Pharmacodynamics of Antimicrobialsin Animal Models

William A. Craig, M.D.

University of Wisconsin-Madison

0 2 4 6

2

4

6

8

18.8 mg/kg 4.7 mg/kg 1.17 mg/kg

0 2 4 6

40 mg/kg 10 mg/kg2.5 mg/kg

0 2 4 6

40 mg/kg 10 mg/kg 2.5 mg/kg

CFU = colony-forming unit.

Craig WA, et al. 40th ICAAC Toronto, Ontario, September 17-20, 2000.

Telithromycin Azithromycin Clarithromycin

Time (hours)

Lo

g10

CF

U p

er T

hig

hEffect of Increasing Concentrations

on Killing of Pneumococci in Thighs of Neutropenic Mice

In Vivo PAE for Azithromycin with Streptococcus pneumoniae ATCC

10813 in Thighs of Neutropenic Mice

Time (Hours)

0 2 4 6 8 12 18 24

Lo

g 10 C

FU

/Th

igh

3

4

5

6

7

8

9

10

ControlAzi 8 mg/kg

PAE = 11.0 Hrs

T>MIC

Patterns of Antimicrobial Activity

Concentration-dependent killing and prolonged persistent effects

Seen with aminoglycosides, quinolones, daptomycin, ketolides, amphotericin B and echinocandins

Goal of dosing regimen: maximize concentrations

AUC/MIC and Peak/MIC major parameters correlating with efficacy

Patterns of Antimicrobial Activity

Time-dependent killing and minimal or no persistent effects

Seen with all beta-lactams and flucytosine

Goal of dosing regimen: optimize duration of exposure

Time above MIC major parameter correlating with efficacy

Patterns of Antimicrobial Activity

Time-dependent killing and moderate to prolonged persistent effects

Seen with macrolides, azithromycin, clindamycin, tetracyclines, oxazolidinones, streptogramins, glycopeptides and azoles

Goal of dosing regimen: optimize amount of drug

AUC/MIC major parameter correlating with efficacy

• Cyclophosphamide 150 and 100 mg/kg at 4 and 1 day before infection

• Thigh infection produced by injection of 0.1 ml of 107 CFU/ml 2 hrs before treatment

• Lung infection produced by 45 min aerosol of 109 CFU/ml 14 hrs before treatment

• 107-8 CFU/g in thigh or lung at start of therapy

Neutropenic Murine Thigh and Lung Infection Models

• Use neutropenic murine thigh-and lung-infection models

• Evaluate 20-30 different dosing regimens (5 different total doses given at 4-6 different dosing intervals)

• Measure efficacy from change in Log10 CFU per thigh or

lung at the end of 24 hours of therapy

• Correlate efficacy with various pharmacodynamic parameters (Time above MIC, peak/MIC, 24-Hr AUC/MIC)

Correlation of Pharmacodynamic Parameters with Efficacy

Correlation of PK/PD Parameters with Efficacy of Temafloxacin against Streptococcus pneumoniae

in Thighs of Neutropenic Mice

24-Hr AUC/MIC

10 100 1000

Log

10 C

FU/T

high

at 2

4 H

rs

0

2

4

6

8

10

Peak/MIC

1 10 100 1000

Time Above MIC

0 25 50 75 100

Craig in Antimicrobial Pharmacodynamics in Theory and Clinical Practice, p 1, 2002

Correlation of PK/PD Parameters and Efficacyfor Ceftazidime against Klebsiella pneumoniae

in a Murine Pneumonia Model

24-Hr AUC/MIC

10 100 1000

Log

10 C

FU

/Thi

gh a

t 24

Hrs

2

3

4

5

6

7

8

9

10

Peak/MIC

1 10 100 1000

Time Above MIC

0 25 50 75 100

Craig in Antimicrobial Pharmacodynamics in Theory and Clinical Practice, p 1, 2002

PK/PD Parameters

Does the magnitude of the parameter vary markedly with:

1. different animal species

2. the dosing regimen?

