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Anti-Infective Perspective. Anti-Viral Advisory Committee Meeting July 25th, 2000 Alexander Rakowsky, M.D. Medical Team Leader/DAIDP/ODE4/CDER. Proper Perspective. Focus can be on: new drug development versus changes in dosing/formulation/combinations with approved drugs - PowerPoint PPT Presentation
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Anti-Infective Perspective
• Anti-Viral Advisory Committee Meeting• July 25th, 2000• Alexander Rakowsky, M.D.
Medical Team Leader/DAIDP/ODE4/CDER
Proper Perspective• Focus can be on: new drug development
versus changes in dosing/formulation/combinations with approved drugs
• Focus can be on: systemic agents versus topical agents
• Looking at approved, systemic agents in this presentation
Documents/Guidances
• 1992 Anti-Infectives Points to Consider and also the IDSA/FDA guidances
• Recent re-writes of guidance for various indications
• Clinical Effectiveness Document• Again, focus here is on approved drugs
with changes in dosing/formulation/combinations which lead to a NON-bioequivalent state
Outline of this Talk
• “Don’t kill the messenger”• Brief primer on PK/PD parameters
used in antibacterials (HFD-520 and HFD-590)
• Discussion of how these parameters have or could be used
• Example
Basic DivideCONCENTRATION-DEPENDENT
AUC:MIC Peak Conc:MIC
Fluoroquinolones, aminoglycosides
TIME-DEPENDENT
Time>MIC
Beta-lactams, vancomycin
MIC?????
• “Mean inhibitory concentration” • MBC is similar concept • Based on standardized in vitro work
using specified conditions, growth media, concentrations, nutrient additives for fastidious organisms, etc.
• Reproducibility
MIC?cont
• Difficulty is in interpretation of MIC (S/I/R)
• Based on achievable drug levels (ADME parameters)
• Clinical data is of importance• Defined after discussions by committee
(NCCLS) or review (FDA)• Even then, occasional disagreement
Time-Dependent
• Major parameter is Time>MIC• Based on animal studies (e.g.,
Craig’s work with AOM)• “Confirmed” by clinical trials
Time-Dependentcont
• “Time >” dependent on ADME parameters:– Cmax achieved– distribution of drug (e.g. serum versus
tissue, protein binding, etc.)– half-life of drug (metabolism, excretion)
Time-Dependentcont
• MIC: – pathogen dependent– resistant strains– inoculum effect, effect of pH on activity,
etc.
Time-Dependentcont
• Animal and human studies:– T>MIC in 40-60% range is PREDICTIVE of
clinical success– 100% correlation? NO– Varies also among members of the same
class– Other variables which need to be
accounted for but not as well defined: Post-antimicrobial effect
Concentration Dependent
• Major parameters are Peak:MIC and AUC:MIC ratios
• Animal studies conducted• Human studies done with more
recent FQs (Drusano’s work)
Concentration Dependentcont
• Still dependent on ADME parameters– absorption– distribution– local levels/penetration– local effects (e.g., pH)
– Clinical studies predictive, but again, not 100% correlations.
Conclusions so far
• Variables are based on ADME ranges• Work has shown good
predictiveness but not 1:1 correlation • Variability in the MICs• Most work done on beta-lactams and
FQs
So What is the Role of PK/PD?
• Several recent meetings to discuss:– DAIDP Advisory Committee: 7/98 and 10/98– July 1998: FDA/Industry meeting– March 1999: FDA/ISAP Workshop
– ISAP: The International Society of Anti-Infective Pharmacology
Other Difficulties Raised
• Emphasis has been on effectiveness,not safety
• Most work done with single drug/bug• Acute models used (chronic
use/chronic illness not well studied)• Moving targets (resistance
development), esp. with chronic use, use over time
Is All Lost?
• Overall, positive impressions– PK/PD for certain antimicrobial drug
classes is well worked out–Models used (both animal and human)
are improving greatly– Can be seen, in the proper context, as
strong supportive evidence
Coming Full Circle• Augmentin 7:1 NDAs (submitted in
1994/1995)• Adults: 500 mg tid to 875 mg bid of
amoxicillin and 250 mg tid to 500 mg bid• Pediatrics: 40/mg/kg/day divided tid to 45
mg/kg/day divided bid of amoxicillin• In all formulations, clavulanic acid amount
remained the same. Led to 1/3rd less daily clavulanate
Augmentin (cont)
• In all settings, AUC and half-life comparable between new and old dosing regimens
• Cmax higher by 50-80% in bid dosing regimens• T>MIC lower in bid regimens– on average, bid regimens with 10 hours (out of 24)– on average, tid regimens with 11 hours (out of 24)– concerns also with 1/3rd lower beta-lactamase
inhibitor activity
Augmentincont
• Post-antibiotic and post-beta-lactamase inhibitor effects were studied and proposed
• Animal studies showed comparable efficacy rates for the bid and tid dosing regimens
• Due to concerns with lower T>MIC and clavulanic acid, clinical studies were asked for
Augmentincont
• One study per indication was conducted (historically, two would have been required)
• NDAs were approved based on:– in vitro microbiology and animal work– PK/PD data from humans– one adequate, well-controlled study per
indication– agreement to study as q12 not bid
Augmentincont
• Ultimately these NDAs were approved with approximately 50% less subjects enrolled then historically required
• See this as a good example of where/how PK/PD parameters can be used
Conclusions• Certain parameters/drug classes well
worked out• Still issues with variability (with ADME
parameters, MICs, local effects, etc.)• Multiple meetings held where, at this time,
PK/PD is seen as strong supportive evidence but that for reasons listed, should not be used in lieu of clinical evidence