Pharmacodynamics of Fluoroquinolones G.L. Drusano, M.D. Professor and Director Division of Clinical...
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Transcript of Pharmacodynamics of Fluoroquinolones G.L. Drusano, M.D. Professor and Director Division of Clinical...
Pharmacodynamics of Fluoroquinolones
G.L. Drusano, M.D.Professor and Director
Division of Clinical PharmacologyClinical Research InstituteAlbany Medical College &
New York State Department of Health
Pharmacodynamics of Fluoroquinolones
Pharmacodynamics of Fluoroquinolones
• What Pharmacodynamic covariate is linked to outcome?
• Why?• What does this have to do with emergence
of resistance?• What are the factors that amplify resistant
mutant populations?
Pharmacodynamics of Fluoroquinolones
Let us examine fluoroquinolones and determine the pharmacodynamically-
linked variable
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Whi
te B
lood
Cel
l Cou
ntpe
r mm
2 4 6 8 10 12
White Blood Cell Count After I.P. Cyclophosphamide
(100 mg/kg on Day 0 and 75 mg/kg on Day 4 )3
Cyclophosphamide
BacterialChallenge
End ofExperiment
Drusano GL, et al. Antimicrob Agents Chemother. 1993;37:483-490.
Lomefloxacin: Pharmacokinetics and Pharmacodynamics in Septic, Neutropenic
RatsMean Peak Mean AUC Time > MIC
Concentration per 24 h Dosage (mg/L) (mg h/L) (h)
20 mg/kg q6h 4.7 57.2 16.840 mg/kg q12h 6.9 63.6 14.080 mg/kg q24h 20.8 64.3 9.6
For all determinations, N=3. Drusano GL, et al. Antimicrob Agents Chemother. 1993;37:483-490.
Lomefloxacin Therapy for Pseudomonas Sepsis in Neutropenic Rats:
Effect of Dose Fractionation (N=50/Group)
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0 6 12 18 24 30 36 42 48 54 60 66 72
Time (h)
Sur
vivo
rshi
p (%
)
80 mg/kg q24h40 mg/kg q12h20 mg/kg q6hSaline control
Drusano GL, et al. Antimicrob Agents Chemother. 1993;37:483-490.
Lomefloxacin Pharmacodynamics: Survivorship After Challenge (N=20/Group)
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0 8 16 24 32 40 48 56 64 72
Time (h)
Sur
vivo
rshi
p (%
)
40 mg/kg q24h20 mg/kg q12hSaline control
Drusano GL, et al. Antimicrob Agents Chemother. 1993;37:483-490.
Pharmacodynamics of Fluoroquinolones
Sometimes AUC/MIC Ratio is the pharmacodynamically-linked covariate, but sometimes it is Peak/MIC Ratio.
Peak/MIC probably occurs when there are mixtures of sensitive and less-sensitive bacterial populations (more about this anon)
PK/PD Paramters with Fluoroquinolones
• 24-hr AUC/MIC (incorrectly referred to as AUIC) is the parameter that best predicts activity of fluoroquinolones.
• 24-hr AUC/MIC (using free drug levels) for static dose range from 25-50 for most organisms in neutropenic mice
W.A. Craig, M.D.
24-Hr AUC/MIC for Static Doses of Gatifloxacin, Sitafloxacin and Gemifloxacin
Against 6 Strains of Streptococcus pneumoniae24
-Hr A
UC
/MIC
25
50
100
200
GATI SITA GEMI
Total Drug
Free Drug
W.A. Craig, M.D.
Protein Binding Does Matter! - G.L. Drusano, M.D.
Impact of Neutrophils on Activity of
Fluoroquinolones in Mice Based on studies with 2 organisms (K.
pneumoniae and S. pneumoniae) that grow well in normal mice
Neutrophils reduced static doses by 20-40% for K. pneumoniae both in thigh- and lung-infection models
Neutrophils reduced static doses by 75-85% for S. pneumoniae in thigh-infection model
W.A. Craig, M.D.
