Date of Award

1-1-2016

Document Type

Open Access Thesis

Degree Name

Master of Public Health (MPH)

Department

School of Public Health

First Advisor

Melinda Pettigrew

Abstract

Introduction

Chronic Obstructive Pulmonary Disease (COPD) is the third leading cause of death in the United States. Significant clinical disease in COPD patients has been tied to non-typeable Haemophilus influenzae (NTHI) infection. However, reasons why some NTHI strains persist despite antimicrobial therapy remain unknown.

Objective

The primary objective was to characterize the pharmacodynamics of azithromycin against a persistent pair of NTHI isolates.

Methods

A persistent pair of NTHI isolates (5P28H1 and 5P54H1) cultured from the sputum of an adult with COPD and determined to be the same strain by multilocus sequence typing was carried for 819 days. The Minimum Inhibitory Concentrations (MIC) were determined according to Clinical and Laboratory Standards Institute guidelines for 5P28H1 (MICazithromycin=2.0) and 5P54H1 (MICazithromycin=16.0). Time-kill experiments were performed using an array of azithromycin concentrations and samples were collected over 48h. The log reduction and integrated log ratio area over 48h were calculated and fit to a Hill-type model. A hollow-fiber infection model (HFIM) simulating azithromycin concentrations and pharmacokinetics in human serum and alveolar macrophages was performed over 240h for 5P28H1.

Results

Azithromycin displayed differential killing activity against 5P28H1 and 5P54H1. For 5P28H1, azithromycin concentrations >0.5 mg/L achieved complete killing by 48h. In contrast, complete bacterial killing was observed by 48h for concentrations >4 mg/L in 5P54H1. Overall, azithromycin demonstrated dose-dependent bactericidal activity against both isolates. Pharmacodynamic analysis revealed a right shift in the comparative dose response curves. Model fits were excellent (R2>0.99). Azithromycin serum concentrations simulated in HFIM did not appreciably reduce 5P28H1 viability by 240h, whereas simulated alveolar macrophage concentrations achieved complete killing by 26hrs.

Conclusion

Bactericidal activity was achieved for 5P28H1 at lower concentrations compared to 5P54H1, which demonstrated an attenuated killing profile. The differential pharmacodynamics of azithromycin suggests that antimicrobial pressure plays a role in counter selection of resistance for NTHI.

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