Results of antibiotic susceptibility testing do not influence clinical outcome in children with cystic fibrosis

Introduction: Patients with CF experience pulmonary exacerbations. These are often initially empirically treated with intravenous antibiotics, with antibiotic choice refined after susceptibility testing. Methods: We completed a 5-year retrospective review of children attending the Paediatric CF Unit, Nottingham. The respiratory sampling, antibiotic prescribing and susceptibility testing guidance were audited. Episodes were classified according to the concordance between the antibiotics prescribed and antibiotic susceptibility testing. Results: Of 52 patients who had previously isolated Pseudomonas aeruginosa, 103 antibiotic courses were commenced that coincided with an isolation of P. aeruginosa. P. aeruginosa was fully susceptible, partially susceptible or fully resistant on 33%, 44.7% or 16.5% of occasions respectively. The antibiotic prescriptions were never changed following antibiotic susceptibility testing. We found no association between change in FEV ₁ (p=0.54), change in BMI (p=0.12) or time to next exacerbation (p=0.66) and concordance between antibiotic susceptibility and the antibiotics administered. Conclusion: This study contributes to mounting evidence questioning the utility of routine antibiotic susceptibility testing.