Adapting Bloodculture Systems to Monitor Antimicrobial Efficacy

Principle Investigator: Irene Zaghi, M.D.

Supervisors:

• Russell E. Lewis, Pharm.D., University of Padua
• Monica Cricca, M.D., Ph.D., University of Bologna
• Vittorio Sambri, M.D., Ph.D., Univeristy of Bologna

January 20, 2023

Antibiotic dosing is an uncertain science

Image: Irene Zaghi, M.D.

Antibiotic dosing is an uncertain science

(Theuretzbacher 2012; Roberts et al. 2014)

Antibiotic dosing is an uncertain science

(Theuretzbacher 2012; Roberts et al. 2014)

How can dosing uncertainty be managed?

(Roberts et al. 2014)

Dosing uncertainty at the dawn of penicillin resistance

(Schlichter and Mac Lean 1947)

Dosing uncertainty at the dawn of penicillin resistance

“It was felt that there was a need of some definite basis for determining adequate therapy for each specific infectious organism involved…”

“Current methods in general use all depend on indirect comparisons (MICs, measurement of penicillin blood levels). In patients with more resistant organisms, it has not been demonstrated that this is the proper approach…”

“…It occurred to us that a more satisfactory method of outlining adequate therapy in resistant organisms might be based on the action of the patient’s own serum during penicillin administration.”

(Schlichter and Mac Lean 1947)

Serum bactericidal test (SBT)

(CLSI 1999; Zaghi et al. 2020)

SBTs correlate with antibiotic PK/PD

(Zaghi et al. 2020)

Potential clinical utility of SBTs

Individual patient-level diagnostic meta-analysis (1947-2020)

Prognostic performance similar or better than current susceptibility breakpoints

(Zaghi et al. 2020)

SBT advantages

• Only microbiological test that accounts for both antibiotic PK and PD
• Accounts for protein binding changes
• Can detect synergistic or antagonistic antibiotic interactions

Why were SBTs abandoned?

• Insufficient standardization despite published methods
  • CLSI M21-A, last updated 1999
• Poor inter-laboratory reproducibility
• Labour-intensive to perform
• Lack of perceived need after introduction of reliably bactericidal antibiotics in 1990s
  • 3rd generation cephalosporins, fluoroquinolones, carbapenems
• Delay in results reporting (48-72 hours with patients isolate)

“I read your SBT review and have a suggestion…”

Use continuously-monitored bloodculture systems Time-to-positivity (Tpos) to measure bactericidal activity

Concept: The assay will measure time taken for a standardized bacterial inoculum to “grow through” the antimicrobial activity in the patient’s serum under defined conditions.

• A short Tpos would indicate inadequate antimicrobial activity and should predict a worse outcome
• A long Tpos is evidence of adequate antimicrobial activity and should predict a good outcome

Blood culture Tpos measures bacterial inoculum and antimicrobial pharmacokinetics

A “critical” Tpos result could be reported in < 12 hours!

(Kaltsas, Want, and Cohen 2005; Jerwood, Hankins, and Cohen 2012)

Adapting Bloodculture Systems to Monitor Antimicrobial Efficacy

• Specific Aim# 1: Establish the quantitative relationship in vitro between Tpos and carbapenamase-producing Enterobacterales (CPE) and define antibiotic concentration-effect relationships
• Specific Aim#2: Pilot observational clinical study in 20 septic patients undergoing treatment for CPE to explore how early Tpos results with “indicator” isolates correlate with individual antibiotic PK/PD targets

Tpos correlates with inoculum

• K. pneumoniae
• E. coli
• A. baumanii
• P. aeruginosa

R² = 0.96-0.99

Tpos can discriminate between susceptible and resistant pathogens

KPC_B MIC 1.0 mg/L, KPC_NDM MIC > 256 mg/L; data fit by Loess

Pharmacodynamic relationship of Tpos against
K. pneumoniae ATCC 700603 (0.75 mg/L)

• Ceftazidime-avibactam
• 4:1 ratio
• Fixed 4 mg/L

	Estimate	Lower .95	Upper .95
0.1	23.87874	19.31716	28.44033
0.25	26.93812	24.06902	29.80723
0.5	30.38948	29.11007	31.66888
0.75	34.28302	31.38838	37.17767
0.9	38.67541	33.84814	43.50268
0.95	41.98020	33.98412	49.97627

	Estimate	Lower .95	Upper .95
0.1	8.099087	7.038485	9.159689
0.25	9.235833	8.728989	9.742676
0.5	10.532127	10.149119	10.915134
0.75	12.010361	10.856802	13.163921
0.9	13.696074	11.685276	15.706872
0.95	14.975851	12.415855	17.535846

Inoculum effects observed with PD relationship measured by Tpos

At a standardized inoculum, Tpos demonstrates a consistent relationship across different antibiotics and isolates with different MICs

Tpos for directed antimicrobial therapy “in vivo MIC”

Tpos performed using indicator isolates to screen for suboptimal PK/PD

Comparison of K. pneumoniae indicator isolates

Figure 1: Pharmacodynamic relationship of Tpos to ceftazidime/avibactam concentrations

