Safety of Extended Interval Tobramycin in Cystic Fibrosis Patients Less an 6 Years Old.

OBJECTIVES: The primary objective of this study was to assess the nephrotoxicity and ototoxicity risks of extended interval tobramycin in cystic fibrosis (CF) patients who are <6 years old. A secondary objective included analyzing pharmacokinetic parameters in this age group.

METHODS: A retrospective chart review was conducted of patients with CF who were <6 years old, admitted for an acute pulmonary exacerbation from January 1, 2003, to January 1, 2014, and treated with intravenous tobramycin.

RESULTS: The median baseline serum creatinine (SCr) was 0.26 mg/dL among the 31 patients included in the study. Of the 20 patients who experienced increases in SCr, the absolute median increase was 0.065 mg/dL (0.033-0.1 mg/dL). Abnormal audiograms seen in 4 patients are attributable to middle ear effusion present on exam. The median dose of tobramycin was 11.7 mg/kg (11.3-12 mg/kg), the elimination constant was 0.4 hr-1 (0.32-0.47 hr-1 ), half-life was 1.7 hr (1.5-2.1 hr), volume of distribution was 0.37 L/kg (0.31-0.47 L/kg), and median peaks and troughs fell within ranges of 20 to 30 mg/L (20.9-32.7 mg/L) and <0.01 mg/L, respectively.

CONCLUSIONS: Extended interval dosing tobramycin is safe in CF patients who are <6 years old. There was no drug-related ototoxicity, and some nephrotoxicity was observed. When dosed at 12 mg/kg, similar pharmacokinetics were seen among all age groups, and concentrations were within the desired range.