3. different drugs within the same class?

4. different organisms ?

5. different sites of infection (e.g. blood, lung, peritoneum, soft tissue)?

6. the presence of neutrophils?

Mathematical Analysis of Dose-Response Data from Animal Models

after 24 Hours of Therapy

Nonlinear regression andHill equation to estimate Emax (difference from untreated control), P50 (dose giving 50% ofEmax) and slope (N) of the dose-responserelationship

Dose (mg/kg/6 hrs)10 30 100 300

Lo

g1

0 C

FU

pe

r T

hig

h a

t 2

4 H

rs

5

6

7

8

9

Static Dose

1 Log K ill

P50

Emax

CFU=(Emax) DoseN

DoseN + P50N

PK/PD Parameters: -Lactams

Time above MIC is the important parameter determining efficacy of the -Lactams

T>MIC required for static dose vary from 25-40% of dosing interval for penicillins and cephalosporins to 10-25% for carbapenems

Free drug levels of penicillins and cephalosporins need to exceed the MIC for 40-50% of the dosing interval to produce maximum survival

Drug q1-2 h q3-4h q6-8h q12-24h Cephalosporins 53 ± 20 43 ± 15 42 ± 14 35 ± 11

Penicillins 29 ± 10 31 ± 14 34 ± 16 31 ± 12

Carbapenem 20 ± 4 26 ± 10 23 ± 6 20 ± 4

Craig et al 33rd ICAAC, 1993 (Abstract 86)

Time Above MIC Required for a Static Effect After 24-hrs of Therapy with Three

ß-Lactam Classes

Time Above MIC (Percent of Dosing Interval)

Drug Enterobacteriaceae S. pneumoniae S.aureus

Ceftazidime 36 (27-42) 39 (35-42) 20,25

Cefepime 35 (29-40) 37 (33-39) 21,24

Cefotaxime 38 (36-40) 38 (36-40) 22,25

Ceftriaxone (T) 62 (56-69) 64 (59-68) 46,69

Ceftriaxone (F) 38 (34-42) 39 (37-41) 24,26

Time Above MIC Required for a Bacteriostatic Effect with Four Cephalosporins

Time Above MIC (% of Dosing Interval)

Relationship Between MIC and T>MIC for the Static Dose for Cefpodoxime and Cefditoren

with Various Strains of S. pneumoniae

MIC (mg/L)

0.016 0.06 0.25 1 4 16

Tim

e A

bo

ve M

IC (

%)

20

30

40

50

60

70

Cefpodoxime (T)Cefditoren (T)Cefditoren (F)

Urban et al. 19th ICC 1995(Abstract 2229); Craig, Andes 40th ICAAC (Abstract 2248);

Literature Review for T>MIC for Beta-Lactams Versus Mortality in Animal Models

• At least 48 hrs of treatment

• Mortality 80-100% in untreated controls

• Pharmacokinetics provided to calculate magnitude of PK/PD parameter

• Mortality recorded within 24 hrs after last dose of drug

• Data from 3 animal species and 4 sites of infection

0 20 40 60 80 100M

orta

lity

(%)

0

20

40

60

80

100

Cephalosporins Penicillins

Time Above MIC (% of Interval)

Craig CID 26:1, 1998; Nicolau et al. AAC 44:1291, 2000

Relationship Between T>MIC and Bacterial Eradication with Beta-Lactams in Otitis Media

(Circles) and Maxillary Sinusitis (Squares) Bacteriologic cure for different

ß-lactams with S. pneumoniae and H. influenzae from double tap studies in acute otitis media and acute maxillary sinusitis

Time above MIC calculated from serum levels and MICs for different organisms

Craig & Andes, Pediatr Infect Dis J 15:255, 1996; Dagan et al JAC 47:129, 2001;Dagan et al Pediatr Infect Dis J 20:829, 2001

Time Above MIC (percent)

