Issues in development for an MDR TB indication

Leonard Sacks MDDivision of special pathogens and transplant products

FDA

Pros and cons in developing drugs for MDR TB

• Area of pressing medical need• Drug effect potentially very

obvious (e.g. in patients with positive sputum despite years of MDR therapy)

• Effectively may resemble monotherapy if other drugs have failed

• May be faster than demonstrating efficacy in drug sensitive patients (Analogous to EBA)

• Accelerated approval

• MDR TB is not a homogeneous disease

• Definitions of resistance vary-clinically, microbiologically

• Treatment regimens are complex

• Monotherapy is not a viable approach

• Reliability of sputum conversion as a surrogate for clinical outcome is not clear.

Traditional efficacy studies

ARM A• Drugs ABCD• 95% Success

ARM B• Drugs ABCX• 96% Success

Just to see a failure, we need many patients per armTo compare these small differences with confidence we need a large studyIn this non-inferiority model, the effect of drug X may be masked by the rest of the regimen

MDR study

ARM A• Optimized

background• Success 3%

ARM B• Optimized

background + X• Success 40%

In this study, only a handful of patients are needed to show superiority

The drug effect is almost entirely attributable to drug X

Past experience with drugs for resistant conditions

How have we dealt with resistance in the past?

• MDRSP

• VRE

• MRSA

• Resistant HIV

• Cancer resistant to chemotherapy

MDR S Pneumoniae

• Established efficacy for drug sensitive S. pneumoniae in randomized controlled blinded studies.

• Micro evidence of activity in MDRSP

• Independent mechanism of action

• Clinical success in 15 cases of pneumonia due to MDRSP

MDR S Pneumoniae

Source: product label

Vancomycin resistant enterococcus

Synercid- • for Vancomycin resistant E fecium bacteremia• for complicated skin and skin structure infection

– two comparative trials in complicated skin infections– no primary efficacy demonstrated in drug-sensitive

enterococcal infection– Drug was approved based on subpart H using

clearance of bacteremia as a surrogate for clinical outcome. Data from four non-comparative studies in 1222 patients with VRE bacteremia

Vancomycin resistant enterococcus

Linezolid-

• Randomized double blind studies for the following:– VRE infections, – pneumonia– skin infections

Linezolid- dose ranging study for VRE

Source: product label

Resistant HIV

• Tipranavir– For combination ARV use– For highly treatment experienced patients or virus

resistant to multiple protease inhibitors

• Approval based on viral suppression at 24 weeks

Tipranavir clinical studies

Source: Product label

Some points on clinical drug development for resistant infections• Generally, initial development for drug

sensitive disease

• Controlled data in resistant infections

• Dose response in resistant infections

• Data in resistant infections with historical controls

• Tipranavir is the closest model addressing the issue of combination therapy

Quinolones for MDR TB

Quinolones

• What have we learned about quinolones and resistant TB?

• In vitro– MIC– Mechanism of action

• Animals• Human (retrospective)

– EBA– Non-comparative– Comparative

• Historical

QuinolonesMICs

In vitro and in vivo activities of Moxifloxacin and clinafloxacin against MTB Ji B. Lounis N, Maslo C, Truffot-Pernot C, Bonnafous P, Grosset J Antimicrob, agents and chemo 1998;42:2066-2069

MICs to 15 drug-sensitive and 5 MDR strains

MICs to 18 drug-sensitive strains

In vitro and in vivo activities of Levofloxacin against MTB Ji B. Lounis N , Truffot-Pernot C, Grosset J Antimicrob, agents and chemo 1995;39:1341-1344

Quinolones animal models

Mouse 30 day survival rates after IV infection with H37Rv

(Rx day 1-28)

In vitro and in vivo activities of Moxifloxacin and clinafloxacin against MTB Ji B. Lounis N, Maslo C, Truffot-Pernot C, Bonnafous P, Grosset J Antimicrob, agents and chemo 1998;42:2066-2069

QuinolonesHuman EBA data

The bactericidal activity of moxifloxacin in patients with pulmonary tuberculosis R Gosling, L Ulso, N Sam, E Bongard, E Kanduma, M Nyindo, R Morris, S Gillespie. Am J Respir Crit Care Med 2003;168:1342-1345

5 day EBA

QuinolonesHuman data

– Retrospective (historical controls)– MDR cure rate (1973-1983) 56%– MDR cure rate (1984-1998) 75%– Treatment and outcome analysis of 205 patients with multidrug resistant tuberculosis Chan E, Laurel V.

Strand M. Chan J. Huynh M, Goble M, Iseman M Am J respir Crit Care Med 2004, 169:1003-9

QuinolonesHuman data

Survival (TB related) – quinolones versus no quinolones

•Retrospective (Not randomized)

•Confounders- surgery

Thoughts on study design for drugs to treat MDR TB

Study populations

• Primary MDR– disease more homogeneous– Very low rates in US- target high risk areas e.g. Estonia

• Secondary MDR– Typically extensive cavitation and fibrosis– Surgery often needed– Problem of drug entry into fibrotic lesions– Patients usually well known to clinics

• HIV MDR– Outbreak setting - probably less appropriate

• Number of drugs to which resistance is documented 2, 3 or 7?

• Extent of disease- cavitation, fibrosis, extent

Entry criteria

• establishing resistance

• documenting persistent positive cultures despite prior therapy.

Study arms

• The need for not one but two or more new agents

• Have we reached the point where we can compare a new MDR drug cocktail with a quinolone cocktail?

Traditional approach to a resistance claim

• Establish microbiological efficacy for resistant organisms

• Identify independent mechanism of action• Demonstrate similar in vitro MICs for drug

sensitive and MDR strains of the organism• Establish efficacy in drug sensitive

infection (randomized controlled trials)• Limited treatment experience in MDR

cases

Beginning of the road model

• Primary resistance to Rifampin and INH usually determined from baseline culture about 1 month after starting therapy

• Not always identified as clinical drug failure. Some respond to initial therapy though response may be slower (median 2 months)

• preferable to enroll those with positive sputum culture after 1 month (at initiation of therapy for resistant infection)

Possible schema for studying 2 rifampin and INH resistance

Smear positive

after 30 days INH and Rifampin resistance determined

smear positive smear negative

New drug + second line drug ?quinolone + second line drug

When 1 month cultures available those with a negative culture are excluded from efficacy analysis

End of the road model

• Patients with 6 or 7 drug resistance and persistent sputum positivity

• In such individuals, a drug with a novel target, good micro against MDR, MDR animal models, volunteer safety data, limited human data on comparative sputum conversion rates could conceivably lead to a limited approval.

Possible schema for studying high grade MDR

Known high grade MDR

3 months treatment failureCulture positive

Background + New drug Background + placebo

Alternatives to placebo include

•dose ranging,

•immediate versus delayed dosing,

•historical control data with predetermined minimal efficacy standard

End of the road

“Reverse EBA”

Drug first

Placebo first

%Culture positive

Days

• Where the drug is very efficacious, small numbers of patients would be needed to show efficacy

Conclusions

• There are several precedents for development of drugs for resistant infection

• MDR may provide an opportunity to demonstrate the efficacy of new anti-TB agents in small numbers of patients

• Several study designs are possible• MDR studies may be conducted in parallel

with studies in drug sensitive disease