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1
Rationale for the effective use of pharmacokinetics and
pharmacodynamics in drug development
P.L. Toutain
ECOLENATIONALEVETERINAIRE
T O U L O U S E
Update: 09/10//2010
2
Objective of the presentation
• To show non-kineticists that PK can be a
very useful tool to document drug safety
and efficacy
• To understand the meaning and utility of the
main PK parameters
3
PHARMACOLOGY
Pharmacokinetics
Pharmacodynamics
Clinical pharmacology
Action of animal on drug
Action of drug on animal
Study of drug in a clinical context
4
Clinical trialsvs.
PK/PD trials
5
Dose titration
Dose ResponseBlack box
PK/PD
Dose
PK PD
Plasmaconcentration
surrogateResponse
6
Dose effect vs. concentration effect relationship
DOSE AUC = (Dose/Cl)
EFFECT EFFECT
Less variance must be expected in the AUC/effect than in the dose/effect relationship
External dose Internal dose
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Acute toxicity of anticancer drugshuman versus mouse
0
2
4
6
8
10
12
14
0-1 0.4-0.6 0.6-1.2 2.0-3.0 >4 0
2
4
6
8
10
12
14
0-1 0.4-0.6 0.6-1.2 2.0-3.0 >4
Dose RatioExternal dose
AUC Ratio Internal dose
Fre
qu
ency
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Digoxin levels in toxic and nontoxic patients
* From smith TW and haber E. J clin invest 1970;49:2377-86.
Non toxic (131)
Toxic (48)
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The concentration principle in drug development:
Extrapolations
• From in vitro to in vivo
• From experimental to target species
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PK/PD: in vitro vs. in vivo
ResponsePlasmaconcentration
Body
Medium concentration Test system
effet
In vivo
In vitro
Extrapolation in vitro in vivo
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The concentration principle in drug development: mechanistic approach
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PK/PD: mechanistic approach
PK/PD
DoseResponse
PK PD
Plasmaconcentration
Plasma concentration
Drug receptor interaction
TransductionDose
Response
Drug specificity, affinity &intrinsic efficacy
System specificity
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Dose vs. plasma concentration profile as independent variable
Dose
Mass(no biological information)
Dose F%Clearance
Time
Concentration profile
X
(biological information)
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PK vs. PD variability
i.e. the 2 main sources of variability
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PK and PD variability
well documented– species– food– age– sex– diseases
PK PD
Dose
Plasma concentration
EffectBODY Receptor
Generally ignoredbut usually more
pronounced than PK variabilities (for a given
species)
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Coefficient of variation (%)
PK PD
Clearance Vss EC50 EC50
antipyretic anti-inflammatory
Nimesulide 17 20 49 62
Tolfenamic Ac. 28 9.5 47 48
Prednisolone 12 15 49
PK/PD variability for anti-inflammatory drugs
T. Haake, 1997
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Definition of the main pharmacodynamic drug properties
• Efficacy– Drug action, drug effect, drug response– efficiency
• Potency– Power
• Sensitivity• Selectivity• Specificity
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The 3 structural parameters of the dose-effect relationship
Emax ED50slope
shallow
steep
ED502
Emax 1
Efficacy Potency Sensitivity
Emax 2
1
2
12
ED501
Range of useful concentrations Selectivity
2
1
25
Efficacy vs. potency and selectivity
• Efficacy, potency and selectivity therapeutic effect
side effect
A more potent than BA = B for efficacyB is preferable to A in a clinical context for its selectivity
A B
Concentration
Eff
ect 100
80
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PK/PD variabilitiy
• Consequence for dosage adjustmentPK PD
Dose
Plasma concentration
EffectBODY Receptor
Kidney functionLiver function...
