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Pharmacodynamics of antibiotics:Correlation between kinetics and activity
Paul M. Tulkens
Cellular and Molecular Pharmacology Unit
& Centre for Clinical Pharmacy
Catholic University of Louvain, Brussels, Belgium
International Society for Anti-infective www.facm.ucl.ac.be www.isap.org
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 1
International Society for Anti-infective
Pharmacology (ISAP)
www.facm.ucl.ac.be www.isap.org
Pharmacodynamics of antibiotics:Correlation between kinetics and activity
• Rising resistance and correlation with antibiotic use …
• Did we use antibiotics in a rational way ? …
• What is pharmacodynamics and how can it help you ? …
• Can we prevent (or slow down the emergence of) resistance ? …
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 2
www.facm.ucl.ac.be
• Can we prevent (or slow down the emergence of) resistance ? …
• Can we also reduce health care costs ? …
www.isap.org
Resistance is the problem …
20
25
30
35
40
pe
rce
nta
ge
penicillin* intermediate
tetracyclines
macrolides
penicillin* full resistant
1/3 patients
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 3
0
5
10
15
85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 20
year
pe
rce
nta
ge
Belgian Reference Laboratory for pneumococci, Leuven, 2000
1/5 patients
* all β-lactams (= penicillins, cephalosporins, …)
Overuse is also the problem …
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 4
Risk of resistance to ββββ-lactams among invasive isolates of Streptoccus pneumoniae regressed againstoutpatient sales of beta-lactam antibiotics in 11 European countries• resistance data are from 1998 to 1999; antibiotic sales data 1997. • DDD = defined daily doses
Bronzwaer SL, Cars O, et al. Emerg Infect Dis 2002 Mar;8(3):278-82
How can you be "better" ?
• be globally efficacious
� pharmacodynamics (PK/PD)
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 5
• avoid selection of resistance
� "mutant prevention concentration"
What is Pharmacokinetics / Pharmacodynamics
(PK/PD) ?
• Pharmacokinetics:
what the body does to the drug
� absorption, distribution, serum and tissue levels elimination, …
dose and
schedule
Cmax
t1/2
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 6
• Pharmacodynamics (of AB):
what the drug does to the bacteria
� static vs. bactericidal effect, rate of kill, eradication, prevention of resistance….
clearance
• Emax
• time to Emax
• prevention of
relapses
• maintenance of
susceptibility
The problem as seen from a question of the FDA...
Same dose ??
And what about those ones ?
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 7
Breakpoints tend to set up quantic limits in what is fundamentally a continuous distribution ...
What are "Pharmacodynamic indices" ?
• all drugs have pharmacokinetic properties that describe
the way the body handles them
– antibiotics are no exception …
– you need to consider the Cmax and the clearance (that will result in
a given half-life) to describe the drug exposure
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 8
• a drug needs to bind to its target to act …
– antibiotics are again no exception, but the target is the bacteria …
– the antibiotics can be studied in vitro to look at the extent of their
action at increasing concentrations (like the binding of a ligand to
its receptor in conventional pharmacology). This is
drug pharmacodynamics…
Pharmacokinetics ���� Pharmacodynamics...
Pharmacokineticsconc. vs time
Co
nc.
Time0 25
0.0
0.4
Pharmacodynamicsconc. vs effect
10-3Conc. (log)
Eff
ect
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 9
PK/PDeffect vs time
Time
Eff
ect
0
1
0
Time 10Conc. (log)
Example of a pharmacodynamic relationship
Emin
Emax
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 10Barcia-Macay et al. Antimicrob. Agents Chemother. 2006; 50(3):841-51
MIC
And what if we put pharmacokinetics ?
Emin
Emax
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 11
MIC
Cmin-Cmax
Barcia-Macay et al. Antimicrob. Agents Chemother. 2006; 50(3):841-51
And what if we put pharmacokinetics ?
low concentration dependency
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 12
Cmin-Cmax
high concentration dependency
Barcia-Macay et al. Antimicrob. Agents Chemother. 2006; 50(3):841-51
From Pharmacokinetics to Pharmacodynamics of AB …
Peak / MIC
AUC / MIC
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 13
Time > MIC
AUC / MIC
A simple dynamic model …
Drug Conc.
Inflow = Clearance
Fresh
MediumWaste
Pump
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 14
AUC
TimeV
T1/2 = 0.693 * V/Cl
Sampling of
Drug, Bacteria
Adapted from M.N. Dudley, ISAP / FDA Workshop, March 1st, 1999
Peak
Pharmacodynamics: the basic question …
Which antibiotics are
• time-• AUC• peak-
dependent
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 15
in clinically meaningful
conditions ?