Pharmacodynamics of Fluoroquinolones
Magnitude of 24-Hr AUC/MIC in serum required for 90-100% survival in animal infection models varies from about 25 in immunocompentent animals for Streptococcus pneumoniae to about 100 in immunocompromised animals for gram-negative bacilli
24-Hr AUC/MIC values of 25 and 100 are equivalent to averaging one and four times the MIC over a 24-hr period
W.A. Craig, M.D.
Relationship Between 24 Hr AUC/MIC and Mortality for Fluoroquinolones in Immunocompromised
Animal Models
W.A. Craig, M.D.
Relationship Between 24 Hr AUC/MIC and Mortality for Fluoroquinolones against
Streptococcus pneumoniae in Immunocompetent Animals
24 Hr AUC/MIC1 2.5 5 10 25 50 100
Morta
lity (%
)
0
20
40
60
80
100
W.A. Craig, M.D.
Pharmacodynamics of Fluoroquinolones
Now that we know what to do for mice and rats, what about clinical
data?
Pharmacodynamics of Fluoroquinolones
Perc
ent o
f Pat
ient
s Rem
aini
ng C
ultu
re-p
ositi
ve
Days of therapy
AUC/MIC <125
AUC/MIC 125-250AUC/MIC >250
100
75
50
25
00 2 4 6 8 10 12 14
Forrest et al
Pharmacodynamics of Fluoroquinolones
• It should be appreciated that this was a retrospective analysis
• Further, the number of patients with Streptococcus pneumoniae infections was ZERO!
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Peak/MIC Ratio
Pro
babi
lity
Levofloxacin Clinical Outcome: Probability of a Successful
Outcome
Patient n=134; 7 Patients FailedMcFadden’s Rho2 = 0.337
Breakpoint = 12.2
Pulmonary Infections (n=87)(500 mg qd)
Skin and Soft Tissue Infections (n=25)(500 mg qd)
Levofloxacin Clinical Outcome: Probability of Successful
Therapy
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 25 50 75 100 125 150 175 200
AUC/MIC Ratio
Pro
babi
lity
Patient n=134; 7 Patients FailedMcFadden’s Rho2 = 0.192
Breakpoint = 50.25
Pharmacodynamics of Fluoroquinolones
• This was the first prospective, multicenter study for the delineation of the linked pharmacodynamic variable for fluoroquinolones
• There was a mix of Gram-negative isolates as well as Streptococcus pneumoniae
• However, the difference in identified breakpoints makes one wonder about the issue of mixed populations of sensitive and less-sensitive pathogens
Pharmacodynamics of Fluoroquinolones
Ambrose PG et al. AAC 2001;45:2793-2797
Pharmacodynamics of Fluoroquinolones
• Clearly, Streptococcus pneumoniae differs from other organisms
• For other pathogens, an AUC/MIC ratio around 100 will produce acceptable response rates
• For S pneumoniae, an AUC/MIC ratio of 20-40 is an appropriate exposure target
Pharmacodynamics of Fluoroquinolones
What about emergence of resistance?
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• Resistance to antimicrobial agents often occurs as a function of single point mutations
• Other mechanisms include spread of plasmids with multiple resistance determinants
• Horizontal transmission also confuses the issue• Examples of a point mutation providing drug
resistance are stable derepression of AMP C beta lactamases for 3rd generation cephalosporins and target mutations or pump upregulation for fluoroquinolones
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• As these occur at a frequency of circa 1/108, infection site populations exceed this frequency, often by multiple logs
• Consequently, such total populations do not behave as a single, sensitive population, but as a mixture of two populations of differing drug susceptibility
• This raises an important question:
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
Can a drug exposure be identified that will prevent the resistant subpopulation from
taking over the total population?
