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Review of tobramycin levels in paediatric cystic fibrosis patients at Birmingham Children's Hospital
  1. L E Paskin1,2,
  2. M C Nock2,
  3. M Desai1,
  4. C A Langley2
  1. 1Birmingham Children's Hospital NHS Trust, Birmingham, UK
  2. 2School of Pharmacy, Aston University, Birmingham, UK

Abstract

Objective Cystic fibrosis (CF) is a common recessive disorder with the lungs one of the primary organs affected. Many patients experience chronic pulmonary infection by Pseudomonas aeruginosa. Tobramycin, an aminoglycoside is currently used in combination with additional antibiotics to manage the growth of P aeruginosa. As tobramycin has a narrow therapeutic index it requires extensive monitoring to ensure appropriate use. The aim of this study was to review the current practice in administration and monitoring of once daily intravenous tobramycin in paediatric CF patients receiving multiple courses at Birmingham Children's Hospital (BCH).

Method A retrospective audit of 49 once daily tobramycin courses in 15 patients (5 male; 10 female) was undertaken during 2010. All patients were under the care of BCH and had received two or more courses of intravenous antibiotics including tobramycin. Data were collected from patients' hospital records recording; patient height, weight, dosage and time of administration, drug plasma levels, urea and electrolyte levels.

Results The median number of courses for the population reviewed per patient was three. Once daily tobramycin was administered at a mean dose of 9.94 mg/kg (n=49, range 8.8–11.0) which conforms to current BCH guidelines. At least one trough level was observed for every course (mean=1.33; n=49). Trough levels greater than 1 mg/l were seen in 17% (n=11/65) of samples, 27% (n=3/11) of these were >2 mg/l. In reporting of trough levels 63% (n=41/65) had no reference range quoted and 37% (n=24/65) had incorrect ranges. Tobramycin was administered after 3 pm in 97% (n=39/40) of courses administered and 23% (n=9/40) were after 9 pm. Only 39% (n=19/49) of courses had renal function and electrolytes recorded on the admission which differs from practice elsewhere in the UK. However, almost all patients (98%; n=48/49) had renal function and electrolytes monitored in the last year which is an accepted standard. It was also observed no patients underwent routine monitoring for ototoxicity.

Conclusion The monitoring of tobramycin in CF patients varies within the UK. Current practice at BCH with regard to the dosing of once daily tobramycin and the timing of the first trough level are consistent with available guidelines. However an improvement in presentation of trough results would be desirable to ensure no risk of misinterpretation. The monitoring of renal function annually is in line with the UK CF Trust's recommendations but does differ from other CF centres and guidelines where creatinine levels should be taken at least once within a 14 day course.1 Current audiology arrangements need to be reviewed to ensure at risk patients receive appropriate monitoring. In this study a significant proportion of courses were administered in the evening which may result in an increased risk of toxic effects, due to a potential decrease in glomerular filtration rate. Further research is currently been undertaken in this area.

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