• peak-
Available antibiotics can be divided in 3 groups :
• time - dependent (T > MIC)
• AUC / MIC - dependent
Main PK/PD properties of antibiotics
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 16
• AUC / MIC - dependent
• both AUC / MIC and peak / MIC -dependent
Antibiotics Group # 1 (after W.A. Craig, 2000; revised 2002 and 2003)
1. Antibiotics with time-dependent effects and no or little persistent effects
PK/PD parameter GoalAB
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 17
PK/PD parameter
Time above
MIC
Goal
Maximalizethe exposure
time
AB
β-lactams time above the MIC
How long should you stay above the MIC ?
• cefotaxime
• neutropenic mice
• K. pneumoniae
40 %
Moderate infections
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 18
• K. pneumoniae
• lung infection
100 %
Serious infections
Do all β-lactams have similar PK/PD properties ?...
different pathogens
• same shape of
dose response
• diff. In T > MIC
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 19
• diff. In T > MICfor a static effect
(penicill. > carbap.)
• diff Emax
(penicill. < carbap.)
Andes & Craig Int. J. Antimicrob. Agents 2002, 19: 261-268
Dosing amoxycilline for respiratory tract infections in Belgium
Sensitivity of S. pneumoniae to amoxycillin
cu
mu
lati
ve %
of
str
ain
s
75
100
1000 mg3 x / j
500 mg
Dose and schedule for T > CMI = 50 %
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 20
CMIMIC data: J. Verhaegen et al., 2001
cu
mu
lati
ve %
of
str
ain
s
0.01 0.10 1.000
25
50500 mg3 x / j
500 mg2 x / j
S I R
Antibiotics Group # 2 (after W.A. Craig, 2000; revised 2002 and 2003)
2. Antibiotics with time-dependent effects, no or little influence of concentration, but marked, persistent effects
PK/PD parameter GoalAB
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 21
PK/PD parameter
AUC / MIC
Goal
optimize the amount of
antibiotic
AB
glycopeptides
tetracyclines
macrolides
linezolid
streptogramins
Antibiotics Group # 3 (after W.A. Craig, 2000; revised 2002 and 2003)
3. Antibiotics with concentration-dependent bactericidal activity and prolonged persistent effects (post-antibiotic effects)
PK/PD parameter GoalAB
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 22
PK/PD parameter
Peak andAUC / CMI
Goal
optimize the peak and
the amount of antibiotic
AB
aminoglycosides
fluoroquinolones
daptomycin
ketolides
Aminoglycosides: get a peak !
1. Appropriate mode of
administration
IV route
2. Calculation of the necessary
peak value
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 23
peak value
minimal peak: = MIC / 8
3. Calculation of the adequate dosis
peak = dosis / Vd
dosis = peak x Vd
dosis = MIC x 8 x Vd
Aminoglycosides: why a peak ?
Aminoglycosides are concentration-dependent
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 24
concentration-dependent drugs in the clinically meaningful concentration range ...
Aminoglycosides: why a peak ?
Clinical efficacy
is linked to
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 25
is linked to
peak/MIC ratio
Fluoroquinolones: get a peak and an AUC !C
on
cen
trati
on
increase the amount administered,
in order to optimize AUC/MIC
and peak/MIC
should be > 125 *
should be > 10
Get both a peak and a AUC !!
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 26
Time (h)
Co
ncen
trati
on
MIC
Why an AUC / MIC > 125 for fluoroquinolones ...
AUC / MIC
is
one parameter …
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 27
Forrest et al., AAC, 1993
one parameter …
What do you mean by PEAK /MIC > 10 and AUC / MIC > 100
low ratioMIC
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 28
high ratio
AUC24h = dose / clearance
MIC
AUC/MIC24h =125 : a magical number??
125 was the limit below which failure
rates became unacceptable because of
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 29
rates became unacceptable because of
either
• a large MIC
• or a too low dosage (AUC is proportional to the dosage)
Is 125 good for all ??
80
100
Perc
ent m
ort
alit
y
Mo
rtali
ty (
%) 80
100
The saga of S. pneumoniae ...
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 30
3 30 30010 100 1000
0
20
40
60
24 hr AUC/MICP
erc
ent m
ort
alit
y
neutropenic
Emax at
125 ...
24 Hr AUC/MIC
Mo
rtali
ty (
%)
1 2.5 5 10 25 50 100
0
20
40
60
non-neutropenic
Emax at
30 ...
How to optimize the AUC / MIC ratio ?
