano GL, SL Preston, C Fowler, M Corrado, B Weisinger, J Kahn

J Infect Dis. 2004;189:1590-1597.


Surrogates antibiotic development14

Surrogates & Antibiotic Development

Can we bridge from mouse to man?

Again, the answer is YES, using Monte Carlo Simulation


Surrogates antibiotic development15

The Reminder Slide

Surrogates & Antibiotic Development

  • The previous data was for resistance, but straightforward cell kill is also possible

  • Later we will see how much kill correlates with what happens in clinical trials

  • BUT, please remember that a total drug AUC/MIC = 88 gives a 2 log kill

Jumbe et al J Clin Invest 2003;112:275-285


Surrogates antibiotic development16

Surrogates & Antibiotic Development

  • So, the exposure target (AUC/MIC) mediating a 2 log10 cfu/g drop in the mouse is identified as the exposure needed to drive a high probability of a good microbiological outcome in patients with nosocomial pneumonia

  • BUT the clinical study was a pneumonia study & the mouse study was mouse thigh infection

  • Andes and Craig showed for a FQ that Mouse thigh and mouse lung targets are virtually identical (AAC 2002;46:1665-1670)

  • How often does a fixed dose of drug achieve this target?


G l drusano m d co director ordway research institute professor and director

Drusano GL, SL Preston, C Fowler, M Corrado, B Weisinger, J Kahn

J Infect Dis. 2004;189:1590-1597.


G l drusano m d co director ordway research institute professor and director

Drusano GL, SL Preston, C Fowler, M Corrado, B Weisinger, J Kahn

J Infect Dis. 2004;189:1590-1597.


Surrogates antibiotic development17

Surrogates & Antibiotic Development

  • So, what do we gain?♦ Information to choose the best dose♦ A high likelihood that the Phase III trial will work (at the cost, that is worth something!)

  • What is there to lose?♦ Nothing that I can see


Surrogates antibiotic development18

Surrogates & Antibiotic Development

  • Let us examine the clinical trial result just presented and speculate about the future

  • We looked at a continuous microbiological variable in the preclinical study and a dichotomous microbiological variable in the clinical study (eradication vs. persistence)

  • Is the microbiological outcome from the clinical trial a surrogate outcome?

  • According to the working group the answer is yes


Examples of laboratory endpoints

EXAMPLES OF LABORATORY ENDPOINTS

THERAPEUTIC BIOMARKER/ CLINICAL

CLASS SURROGATE_OUTCOME

ANTIBIOTICS NEG. CULTURE CLINICAL CURE

ANTI-DIABETIC  BLOOD GLUCOSE  MORBIDITY

LIPID LOWERING DRUGS  CHOLESTEROL  CAD

DRUGS FOR PROSTATE CA  PSA TUMOR RESPONSE

ANTI-HIV DRUGS  CD4; VIRAL RNA DELAY AIDS

From Arthur Atkinson, M.D.


Surrogates antibiotic development19

Surrogates & Antibiotic Development

  • I know it is “the law” that approvals are only given on clinical outcomes, but is it reasonable?

  • Subpart H does existTITLE 21, PART 314, SUBPART HSEC. 314.510 APPROVAL BASED ON A SURROGATE ENDPOINT OR ON AN EFFECT ON A CLINICAL ENDPOINT OTHER THAN SURVIVAL OR IRREVERSIBLE MORBIDITY “FDA MAY GRANT MARKETING APPROVAL FOR A NEW DRUG PRODUCT ON THE BASIS OF ADEQUATE AND WELL-CONTROLLED CLINICAL TRIALS ESTABLISHING THAT THE DRUG PRODUCT HAS AN EFFECT ON A SURROGATE ENDPOINT THAT IS REASONABLY LIKELY … TO PREDICT CLINICAL BENEFIT…”

  • AND, the outcome for pharyngitis is COMPLETELY microbiological in nature

  • So, can trials for approval be smaller, faster, more informative because they are based on microbiological outcomes and still count for NDA submission/approvalThe answer may be addressed in the next talk

  • But, let us examine the issue


Surrogates antibiotic development20

Surrogates & Antibiotic Development

  • Yes, I am a true statistical believer and following to a survivorship endpoint may have the most robustness for being sure that the intervention is doing somethingBUT, antibiotics (and antivirals) are a bit different from other drugs

  • We are NOT docking the drug with a human receptor, but rather the receptor in the pathogen


Surrogates antibiotic development21

Surrogates & Antibiotic Development

  • BIOLOGICAL PLAUSIBILITY

  • EPIDMIOLOGIC EVIDENCE THAT MARKER IS A RISK FACTOR

  • MARKER MUST BE CONSISTENT WITH PATHOPHYSIOLOGY

  • MARKER MUST BE ON INTERVENTION PATHWAY

  • CHANGES IN MARKER REFLECT CHANGES IN PROGNOSIS

  • ADVERSE DRUG EFFECTS MUST NOT BE CONFOUNDING (again, thanks to Dr. Atkinson)

  • So, let us look at microbiological outcome as a surrogate endpointgrowing organisms in sterile areas is a riskthe pathophysiology has the organism at the center of itthe organism IS the target of the interventionmaking it go away improves prognosisadverse drug effects are confounding TO CLINICAL OUTCOME

  • Are there instances where the microbiological effects do not drive outcome clinically?