The Team
N. L. Jumbe, A. Louie, W. Liu, M Deziel, V. Tam, T. Fazili, R. Leary, C. Lowry, M.H. Miller and
G. L. Drusano
S. pneumoniae outcome studies
P. aeruginosa outcome studies
Rf in vitro Rfin vivo MIC (g/mL) MBC (g/mL)
2.35x10-6 2.2x10-6 0.8 1.6
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• Clearly, Pseudomonas and Pneumococcus differ in their response
• Pneumococcus has no inoculum effect; Pseudomonas has a major inoculum effect
• The explanation probably rests in the mutational frequency to resistance
• Pseudomonas has a high frequency, while Pneumococcus has a frequency that is not measurable at the bacterial densities used in these experiments with this fluoroquinolone
Peripheral (thigh)Compartment (Cp)
Central Blood Compartment (Cc)IP
injection
kcp kpc
+ Bacteria(XT/R)
f(c)
dCc= kaCa+kpcCp-kcpCc-keCc
dt
ke
dXS=KGS x XS x L - fKS(CcH ) x XS
dtdXR= KGR x XR x L- fKR(Cc
H ) x XR
dt
Kmax CcH
C H
50+CcH
f(CcH)=
Y1=XT=XS+XR
Y2=XR
[4][5]
[6]
[7]
[8]
, =K and = S,R
[2]
L = (1- (XR + XS)/POPMAX)
[9]
dCp = kcpCc - kpc Cp
dt[3]
dCa= -kaCa
dt[1]
KmaxGS
0.117
KmaxGR
0.163
KmaxKS
94.01
KmaxKR
12.16
HKS
6.26
HKR
2.37
C50KS
123.5
C50KR
129.8
KmaxG -maximum growth rate (hr-1) in the presence of drug
KmaxK -maximum kill rate (hr-1)
C50K -drug concentration (g/mL) to decrease kill rate by half
HK -rate of concentration dependent kill
Popmax -maximal population size
Mean Parameter Estimates of the Model.
Popmax = 3.6 x 1010
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• All regimens were simultaneously fit in a large population model
• The displayed graph is the predicted-observed plot for the total population after the Maximum A-posteriori Probability (MAP) Bayesian step
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• All regimens were simultaneously fit in a large population model
• The displayed graph is the predicted-observed plot for the resistant population after the Maximum A-posteriori Probability (MAP) Bayesian step
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• In this experiment, a dose was selected to generate an exposure that would prevent emergence of resistance
• As this was at the limit of detection, the measured population sometimes had “less than assay detectable” for the colony count
• These were plotted at the detection limit
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• We were able to determine how the overall (sensitive plus resistant) population responds to pressure from this fluoroquinolone
• More importantly, we were able to model the resistant subpopulation and choose a dose based on simulation to suppress the resistant mutants
• The prospective validation demonstrated that the doses chosen to encourage and suppress the resistant mutants did, indeed, work
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• Now, for Pneumococcus• We were unable to recover resistant mutants
with levofloxacin as the selecting pressure in the mouse thigh model
• However, we then examined ciprofloxacin as the selecting agent
• Now, selecting mutants was straightforward
Study Design: Mouse Thigh Infection Model- Ciprofloxacin Studies [50mg/kg BID ~
AUC/MIC 100:1]
Begin therapy
Sacrifice, harvest,homogenize muscle
-2 hr 0 hr1. Microbial eradication
2. Selection of resistance
Infect
24 hr
BID
+ 2xMIC Cipro - Drug + 4xMIC Cipro + 3xMIC Levo
Drug #58 RC2
Cipro/±Reserpine 0.6/0.6 3.5/1.0
Levo/±Reserpine 0.6/0.6 0.6/0.6
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• Strain 58, the RC2 and RC4 mutants were sequenced through Gyr A, Gyr B, Par C & Par E.
• The entire open reading frames were sequenced.• No differences were seen between parent and the RC2
daughter strain.• This, coupled with the decrement in ciprofloxacin MIC with
reserpine exposure (3.5 mg/L 1.0 mg/L), implies RC2 is a pump mutant.
• For RC4, a mutation was found in parC (aa 79, sertyr) and this strain also decreased its MIC with addition of reserpine.