Clinical covariables• disease severity or duration • pathogens susceptibility
Population approach
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Kinetic population vs. classical approach
• Subjects
• Location of study
• Sampling
• Subject homogeneity
• Controlled variable
• Inference space
Classical
Few (healthy)
laboratory
intensive
yes
yes
narrow
Population
Many (patient)
hospital
sparse
no
no (but documented)
large
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What is the usefulness of PK
A scientific toolR & D
Scientific critical mass of the company
Can be very sophisticated
A requirement for regulatory affairs
Guidelines
Very basic
Drug monitoring
Human medicine
Drug submissionDrug discovery and
developmentDrug prescription
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Usefulness of PK
1-Drug prescription
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Drug candidates for Therapeutic Drug Monitoring (TDM)
• Low therapeutic index
• No physiologic or therapeutic endpoints to guide dosage
• Pharmacokinetics vary widely between individuals
• Need to monitor adherence ?
32
Effect of adherence rate on outcome in HIV infected patients
From: Paterson DL, et al. Ann Intern Med 2000;133:21-30.
33
Usefulness of PK
2-Drug discovery
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Drug discovery and PK
• The success rate of New Chemical Entities (NCE) is low (1/5000)
• The main reasons for failure were :
– unacceptable clinical efficacy
–Historically poor PK (40%) but much better now
35
Why compounds fail or slow down in development
37
Drug discovery strategies
• Researchers have concentrated on maximizing potency and selectivity (specificity) against a biological target
but
• a good candidate requires a balance of potency, safety and PK properties
now:
• drug metabolism and PK in drug discovery process is accepted
41
Hierarchical in vitro screening sequences
New compound(s)
In vitro binding against target receptor
In vitro binding against selectivity receptors
Functional activity against target receptor
In vitro intrinsic clearance in hepatocytes
In vitro permeability in Caco-2 cells
In vitro protein binding
In vivo pharmacokinetic and pharmacodynamic evaluation
Physiochemical analysis; measured or computed
Roberts S.A. Current opinion, Drug Disc. Dev. 2003,6: 66-80
42van de Waterbeemd & Gifford, Nature Reviews Drug Discovery 2, 192, 2003Predictive models ADME processes Predictive models ADME processes
43
Clearance
HepaticRenal
Metabolic Biliary
CYP450 Others
Polymorphism 1A2;2C9;2C19;2D6;3A4
IR
InductionInhibition
CAR
AHRPXR
Sulfate
GlucuronideAmino-acid
44
• PK (clearance determination) is the bottleneck
cocktail approach
and
cassette dosing
• Objectives– 200 compounds per week for 2 scientists
Pharmacokinetics and combinatorial chemistry
48
Possible Impacts of MW
Size or molecular weight of a potential drug affects:
1. stability, ease of synthesis?2. solubility, transport across membranes3. bioavailability 4. Biliary excretion (interspecific differences)5. Safety (antigenicity)6. success in clinical trials 7. FDA approval!
52
Usefulness of PK
3-Regulatory pharmacokinetics
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Regulatory pharmacokinetics
• Purpose
– Necessity to understand the role of regulatory authorities
– The role of the authorities is to ensure that marketed drug products are safe and effective
– The authority requires basic PK information to understand the features of the drug and factor variation
55
Regulatory pharmacokinetics
• Guideline vs. science driven PK– the PK guidelines were written to provide regulatory
people with the minimal information required to make a judgment and not to provide companies with an optimal drug development procedure
– Some companies have forgotten the true purpose of PK studies and too often PK data appear to have been generated with a "checklist" for regulatory authorities in mind rather than a scientific approach to efficacy
56
In a company, is PK conducted as :
A regulatory requirement
or
For rationale drug development
57
If PK is scientifically conducted
10 critical PK and PD parameters should be determined for each new drug
58
Hierarchy of pharmacokinetic parameters
R & D• Clearance• Effective concentration range• Extent of bioavailability• Fraction of the available dose excreted
unchanged• Blood / plasma concentration ratio• Half-life• Toxic concentration• Extent of protein binding• Volume of distribution• Rate of availability
Regulatory• Absorption• Distribution• Metabolism• Elimination
Benett, 1993
59
Hierarchy of pharmacokinetic parameters
R & D
• Independent
• Have a physiological meaning
• Clearance, distribution
Regulatory affairs
• Hybrid
• Only descriptive
• t 1/2, Cmax, Tmax