pk/pd - icc - manila, june 5th, 20051 the pharmacological and microbiological basis of pk/pd : why...
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The pharmacological and microbiological basis of PK/PD :
why did we need to invent PK/PD in the first place ?
Paul M. Tulkens
• Cellular and Molecular Pharmacology UnitCatholic University of Louvain, Brussels, Belgium
• Founding member and past-president (1998-2000) of ISAP
www.facm.ucl.ac.be www.isap.org
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The situation in the early 90's …
• anti-infective drug doising was largely irrational or not based on sounds pharmacodynamics / toxicodynamics
• search for low doses for fear of toxicity
• “errors” in drug dosages at registration
• misunderstanding of what is an optimal schedule and what it implies
• pharmacokinetics was mainly used to establish “drug presence” rather than to make true correlations with efficacy
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PK/PD of antiinfectives : what has been done ?
Over the last 10 years, three major concepts have emerged and proven useful :
• dose-effect relationships are not the same for all anti-infectives
• beta-lactams vs. fluoroquinolones or aminoglycosides
• integration of PK/PD within pre-clinical and early clinical development allows prediction of success or failure of new antimicrobials
• PK/PD may help in preventing the emergence of resistance
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PK /PD in action in the Regulatory in the USA
FDA
July 1998
http://www.fda.gov/cder/present/anti-infective798/biopharm/index.htm
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PK /PD in action in the Regulatory in the USA
http://www.fda.gov/cder/present/anti-infective798/biopharm/index.htm
FDA
November 2002
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PK /PD in action in the Regulatory in Europe
" Inadequate dosing of antibiotics is probably an important reason for misuse and subsequent risk of resistance.
A recommendation on proper dosing regimens for different infections would be an important part of a comprehensive strategy.
The possibility of approving a dose recommendation based on pharmacokinetic and pharmacodynamic considerations will be further investigated in one of the CPMP* working parties… "
* Committee for Proprietary Medicinal Products
EMEAJuly 1999
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Publications of the EMEA ...
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The basis of PK/PD
Dosageregimen
Concentrationversus timein serum
Concentrationversus timein tissues andother body fluids
Concentrationversus timeat siteof infection
Pharmacologicor toxicologiceffect
Antimicrobial effect versustime
absorptiondistributionelimination
PHARMACOKINETICS PHARMACODYNAMICS
Craig (1998) CID 26:1-10
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Moving from PK to PD …
Pharmacokineticsconc. vs time
Co
nc.
Time0 25
0.0
0.4
PK/PDeffect vs time
Time
Eff
ect
0
1
0
Pharmacodynamicsconc. vs effect
10-3Conc. (log)
Eff
ect
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Pharmacokinetic/ Pharmacodynamics in Drug Development and Evaluation
The combination of in vitro modelling, proper design of animal model experiments, and the willingness to obtain sparse pharmacokinetic information on patients in clinical trials allows an in depth understanding of which aspects of drug exposure are most closely linked to therapeutic outcome as well as to toxicity.
By providing such information to clinicians, drug therapy can achieve the goal of maximal therapeutic effect while engendering the lowest probability of encountering a drug exposure-related adverse event.
