Microbiology

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Microbiology

• Jeff Alder, Ph.D.
• Vice President, Drug Discovery and
  EvaluationCubist Pharmaceuticals

2
Analysis of MIC Shifts

• Unprecedented microbiology database
• 1,215 S. aureus isolates were tested for MICs
• First study to examine serial isolate
  susceptibility in SAB patients
• MIC shifts to ? 2 noted
• Daptomycin- and vancomycin-treated patients
• Different susceptibility criteria
• Scientific investigations with these isolates
• Bacteria, drug, patient

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Wild-type Distribution of S. aureus Isolates
Includes Daptomycin MICs of 2 µg/mL
No. of Isolates MIC90 (µg/mL) Range (µg/mL) MIC of 2 µg/mLn ()
Regional Surveys Regional Surveys
1998-2003 5,248 0.25 - 1 ? 0.12 - 2 8 (0.15)
Global Surveillance Studies Global Surveillance Studies Global Surveillance Studies
1999-2001 2,787 0.25 - 0.5 ? 0.12 - 2 1 (0.04)
2002 2,623 0.5 ? 0.12 - 2 2 (0.08)
2003 4,362 0.5 ? 0.12 - 2 1 (0.02)
2004 5,260 0.5 ? 0.12 - 2 2 (0.04)
2005 6,374 0.5 ? 0.12 - 2 3 (0.05)
Total 26,654 NA ? 0.12 - 2 17 (0.06)

• MICs of 2 µg/mL were observed prior to approval
  (Sept 03)

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Daptomycin-treated Patients with Post-baseline
Daptomycin MICs of 2 and 4

• MIC 4 µg/mL (N 1)
• 1 failure (cRIE large septic pulmonary emboli,
  tunnel infection)
• MIC 2 µg/mL (N 6)
• 1 success (cBAC vertebral osteomyelitis,
  debrided x2)
• 3 failures (cBAC IV port infection, septic
  arthritis, retroperitoneal abscess)
• 2 failures (LIE no valve replacement surgery)
• Failed patients did not or could not receive
  adjunctive therapy (e.g., surgery, drainage)

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Vancomycin-treated Patients with Post-baseline
Vancomycin MICs of ? 2

• 2 patients by Central Lab testing
• 1 success (cRIE)
• 1 failure (cBAC septic thrombophlebitis)
• 5 additional patients by Local Lab testing
• 1 failure (LIE no valve replacement surgery)
• 3 failures (cBAC sternal osteomyelitis,
  abscesses, ulcers)
• 1 failure (uBAC abdominal wound with mesh)
• Failed patients did not or could not receive
  adjunctive therapy (e.g., surgery, drainage)

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Serial Passage ExperimentsMagnitude of MIC
Shifts
140
120
100
80
Fold Change (Strain MIC/Parent MIC)-1
60
40
20
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Day
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Genes Involved in S. aureus Susceptibility
Genetic Change Isolate Source Isolate Source Isolate Source Isolate Source Isolate Source
Genetic Change Wild-type (Non-exposed) Wild-type (Non-exposed) SAB/SAIEStudy Clinical Use Serial Passage
Genetic Change (MIC ? 1) (MIC 2) (MIC 2-4) (MIC 2-8) (MIC 2-16)
mprF - ? ? ? ?
yycG - - - ? ?
rpoB - - - - ?
rpoC - - - - ?

• mprF mutations Part of the wild-type
  distribution
• yycG mutations First unique change seen in MIC
  ? 4 clinical isolates, but not seen in wild-type
  isolates

Genetic loci identified using whole genome
comparisons between CA-MRSA MW2 and lab-derived
MW2 strains with increasing daptomycin MICs
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Genes Involved in S. aureus Susceptibility
Genetic Change Isolate Source Isolate Source Isolate Source Isolate Source Isolate Source
Genetic Change Wild-type (Non-exposed) Wild-type (Non-exposed) SAB/SAIE Study Clinical Use Serial Passage
Genetic Change (MIC ? 1) (MIC 2) (MIC 2-4) (MIC 2-8) (MIC 2-16)
mprF - ? ? ? ?
yycG - - - ? ?
rpoB - - - - ?
rpoC - - - - ?

• mprF mutations Part of the wild-type
  distribution
• yycG mutations First unique change seen in MIC
  ? 4 clinical isolates, but not seen in wild-type
  isolates

Genetic loci identified using whole genome
comparisons between CA-MRSA MW2 and lab-derived
MW2 strains with increasing daptomycin MICs
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Pharmacodynamics of S. aureus in MiceLab-derived
Isolates of CA-MRSA MW2
2000
1766
1800
1600
1400
1200
Total AUC for 3 log10 Reduction(µghr/mL)
1031
1000
800
Median AUC 543 µghr/mLwith the human 6 mg/kg
dose
600
453
275
400
250
200
0
2
4
8
16
1
10
100
MIC Value (µg/mL)

• MICs ? 2 respond to similar drug exposure (AUC)
• MICs ? 4 require increasing levels of drug
  exposure

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Efficacy in Mice Against Baseline and
Post-baseline Isolates from the SAB/SAIE Study
Baseline
Post-baseline
1500
1250
1000
Total Plasma AUC for 3 log10 Reduction(µghr/mL)
750
500
250
0
152
212
105
037
183
136
172
Patient Number (Daptomycin-treated)
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Daptomycin Penetration into Simulated Endocardial
Vegetations
T 72h 2 doses
T 72h No treatment

• Daptomycin penetrates into rat fibrin clots
  exerts bactericidal activity

Mortin et al. ASM 2003 Tsuji and Rybak. AAC
2005 Caron et al. AAC 1992.
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Daptomycin Penetration into Simulated Endocardial
Vegetations
T 72h 2 doses
T 72h No treatment

• Daptomycin penetrates into rat fibrin clots
  exerts bactericidal activity
• Daptomycin achieved efficacy at simulated 6 mg/kg
  dose

Mortin et al. ASM 2003 Tsuji and Rybak. AAC
2005 Caron et al. AAC 1992.
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Daptomycin Penetration into Simulated Endocardial
Vegetations
T 72h 2 doses
T 72h No treatment

• Daptomycin penetrates into rat fibrin clots
  exerts bactericidal activity
• Daptomycin achieved efficacy at simulated 6 mg/kg
  dose
• 14C-daptomycin achieved homogenous penetration
  into rabbit vegetations

Mortin et al. ASM 2003 Tsuji and Rybak. AAC
2005 Caron et al. AAC 1992.
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Global Surveillance Data (MRSA)
70
MIC
? 0.12
60
0.25
0.5
1
50
2
40
Incidence
30
20
10
0
2000-2001
2002
2003
2004
2005
Study Year
Jones et al. Annual Surveillance Reports.
2002-2005.
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Microbiology Summary

• Additional investigations due to failures at MIC
  ? 2
• Bacteria, drug, patient
• No decisive bacterial or daptomycin factors
• No trends in surveillance
• Difficult to select for large MIC increases
• Incremental genetic changes
• Modeling shows adequate drug exposure and
  penetration
• Patient-specific factors likely play a role
• Complicated infections and outcomes
• Adjunctive care important
• Similar observations with vancomycin