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Tobramycin Pharmacokinetics in Pediatric People With Cystic Fibrosis on Maintenance Azithromycin

Chelsea Flora1, Samantha Engdahl2, Rebecca S Pettit2

  • 1Indiana University Health, Indianapolis, Indiana, USA.

Pediatric Pulmonology
|May 13, 2026
PubMed

Insights

Maintenance azithromycin (mtAZM) does not impact tobramycin (TOB) pharmacokinetics in pediatric cystic fibrosis patients. This suggests similar TOB dosing and monitoring can be used, regardless of mtAZM use.

Area of Science:

  • Pharmacology
  • Cystic Fibrosis Research
  • Infectious Disease Management

Background:

  • Pseudomonas aeruginosa colonization is common in cystic fibrosis patients.
  • Concomitant use of tobramycin (TOB) and azithromycin (AZM) in cystic fibrosis pulmonary exacerbations (PEx) has been linked to poorer clinical outcomes.
  • Potential drug interactions necessitate investigation into pharmacokinetic parameters.

Purpose of the Study:

  • To compare the intravenous tobramycin (IV TOB) elimination rate constant (Ke) in pediatric cystic fibrosis patients receiving maintenance azithromycin (mtAZM) versus those not on mtAZM.
  • To evaluate the impact of mtAZM on TOB pharmacokinetics during PEx treatment.

Main Methods:

  • Retrospective cohort study of pediatric cystic fibrosis patients receiving IV TOB for PEx.
  • Comparison of TOB elimination rate constant (Ke) between patients on mtAZM and those not on mtAZM.
  • Analysis of other pharmacokinetic parameters, dosing, and clinical outcomes.

Main Results:

  • No significant difference in mean TOB Ke between the mtAZM group (0.39 h⁻¹) and the no mtAZM group (0.42 h⁻¹).
  • Similarities observed in other pharmacokinetic parameters, median TOB daily dose, duration of TOB use, and re-admission rates.
  • No significant difference in the percentage of females between groups (60% vs 38%).

Conclusions:

  • Maintenance azithromycin (mtAZM) does not significantly alter the elimination rate constant (Ke) or other pharmacokinetic parameters of intravenous tobramycin (IV TOB).
  • Findings suggest that current TOB dosing and monitoring strategies are appropriate for pediatric cystic fibrosis patients, irrespective of their mtAZM use.
  • This research addresses concerns about potential drug interactions, supporting current treatment protocols.
Abstract

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