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Main PK/PD properties of antibiotics
Available antibiotic can be divided in 3 groups
• time - dependent (T > MIC)
• AUC / MIC - dependent
• both AUC / MIC AND peak / MIC -dependent
Caveat: this applies to the "clinically-meaningful" concentration window only …
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Cmin Cmax
Cmin Cmax
Clinically-meaningful concentration window …
S. aureus; 24 h
Barcia-Macay et al, submitted; Lemaire et al (2005) JAC
ampicillingentamicin
All antibiotics are concentration-dependent, but it all dependent as how you look at them …
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Antibiotics Group # 1 (after W.A. Craig, 2000; revised 2003)
1. Antibiotics with time-dependent effects and no or little persistent effects
PK/PD parameter
Time above
MIC
Goal
Maximizethe exposure
time
AB
-lactams
* 2d ISAP Educational Workshop, Stockholm, Sweden, 2000; revised accord. to Craig Craig, Infect. Dis. Clin. N. Amer., 17:479-502, 2003* 2d ISAP Educational Workshop, Stockholm, Sweden, 2000; revised accord. to Craig Craig, Infect. Dis. Clin. N. Amer., 17:479-502, 2003
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AB
glycopeptides tetracyclines macrolides streptogramines fluconazole
2. Antibiotics with time-dependent effects, with little or no influence of the concentration BUT with persistent effects
PK/PD parameter
24h AUC / MICratio
Goal
Optimize the quantity of ABadministered
Antibiotics Group # 2 (after W.A. Craig, 2000; revised 2003)
* 2d ISAP Educational Workshop, Stockholm, Sweden, 2000; revised accord. to Craig Craig, Infect. Dis. Clin. N. Amer., 17:479-502, 2003* 2d ISAP Educational Workshop, Stockholm, Sweden, 2000; revised accord. to Craig Craig, Infect. Dis. Clin. N. Amer., 17:479-502, 2003
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AB
aminoglycosides fluoroquinolones daptomycin
3. Antibiotics with concentration-dependent activity and with persistant effects (PAE)
PK/PD parameter
Cmax / MIC and
24h AUC / MICratios
Goal
Optimizeboth the peak
and the quantity
of drug
Antibiotics Group # 3 (after W.A. Craig, 2000; revised 2003)
* 2d ISAP Educational Workshop, Stockholm, Sweden, 2000; revised accord. to Craig Craig, Infect. Dis. Clin. N. Amer., 17:479-502, 2003* 2d ISAP Educational Workshop, Stockholm, Sweden, 2000; revised accord. to Craig Craig, Infect. Dis. Clin. N. Amer., 17:479-502, 2003
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PK / PD in action for the clinics
Some achievements:
• once-daily dosing of aminoglycosides introduced in many countries
• amikacin, netilmicin (from bid to qd)• isepamicin (registered essentially for qd dosing)
• 24h AUC / MIC and Cmax / MIC ratios used as guidesfor phase II / III trials, for treatment optimizationand for registration of new antimicrobials
• moxifloxacin• telithromycin
• dosage of beta-lactams adjusted to cover T > MIC in relation with the expected pathogen…
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PK/PD and resistance …
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0.01 0.10 1.00 10.00
10-2
1
concentration
10-4
10-6
10-8
10-10 MPC 10 = 9
Dong et al; AAC 43:1756-1758
Bactericidal effect of a FQ towards Mycobacterium bovis
Mutant Prevention Concentration …
MIC 99 = 0.8
"Classic" bactericidal effect
Elimination of first mutants
Su
rviv
ing
bac
teri
a
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0.01 0.10 1.00 10.00
10-2
1
concentration
10-4
10-6
10-8
10-10 MPC 10 = 9
Dong et al; AAC 43:1756-1758
Mutant Prevention Concentration …
MIC 99 = 0.8Concentration which will inhibit the majorityof the organisms
Concentration necessary to prevent the selection of the first mutants
Su
rviv
ing
bac
teri
a
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"Window" where selection of mutants takes place …
Time after administration
MIC
MPC
con
cen
tra
tion
MSW
concept from Drlica & Zhao, Rev. Med. Microbiol. 2004, 15:73-80
Mutation selection window
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"Window" where selection of mutants takes place …
MIC
MPC
MSW
No therapeutic effect
Eradication of the first mutants
Selection of the first mutants
Time after administration
con
cen
tra
tion
concept from Drlica & Zhao, Rev. Med. Microbiol. 2004, 15:73-80
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Therefore, new breakpoints for FQ …
Van Bambeke F, Michot JM, Van Eldere J, Tulkens PM. Quinolones in 2005: an update. Clin Microbiol Infect. 2005 Apr;11(4):256-80. PMID: 15760423
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Or, correct assessment of telithromycin…
0
20
40
60
80
100
0.015 0.03 0.06 0.12 0.25 0.5 1 2
Ery-S
MIC (mg/L)
% o
f str
ain
s PK/PD limit of sensitivity (0.25 mg/L)
Ery-r
But MIC90 for Ery-r strains: 0.25-0.5 ...MIC90 for Ery-s strains: < 0.06 ...
Verhaegen & Verbist, Acta Clin. Belg. 2001, 56: 351
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PK/PD in 2005 …
• Use if for efficacy …
• Consider it for avoiding resistance