Macrolide Limitations H. influenzae — SCE Infectious Diseases MCQ

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ModerateAntimicrobial StewardshipMacrolide Limitations H. influenzaeSCE Infectious Diseases

A 65-year-old man with COPD develops acute exacerbation with purulent sputum. He has had 2 courses of Amoxicillin in the past 3 months. Sputum culture grows Haemophilus influenzae with a beta-lactamase. Current guidelines would suggest escalation. His GP prescribes a macrolide instead of Co-amoxiclav. Why is this suboptimal?

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Correct answer: A — Macrolide resistance in H. influenzae is approximately 20–25% in the UK — and H. influenzae is intrinsically less susceptible to macrolides than to beta-lactams even when 'susceptible'

The suboptimal choice is E. In an acute infective exacerbation of COPD, purulent sputum plus repeated recent antibiotic exposure increases the likelihood of resistant bacterial infection. NICE recommends considering previous antibiotic use, previous sputum culture/susceptibility results, and the risk of antimicrobial resistance; patients with repeated courses of antibiotics or resistant/current sputum culture are at higher risk of treatment failure, for whom co-amoxiclav is an appropriate oral escalation option guided by susceptibilities. Here, Haemophilus influenzae has produced a beta-lactamase, so plain amoxicillin is compromised, whereas co-amoxiclav adds clavulanate to inhibit beta-lactamase. A macrolide is not the best targeted escalation: UK COPD isolate data report macrolide resistance of about 20–25% for H. influenzae, and EUCAST notes that clinical evidence for macrolide efficacy in H. influenzae respiratory infection is problematic/conflicting; H. influenzae has baseline reduced susceptibility to macrolides even when reported as susceptible. Therefore, switching to a macrolide ignores both the resistance risk and the microbiology; co-amoxiclav has a clear advantage in this scenario.

Reference: NICE NG114, Chronic obstructive pulmonary disease (acute exacerbation): antimicrobial prescribing, 2018 (current online recommendations): https://www.nice.org.uk/guidance/ng114/chapter/Recommendations; EUCAST Clinical Breakpoint Tables v16.0, 2026, Haemophilus influenzae macrolide notes: https://www.eucast.org/clinical_breakpoints; Ampicillin resistance in Haemophilus influenzae from COPD patients in the UK, International Journal of COPD 2017;12:1507-1518, doi:10.2147/COPD.S135338