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Tobramycin

Chemical Pathology

Notes

  • All patients receiving tobramycin must have levels monitored, primarily to avoid renal toxicity
  • Renal function should also be regularly monitored
  • For most patients requiring a tobramycin course a once daily dosing regime can be used
  • Instructions for prescribing tobramycin and monitoring levels can be found in the adult Tobramycin Policy. See also local guidelines / action cards in Paediatrics including action card A2167: Once Daily Intravenous Tobramycin (in paediatric patients with Cystic Fibrosis)
  • Tobramycin levels can be taken at any time of day but the collection time should be convenient for the patient and for the testing laboratory – sampling and testing between 12 midnight and 6 am should be avoided –see "when to test"
  • Most tobramycin levels are a planned non-urgent investigation
  • Tobramycin levels are performed both at GRH Chemical Pathology – please routinely request Tobramycin levels electronically in Sunrise - send requests and collected specimens directly to Chemical Pathology (not Microbiology) to avoid delays in sample receipt and analysis

When to test

  • For a once daily dosing regime samples should be taken 12 to 18 hours after the dose. For ease of interpretation it is recommended to take the levels at exactly 12 or 18 hours after the dose. If the levels are within the recommended range with normal renal function then the levels should be repeated twice weekly
  • If the renal function is abnormal or changing the levels should be monitored more frequently (every 2 days)

Sample requirements

Samples must NOT be taken via lines

For Adults

5ml gold tube

For Children

3.5ml rust top tube

For neonates

Minicollect lithium heparin tube

Storage/transport

Do not store. Send at ambient temperature to the laboratory as soon as possible.

Clinical Information required

  • Tobramycin dose and frequency
  • Time of last dose
  • Date and time sample collected

Turnaround time

  • The assays are run throughout the day and night. The in-lab turnaround time is less than 6 hours.
  • Results are made available on the computer as soon as they are technically approved. Additional comments may be added later by the Consultant Microbiologist when results are clinically approved.
  • The test can be ordered as an urgent investigation

Result interpretation

If there is any doubt regarding interpretation, or a dose change needs to be discussed, then contact the Consultant Microbiologist

Normal levels

  • Target levels for once daily dosing in adults:

12 hours post-dose <2 mg/L

18 hours post-dose <1 mg/L

To interpret levels from between these times see graph (nomogram) in the tobramycin policy.

Dose adjustments should be made as per policy (Once Daily Tobramycin: Administration and Monitoring Protocol)

  • Target levels for once daily dosing in children with cystic fibrosis:

24 hour post-dose (pre-dose) ≤ 1 mg/L

See action card A2167: Once Daily Intravenous Tobramycin (in paediatric patients with Cystic Fibrosis) A2167

If you need advice please contact the duty consultant microbiologist or ward pharmacist.

Page last updated: 19/06/2025

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