Isolate PD coverage of ceftazidime-avibactam

Combination therapy

Synergy of ceftazidime-avibactam plus gentamicin versus KPC-producing K. pneumoniae

Combination therapy versus Klebsiella pneumoniaeo

Antibiotic combination	Strain (Ceftazidime-avibactam MIC mg/L)	Mean Tpos change (hr) from predicted null response surface (95% CI)
CZA + GENT	KP_A; KPC (2)	+5.68 (5.09-6.53)
CZA + GENT	KP_B; KPC (1)	+3.05 (2.16-4.03)
CZA + GENT	KP_Catania; KPC (16)	+3.23 (2.10-4.14)
CZA + COL	KP_B; KPC (1)	+2.31 (1.40-3.20)
CZA + TGC	KP_B ;KPC (1)	+1.66 (0.72-2.73)
CZA + ATM	KP_NDM;NDM-2 (> 64)	+10.33 (10.32-10.34)
CZA + ATM	KP_Catania; KPC (16)	+10.36 (10.31-10.35)
CZA + MER	KP_B; KPC (1)	+11.61 (11.05-11.95)
CZA + MER	KP_Catania; KPC (16)	+3.04 (2.15-4.03)

Impact of combination therapy on high-inoculum infections

synergistic activity improved but did not overcome effects of high-inoculum infection

Adapting Bloodculture Systems to Monitor Antimicrobial Efficacy

Specific Aim# 1: Establish the quantitative relationship in vitro between Tpos and carbapenamase-producing Enterobacterales (CPE) and define antibiotic concentration-effect relationships

Specific Aim#2: Pilot observational clinical study in 20 septic patients undergoing treatment for CPE to explore how early Tpos results with “indicator” isolates correlate with individual antibiotic PK/PD targets

Longer range goals

• Develop population PK/PD tools for interpreting and predicting Tpos with ceftazidime-avibactam and other core antibiotics
• Expand Tpos analysis for other difficult to treat Gram-negative pathogens (e.g., Acinetobacter baumanii, Pseudomonas aeruginosa) and Candida spp.
• Future multicentre collaborative trials (validation, testing)
• Pilot projects to develop Tpos as dosing tools in LMICs?

Acknowledgements

Supervisors:

• Prof. Russell Lewis, Department of Molecular Medicine, University Of Padua
• Prof. Monica Cricca, Department of Diagnostic and Experimental Medicine, University of Bologna
• Prof. Vittorio Sambri, Department of Diagnostic and Experimental Medicine, University of Bologna
• Faculty and staff at the Microbiology Unit, Greater Romagna Area Hub, Pievesistina, Cesena, Italy

Funding:

Direzione Generale Della Ricerca Dell’ Innovazione in Sanità 2021-Bando Dell Ricerca

European Society of Clinical Microbiology and Infectious Diseases (ESCMID) 2022 Research Grants Program

Antibiotic powder:

References

CLSI. 1999. Methodology for the Serum Bactericidal Test; Approved Guideline M21-A.

Jerwood, Susannah, Matthew Hankins, and Jon Cohen. 2012. “A Pilot Clinical Trial to Evaluate a Novel Time-to-Positivity Assay to Measure the Effectiveness of Antibiotic Therapy for Septic Patients in Intensive Care.” Journal of Critical Care 27 (3): 320.e1–5. https://doi.org/10.1016/j.jcrc.2011.06.009.

Kaltsas, P, S Want, and J Cohen. 2005. “Development of a Time-to-Positivity Assay as a Tool in the Antibiotic Management of Septic Patients.” Clinical Microbiology and Infection: The Official Publication of the European Society of Clinical Microbiology and Infectious Diseases 11 (2): 109–14. https://doi.org/10.1111/j.1469-0691.2004.01054.x.

Roberts, Jason A, Mohd H Abdul-Aziz, Jeffrey Lipman, Johan W Mouton, Alexander A Vinks, Timothy W Felton, William W Hope, et al. 2014. “Individualised Antibiotic Dosing for Patients Who Are Critically Ill: Challenges and Potential Solutions.” The Lancet Infectious Diseases 14 (6): 498–509. https://doi.org/10.1016/s1473-3099(14)70036-2.

Schlichter, J. G., and H. Mac Lean. 1947. “A Method of Determining the Effective Therapeutic Level in the Treatment of Subacute Bacterial Endocarditis with Penicillin; a Preliminary Report.” American Heart Journal 34 (2): 209–11. https://doi.org/10.1016/0002-8703(47)90289-5.

Theuretzbacher, Ursula. 2012. “Pharmacokinetic and Pharmacodynamic Issues for Antimicrobial Therapy in Patients with Cancer.” Clinical Infectious Diseases: An Official Publication of the Infectious Diseases Society of America 54 (12): 1785–92. https://doi.org/10.1093/cid/cis210.

Zaghi, I., P. Gaibani, C. Campoli, M. Bartoletti, M. Giannella, S. Ambretti, P. Viale, and R. E. Lewis. 2020. “Serum Bactericidal Titres for Monitoring Antimicrobial Therapy: Current Status and Potential Role in the Management of Multidrug-Resistant Gram-negative Infections.” Clinical Microbiology and Infection 26 (10): 1338–44. https://doi.org/10.1016/j.cmi.2020.04.036.