Surrogates antibiotic development22

Surrogates & Antibiotic Development

  • Sure – nothing is perfect – macrolides and their effects on inflammation may make things better faster clinically in otitis media

  • BUT clinical outcome may also be skewed

  • In pneumonia, the impact of infection on gas exchange may be so far advanced that the drug does its job perfectly (eradicate organisms) but the patient dies of ventilatory failure

  • This is a physiological, NOT drug failure


Surrogates antibiotic development23

Surrogates & Antibiotic Development

  • If the drug does what it is supposed to do can we scientifically impute failure?

  • Currently, this is not THAT big a deal, as clinical outcome and microbiological outcome are tightly intertwined because of the way they are measured

  • Eradication is frequently assessed as a good clinical outcome combined with no chance of primary infection site resampling

  • BUT, it may not always be so


Surrogates antibiotic development24

Surrogates & Antibiotic Development

  • PCR tests, antigen tests, quantitative imaging testing or other methodologies have the possibility of having a quantitative resampling microbiological outcome

  • Dr. Forrest has published a study in which the lower respiratory tract was resampled sequentially

  • Dr. Paul Ambrose has published a quantitative resampling study of sinusitis

  • The future may be now


Surrogates antibiotic development25

Surrogates & Antibiotic Development

  • Look at the results in HIV disease

  • MAJOR advances came about only AFTER quantitative RNA PCR was identified as a valid surrogate endpoint

  • The conversation needs to begin for antibacterials


Surrogates antibiotic development26

Surrogates & Antibiotic Development

  • The insistence on clinical endpoints instead of microbiological endpoints is driven by two things:1) Many statisticians are nihilists – see the silliness of intent-to-treat2) There is a confounding of safety with effectiveness


Surrogates antibiotic development27

Surrogates & Antibiotic Development

  • I believe that we CAN safely use prior information to conduct our clinical trials (In this I am a Bayesian)

  • Nihilistic ITT statisticians say that we need to be ULTRA sure of the validity of the results and, so biological plausibility and prior knowledge need to go out the window

  • The question is: How many times do we reject the true outcome because of statistical nihilism?


Surrogates antibiotic development28

Surrogates & Antibiotic Development

  • What causes more harm?

  • The other issue is confounding endpoints of safety and effect

  • It is true that in HIV disease, patients with MAC had a higher death rate with high dose clarithromycin

  • WHAT IS THE TAKE HOME FROM THIS?

  • In my view, the outcomes should be viewed separately


Surrogates antibiotic development29

Surrogates & Antibiotic Development

  • First, the dose response should be evaluated to ascertain which clarithromycin dose is most effective

  • Second, a safety assessment should be done

  • Here, we would conclude that there were some, but marginal differences in the microbiological activity of high dose clarithromycin

  • However, on the safety evaluation, it had more deaths


Surrogates antibiotic development30

Surrogates & Antibiotic Development

  • Conclusion: The loss of safety with high dose clarithromycin outweighed the minor increase in effect

  • Should a microbiological endpoint ALWAYS be used to measure effect?ANSWER: NO!

  • There are certain instances where there is a high cure rate with no therapy (Polyanna Effect)

  • Use of Time-To-Event analysis with measures of “How do you feel?” endpoints are reasonable


Surrogates antibiotic development31

Surrogates & Antibiotic Development

  • We all know about sinusitis and AEBCB and (in kids) otitis media

  • Sujata Bhavnani, Paul Ambrose and I were recently VERY surprised by the analysis of a CAP trial


Surrogates antibiotic development32

Surrogates & Antibiotic Development

Note 70% probability of cure

at zero drug exposure

These patients were all Fine 1’s and 2’s


Surrogates antibiotic development33

Surrogates & Antibiotic Development

  • In such circumstances, “is your cough or sinus pain or ear ache better?” is a perfectly reasonable approach tied to a time-to-event analysis

  • On the other hand, in patients with VAP with destroyed lung from Pseudomonas exotoxin A getting Ceph du jour, asking about feelings may be impeded by the ET tube and asking the antibiotic to regrow the lungs will be like Waiting for Godot AND IS NOT REASONABLE


Surrogates antibiotic development34

Surrogates & Antibiotic Development

  • We have new tools and better understanding that allows better, more scientific inferences to be drawn without exaggerating risk

  • There are times when evaluation of “how do you feel?” is the most appropriate approach (and makes a heck of a lot more sense than waiting 10-14 days after the sentinel event takes place to make the evaluation)

  • In sick patients, the microbiological endpoint, particularly with resampling makes more sense


Surrogates antibiotic development35

Surrogates & Antibiotic Development

  • In ALL instances, the safety evaluation remains key, but should be done separately

  • Ultimate inferences about the drug, dose and schedule for the indication need to balance safety and effectiveness

  • Let the discussion begin with the regulatory agencies


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