Necessity of tobramycin trough levels in once daily iv-treatment in
patients with cystic fibrosis
Abstract
Background: Once daily intravenous (iv) treatment with tobramycin for
Pseudomonas aeruginosa infection in patients with cystic fibrosis (CF)
is usually monitored by measuring tobramycin trough levels. Although the
necessity of these trough levels is recently questioned in CF patients
without renal impairment, no study has evaluated this so far. The aim of
this observational study was to evaluate the frequency of increased
tobramycin trough levels in 278 courses of iv tobramycin in CF children
and adolescents. Methods: Patient records of all consecutive once daily
iv tobramycin courses in 35 CF patients between 07/2009 and 07/2019 were
analyzed for tobramycin level, renal function, co-medication and
comorbidity. Results: Eight elevated tobramycin levels (2.9% of 278
courses) were recorded in four patients, two with normal renal function.
One of these did resolve without adjustment of tobramycin dosages
suggesting laboratory error. In the other patient elevated tobramycin
levels occurred after recently being started on lumacaftor/ivacaftor and
decreased after dosage adjustment. Six of the elevated levels occurred
in two patients with chronic renal failure. In 15 other patients with
reduced glomerular filtration rate (GFR) (36 courses) no case of an
elevated tobramycin trough level was detected. Cumulative tobramycin
dosages were neither a risk factor for elevated trough levels nor were
diabetes or nutritional status. Conclusion: In CF patients with normal
GFR (GFR >100 ml/min) and in absence of additional risk
factors (e.g. recently started CFTR modulator therapy) a monitoring of
the once daily iv treatment by tobramycin trough levels seems not to be
necessary.