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• We have examined other new fluoroquinolones in this system or in our hollow fiber pharmacodynamic system
• All resemble levofloxacin and do not allow emergence of resistance for wild type isolates
• Why is ciprofloxacin different?• Likely because it is the most hydrophilic drug
and is most efficiently pumped by the PMRA pump
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• Hollow fiber System allows simulation of human PK in vitro
• Useful for dose ranging and schedule dependency determinations
• Allows examination of different classes (beta lactams, fluoroquinolones, etc.)
The original hollow fiber system was used by Blaser, Dudley & Zinner
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
Multiple Bacterial Populations Do Make a Difference!
• In Vitro pharmacodynamic model investigations frequently only examine the total bacterial population
• The presence of a small pre-existent population more resistant to the selecting drug pressure has major implications, particularly as the bacterial population size increases to (near) clinical infection size
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
Pseudomonas aeruginosa
Placebo
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0 6 12 18 24 30 36 42 48T ime (h)
Total
ToyamaresistantCiproresistant
Tam et al ICAAC 2001
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
Cipro (AUC/MIC 65.6)
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1
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Time (h)
Total
ToyamaresistantCiproresistant
Tam et al ICAAC 2001
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
T600 (AUC/MIC 3.2)
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0 6 12 18 24 30 36 42 48 T ime (h)
Log1
0 CFU
/mL
Total
Toyamaresistant
Ciproresistant
Tam et al ICAAC 2001
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
T1800 (AUC/MIC 10.4)
01
23
456
78
910
0 6 12 18 24 30 36 42 48 Time (h)
Log1
0 CFU
/mL
Total
ToyamaresistantCiproresistant
Tam et al ICAAC 2001
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
T13500 (AUC/MIC 88.6)
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Time (h)
Total
ToyamaresistantCiproresistant
Tam et al ICAAC 2001
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
T18000 (AUC/MIC 108.3)
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9
0 6 12 18 24 30 36 42 48
Time (h)
Total
ToyamaresistantCiproresistant
Tam et al ICAAC 2001
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
T36000 (AUC/MIC 200.8)
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1
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45
6
7
8
9
0 6 12 18 24 30 36 42 48
Time (h)
Total
ToyamaresistantCiproresistant
Tam et al ICAAC 2001
Central Compartment (Cc)Infusion + Bacteria
(XT/R)
f(c)
dCc=Infusion-(SCl/V)xCc
dt
SCl
dXS=KGS x XS x L - fKS(CcH ) x XS
dtdXR= KGR x XR x L- fKR(Cc
H ) x XR
dt
Kmax CcH
C H 50 +Cc
H f(Cc
H)=
Y1=XT=XS+XR, IC(1)=2.4x108
Y2=XR , IC(2)= 30
[2][3]
[4]
[5]
[6]
, =K and = S,R
[1]
L = (1-X/POPMAX)
[7]
KmaxGS
0.745
KmaxGR
0.614
KmaxKS
27.85
KmaxKR
31.72
HKS
2.24
HKR
3.50
C50KS
16.94
C50KR
107.0
KmaxG -maximum growth rate (hr-1) in the presence of drug
KmaxK -maximum kill rate (hr-1)
C50K -drug concentration (g/mL) to decrease kill rate by half
HK -rate of concentration dependent kill
Popmax -maximal population size
Mean Parameter Estimates of the Bacterial Growth/Kill Model.
Popmax = 3.3 x 1010
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• All regimens were simultaneously fit in a large population model
• The displayed graph is the predicted-observed plot for the drug concentrations after the Maximum A-posteriori Probability (MAP) Bayesian step
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• All regimens were simultaneously fit in a large population model
• The displayed graph is the predicted-observed plot for the total bacterial counts after the Maximum A-posteriori Probability (MAP) Bayesian step
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• All regimens were simultaneously fit in a large population model
• The displayed graph is the predicted-observed plot for the resistant bacterial counts after the Maximum A-posteriori Probability (MAP) Bayesian step
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
P. aeruginosa - Prevention of Amplification of Resistant Subpopulation
• The amplification of the resistant sub-population is a function of the AUC/MIC ratio
• The response curve is an inverted “U”.
