Background Antibiotics have altered pharmacokinetics (PK) in persons with cystic fibrosis (PwCF) during treatment for an acute pulmonary exacerbation (APE). The Cystic Fibrosis Foundation Pulmonary Guidelines–Treatment of Pulmonary Exacerbations do not provide specific recommendations for treatment of methicillin‐resistant Staphylococcus aureus (MRSA) lung infections. However, the American Thoracic Society Guidelines recommend vancomycin as the first‐line therapy. Only one study has previously described a single dose of intravenous (IV) vancomycin PK in adult PwCF. Our study aimed to describe intermittent IV vancomycin PK at steady‐state in adult PwCF. Methods Adult PwCF who were admitted to University of Utah Hospital between May 11, 2014 and August 31, 2020, and received intermittent IV vancomycin for the treatment of an APE were included in this study. The primary outcome was to describe the drug volume of distribution (Vd), drug clearance, elimination half‐life, and total daily dose of vancomycin. Secondary outcomes were rates of acute kidney injury (AKI), liver injury, and infusion‐related reactions. Results Thirteen patients were included. The mean Vd was 0.54 L/kg on Day 3 and 0.53L/kg on Day 7. CLvanco was 5.11L/h on Day 3 and 4.69 L/h on Day 7. Zero patients experienced an AKI, two patients experienced liver injury, and no patients experienced infusion‐related reactions. Conclusions Our results demonstrate that in PwCF intermittent IV vancomycin steady‐state PK are similar to previously reported single‐dose IV vancomycin. Additionally, CLvanco minimally changes from Day 3 to Day 7, although this study was not powered to detect a difference.

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