AUC = dosis / Cl
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 31
Adjust the daily dosis
~ target AUC
Adapt the number of administrations
~ pharmacokinetics of the drug
10-2
1
10-4
10-6
Mutant Prevention Concentration …
"Classic" bactericidal effect
Su
rviv
ing
bacte
ria
MIC 99 = 0.8
poorly sensitive organisms…
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 32
0.01 0.10 1.00 10.00
concentration
10
10-8
10-10 MPC 10 = 9
Dong et al; AAC 43:1756-1758
Elimination
of resistant
organisms
Su
rviv
ing
bacte
ria
10-2
1
10-4
10-6
Mutant Prevention Concentration …S
urv
ivin
g b
acte
ria
MIC 99 = 0.8
Concentration which
will inhibit the majority
of the organisms
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 33
0.01 0.10 1.00 10.00
concentration
10
10-8
10-10 MPC 10 = 9
Dong et al; AAC 43:1756-1758
Su
rviv
ing
bacte
ria
Concentration
needed to
prevent the
selection of
resistant
organisms
"Window" where selection of mutants/resistants may take place …
MPC
co
nce
ntr
atio
n
Mutation selection window
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 34
Time after administration
MIC
MPC
co
nce
ntr
atio
n
MSW
concept from Drlica & Zhao, Rev. Med. Microbiol. 2004, 15:73-80
Which are the MPC values compared to
- MIC for S. pneumoniae
- Cmax for a standard dose ?
Molecule MIC MPC
levoflox. 1 8
Cmax
≈ 6(500 mg)
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 35
levoflox. 1 8
moxiflox. 0.25 1
Adapted from D. Croisier, 2005, Bondeau et al., 2001, and Hansen et al, 2003
≈ 6
≈ 4
(500 mg)
(400 mg)
So, let us accept values with some degree of precaution
If you wish to prevent resistance
� peak / MIC > 10
(which covers the MPC)
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 36
(which covers the MPC)
If you believe your patient is not a
healthy mouse …
� AUC24h / MIC > 100
A proposal for PK/PD based-breakpoints for fluoroquinolones...
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 37
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
PK/PD in action …
Levofloxacin 500 mg
1X / jr
• AUC [(mg/l)xh] 47
• peak [mg/l] 5
� MICmax < 0.5
Moxifloxacin 400 mg60
80
100
% of sensitive strains
moxi
PK/PD breakpoint
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 38
Moxifloxacin 400 mg
1X /jr
• AUC [(mg/l)xh] 48
• peak [mg/l] 4.5
� MICmax < 0.50
20
40
60
0.015 0.03 0.06 0.125 0.25 0.5 1 2 4
MICMIC data: J. Verhaegen et al., 2003
levo
A clinical algorithm ...
Knowledge or ou “educated” suspicion of the causative agent
Pathology andepidemiology
Local MIC data
Is the organism probably highly
susceptible ?
noyes
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 39
susceptible ?
Obtain an MIC
Use common dosage but with attention to PK/PD
Adjust the dosage on a full PK/PD basis
S / I / Ris
insufficient !!
Success ?
re-evaluate• the dosage
no
Consider
yes
A clinical algorithm (follow.) ...
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 40
• the dosage• the therapeutic scheme• the antibiotic classbased on PK/PD properties
step-down therapyif acceptable on a microbiological
point of view
Use these pieces of information to establish recommendations based on local epidemiology and on the knowledge of the
PK/PD properties and of the risk for resistance
And what about health care costs ?
Pharmacoeconomics
Economic
• cost minimization
• cost benefit
• cost effectiveness
Humanistic
• quality of life• patient's preference
• patient's satisfaction
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 41
• Pharmacoeconomics of antibiotics is still largely underdeveloped outside the USA
(but US-based models cannot easily be applied);
• However, comparisons identifying differences in
– amount of money needed to reach a given (better ? ) clinical outcome;
– expenses related to the same (or better) quality of life and patient's satisfaction;
may already suggest interesting avenues for further fine-tuning therapeutic guidelines
• cost effectiveness• cost utility
• patient's satisfaction
L. Sanchez, In Pharmacotherapy, DiPiro et al. eds, p.2, 1999
Rational bases for the choice of an antibiotic
• Know your LOCAL epidemiology
� obtain MIC distributions from your microbiologists…
• know the PK profile of the drugs you consider to purchase
�aim at obtaining > 90 % efficacy against the organisms of interest (AUC, peak, time above MIC) with a standard dosage, …
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 42
dosage, …
• include a safety margin (MPC …)
• Compare products on that basis first …
• Remember that
• no antibiotic (if possible) is the best…
• but that treatment failures (when treatment is needed) cost a lot …
Please, act …
W.A. Craig, MDM.N. Dudley, Pharm.G.L. Drusano, MDJ.J. Schentag, Pharm.A. McGowan, MDX. Zao, PhD
Tunis - 18-04-06PD of antibiotics: correlation between kinetics and activity 43
www.antiinfectieux.org
F. Van Bambeke, Pharm.A. Spinewine, Pharm.S. Carryn, Pharm.H. Chanteux, Pharm.H. Servais, Pharm....
X. Zao, PhDV. Firsov, MDS. Zinner, MDA. Dalhoff, PhD...
www.isap.org
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