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Treatment responses to Azithromycin and Ciprofloxacin in uncomplicated Salmonella Typhi infection: A comparison of Clinical and Microbiological Data from a Controlled Human Infection Model

Jin, Celina, Gibani, Malick M, Pennington, Shaun. H ORCID:, Liu, Xinxue, Ardrey, Alison, Aljayyoussi, Ghaith, Moore, Maria, Angus, Brian, Parry, Christopher, Biagini, Giancarlo ORCID:, Feasey, Nicholas ORCID: and Pollard, Andrew J (2019) 'Treatment responses to Azithromycin and Ciprofloxacin in uncomplicated Salmonella Typhi infection: A comparison of Clinical and Microbiological Data from a Controlled Human Infection Model'. PLoS Neglected Tropical Diseases, Vol 13, Issue 12, e0007955.

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Background: The treatment of enteric fever is complicated by the emergence of antimicrobial resistant Salmonella Typhi. Azithromycin is commonly used for first-line treatment of uncomplicated enteric fever, but the response to treatment may be sub-optimal in some patient groups when compared with fluoroquinolones.

Methods: We performed an analysis of responses to treatment with azithromycin (500mg once-daily, 14 days) or ciprofloxacin (500mg twice-daily, 14 days) in healthy UK volunteers (18-60 years) enrolled into two Salmonella controlled human infection studies. Study A was a single-centre, open-label, randomised trial. Participants were randomised 1:1 to receive open-label oral ciprofloxacin or azithromycin, stratified by vaccine group (Vi-polysaccharide, Vi-conjugate or control Men-ACWY vaccine). Study B was an observational challenge/re-challenge study, where participants were randomised to challenge with Salmonella Typhi or Salmonella Paratyphi A. Outcome measures included fever clearance time, blood-culture clearance time and a composite measure of prolonged treatment response (persistent fever ≥38.0°C for ≥72 hours, persistently positive S. Typhi blood cultures for ≥72 hours, or change in antibiotic treatment). Both trials are registered with (NCT02324751 and NCT02192008).

Findings: In 81 participants diagnosed with S. Typhi in two studies, treatment with azithromycin was associated with prolonged bacteraemia (median 90.8 hours [95% CI: 65.9-93.8] vs. 20.1 hours [95% CI: 7.8-24.3], p<0.001) and prolonged fever clearance times <37.5oC (hazard ratio 2.4 [95%CI: 1.2-5.0]; p=0.02). Results were consistent when studies were analysed independently and in a sub-group of participants with no history of vaccination or previous challenge. A prolonged treatment response was observed significantly more frequently in the azithromycin group (28/52 [54.9%]) compared with the ciprofloxacin group (1/29 [3.5%]; p<0.001). In participants treated with azithromycin, observed systemic plasma concentrations of azithromycin did not exceed the minimum inhibitory concentration (MIC), whilst predicted intracellular concentrations did exceed the MIC. In participants treated with ciprofloxacin, the observed systemic plasma concentrations and predicted intracellular concentrations of ciprofloxacin exceeded the MIC.

Interpretation: Azithromycin at a dose of 500mg daily is an effective treatment for fully sensitive strains of S. Typhi but is associated with delayed treatment response and prolonged bacteraemia when compared with ciprofloxacin within the context of a human challenge model. Whilst the cellular accumulation of azithromycin is predicted to be sufficient to treat intracellular S. Typhi, systemic exposure may be sub-optimal for the elimination of extracellular circulating S. Typhi. In an era of increasing antimicrobial resistance, further studies are required to define appropriate azithromycin dosing regimens for enteric fever and to assess novel treatment strategies, including combination therapies.

Funding: The Bill & Melinda Gates Foundation; Medical Research Council UK (MRC)

Item Type: Article
Subjects: QV Pharmacology > Anti-Bacterial Agents. Tissue Extracts > QV 350 Anti-bacterial agents (General or not elsewhere classified)
QW Microbiology and Immunology > Bacteria > QW 138 Enterobacteriaceae
QW Microbiology and Immunology > QW 4 General works. Classify here works on microbiology as a whole.
QW Microbiology and Immunology > QW 45 Microbial drug resistance. General or not elsewhere classified.
WC Communicable Diseases > Infection. Bacterial Infections > Enteric Infections > WC 270 Typhoid fever
Faculty: Department: Biological Sciences > Department of Tropical Disease Biology
Clinical Sciences & International Health > Clinical Sciences Department
Digital Object Identifer (DOI):
Depositing User: Cathy Waldron
Date Deposited: 02 Jan 2020 11:37
Last Modified: 09 Jan 2020 16:33


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