0 20 40 60 80 100

Bac

teria

l Era

dica

tion

(per

cent

)0

20

40

60

80

100

PSSP

PISP-PRSP

H. influenza

PK/PD Paramters with Fluoroquinolones

• 24-hr AUC/MIC 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

24-Hr AUC/MIC with Total and Free Drug for the Static Dose of Different Fluoroquinolones

with S. pneumoniae ATCC 10813

0

40

80

120

160

Gati Sita Moxi Gemi Garen Levo Cipro

24-H

r A

UC

/MIC

Total

Free

Andes & Craig 40th and 41st ICAAC, 2000 and 2001

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

Relationship Between 24 Hr AUC/MIC and Mortality in Animals for

Fluoroquinolones against Gram-Negative Bacilli

Andes & Craig, Int J of Antimicrob Agents 19:259, 2002

24-Hr AUC/MIC2.5 10 25 100 250 1000

Mor

talit

y (%

)

0

20

40

60

80

100

Comparison of Relationships Between 24-Hr AUC/MIC and Efficacy against Pneumococci

for Fluoroquinolones in Animals and Patients

• 58 patients enrolled in a comparative trial of levofloxacin vs gatifloxacin

• Free-drug 24-hr AUC/MIC <33.7, the probability of a microbiologic cure was 64%

• Free-drug 24-hr AUC/MIC >33.7, the probability of a microbiologic cure was 100%

24-Hr AUC/MIC1 2.5 10 25 100 250 1000

Mor

talit

y (%

)

0

20

40

60

80

100

Animals - Literature Review Patients with CAP and AECB

Andes & Craig, Int J of Antimicrob Agents 19:259, 2002 Ambrose et al AAC 45:2793, 2001

Impact of Dosing Interval on Static Dose for Amikacin against K. Pneumoniae and E. coli

in Mice with Normal and Impaired Renal Function

Dosing Interval (Hours)

3 6 12 24Sta

tic D

ose

(mg/

kg/2

4 hr

s)

1

10

100

1000

K. pneumoniaeE. coliNormal T1/2=17 min K. pneumoniae E. coliRenal Impaired T1/2=104 min

Reddington and Craig, JAC 1995

Impact of Dosing Frequency on Static Dose

for Macrolides and Azalides with Streptococcus pneumoniae ATCC 10813

Dosing Interval (Hours)

3 6 12 24

Sta

tic D

ose

(m

g/k

g/2

4 H

rs)

1

2.5

5

10

25

50

100

250

Erythromycin Clarithromycin Azithromycin

Drug

24-Hr AUC/MIC with Total and Free Drug for the Static Dose of Different Macrolides, Ketolides

and Clindamycin with S. pneumoniae ATCC 10813

1

10

100

1000

Erythro Roxi Clari Azi Clinda ABT-773

HMR-6004

24-H

r A

UC

/MIC

Total

Free

Craig et al. 42nd ICAAC, 2002

Animal Models for Susceptibility Breakpoint Determinations

• Simulate human pharmacokinetics in animals (induce renal impairment with uranyl nitrate)

• Infect groups of animals with organisms with varying MICs

• Treat the animals for at least 24 hours with dosage regimen used to treat human infections

• Find the MIC value that separates bacterial killing from bacterial growth

Effect of Amoxicillin (7 mg/kg) on 17 Strains of

S. pneumoniae in Thighs of Neutropenic Mice

-4

-3

-2

-1

0

1

2

3

MICs (mg/L)

5.6

4.04.0

4.0

2.02.0

1.00.5

0.50.5

0.2

5

0.2

5

0.0

6

0.0

3

0.0

6

0.0

6

0.0

16

Ch

an

ge

in L

og

CF

U

Ove

r 2

4 H

ou

rs

PK/PD ParametersDoes the magnitude of the parameter vary markedly with:

1. different animal species NO

2. the dosing regimen? NO

3. different drugs within the same class? NO providing free drug levels are used

4. different organisms ? Some (S. aureus-ß-lactams)

5. different sites of infection (e.g. blood, lung, peritoneum, soft tissue)? NO

6. the presence of neutrophils? YES, some drugs more than others