• The AUC/MIC ratio for resistant organism stasis is circa 187/1
Tam et al ICAAC 2001
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
P. aeruginosa - Prevention of Amplification of Resistant Subpopulation
Placebo
0
5
10
15
0 12 24 36 48 60 72 Time (h)
Log1
0 C
FU/m
L
Total
Resistant
AUC/MIC 136.7
02468
10
0 12 24 36 48 60 72 Time (h)
Log1
0 C
FU/m
L
Total
Resistant
AUC/MIC 199.7
02468
10
0 12 24 36 48 60 72 Time (h)
Log1
0 C
FU/m
LTotal
Resistant
AUC/MIC 165.8
02468
10
0 12 24 36 48 60 72 Time (h)
Log1
0 C
FU/m
L
Total
Resistant
Prospective Validation
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• This was the same strain as employed in the mouse model, but a different fluoroquinolone
• The mouse model contained granulocytes, while the hollow fiber system does not
• The total drug target for the mouse model was 157 which is a free drug target of 110
• The hollow fiber system target is 187 (1.7 fold )• Craig found that targets increase by 1.5 -2.0 fold
when granulocytes are removed• These results are concordant with this finding
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• Are there other factors that can alter the probability of emergence of resistance?
• The most likely is duration of therapy• Fluoroquinolones induce an SOS response• This resembles a “hypermutator phenotype”• Therapy intensity and therapy duration
should influence the probability of having the resistant population becoming ascendant
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
Emergence of Resistance and the Flight of Time’s Arrow
(Is the duration of therapy important?)
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• A 10 day hollow fiber experiment was performed for MSSA and MRSA (CS) for 6 regimens
• The time to complete replacement of the population with resistant organisms was recorded
• CART was employed to look for a breakpoint in the exposure
• > 200/1 AUC/MIC ratio was identified
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• A stratified Kaplan-Meier analysis was performed with this breakpoint
• The breakpoint was significant (Mantel test p = 0.0007); Tarone-Ware and Breslow Gahan tests were also significant
• To prevent resistance, hit hard (> 200 AUC/MIC) and stop early (< 7 days)
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• The intensity of therapy and the duration of therapy have an impact upon the probability of emergence of resistance
• Short duration therapy trials should examine an endpoint of resistance frequency
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
Targets for Fluoroquinolone Therapy:
Does One Size Fit All?
(A Question Answered in the Affirmative by a Group in the Western Part of New York State -
See an AUC/MIC Ratio of 125)
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
•‘Inverted-U’ Phenomenon
– Resistant sub-populations are initially amplified & then decline with increasing drug exposure 0
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Therapeutic Intensity
Log1
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FU/m
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ResistantSub-Population
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Suppression of Emergence of Resistance: A Pharmacodynamic Solution
P aeruginosa
Log1
0 C
FU/m
L
Daily AUC/MIC
Breakpoint = 187
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Suppression of Emergence of Resistance: A Pharmacodynamic Solution
K. pneumoniae
Log1
0 C
FU/m
L
Daily AUC/MIC
Breakpoint = 93
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Suppression of Emergence of Resistance: A Pharmacodynamic Solution
MSSA
Log1
0 C
FU/m
L
Daily AUC/MIC
Breakpoint = 66
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Suppression of Emergence of Resistance: A Pharmacodynamic Solution
MRSA-CS
Log1
0 C
FU/m
L
Daily AUC/MIC
Breakpoint = 143
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0 100 200 300 400 500
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
MRSA-CR
Log1
0 C
FU/m
L
Daily AUC/MIC
Breakpoint = 484
Suppression of Emergence of Resistance: A Pharmacodynamic Solution
• Some drug exposures allow amplification of the resistant subpopulations
• Exposures can be identified that will prevent this amplification and, functionally suppress emergence of resistance
• The exposures differ by isolate• We can do better in designing doses to not only optimize
outcome, but also suppress emergence of resistance• Attainment of target can be assessed through use of Monte
Carlo simulation