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 Tobramycin Policy
• 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 CGH and GRH Chemical Pathology – please send requests using green Chemistry request forms to avoid delays in sample receipt and analysis
• For requests out of hours please contact the on call biomedical scientist in Chemical Pathology to inform them that a sample is being sent

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
• For patients on bd or tds tobramycin regimes paired pre and 1 hour post-dose levels should be taken – the first levels should be taken when the patient has been on tobramycin for 48 hours. Repeat levels should be taken every 5-7 days if the first levels were satisfactory and the renal function is satisfactory and stable. If the first levels were unsatisfactory and the regime was altered, the levels should be repeated 48 hours after the regime change
• 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

• 5.0 mL of blood taken into a narrow gold top gel tube

For Small Children and Neonates

• A minimum of 1 mL of whole blood taken into a plain or heparinised tube

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 always less than 24 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 (Antibiotic guide Home Page)

 

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

24 hour post-dose (pre-dose) ≤ 1 mg/L

See policy: Tobramycin (intravenous) Daily dosing for Paediatric Patients A0264

 

• Target levels for bd or tds dosing in adults:

Pre-dose <2 mg/L

Post-dose (1 hour) 5-10 mg/L

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