Department

Microbiology Biochemistry

Preferred Sample Type

Suitable Specimen Types

Serum

1 -2 mL minimum

Specimen Transport

If unable to send immeadiately please refrigerate sample

Sample Processing in Laboratory

Usual

Sample Preparation

Centrifuge

Turnaround Time

2 days

Sample Stability

Separated samples may be stored for up to 7 days at 2 to 8°C

Tobramycin Antibiotic Assay

General Information

Antimicrobial drugs normally have a high therapeutic index with supratherapeutic doses given safely (e.g. penicillins, macrolides, sulphonamides). The situation is different for aminoglycosides, which may cause significant toxicity just above the concentration required for bactericidal activity.

Tobramycin is an aminoglycoside and is a broad-spectrum antibiotic which has to be given by injection. It is excreted by the kidneys and if levels are too high, can permanently damage the kidneys and hearing. Toxicity is principally related to a high pre-dose level, as it means that the drug is not being excreted as quickly as it should be and is therefore accumulating in the body.

Tobramycin is used almost exclusively in cystic fibrosis and bronchiectasis patients. Generally on a single daily dosing regimen.

Patient Preparation

See reference range for timing of sample collection.

Notes

Take first sample after the 2nd - 4th dose of drug (t.d.s / b.d.s) or 1st to 3rd dose (once daily)

Interval for re-assay is usually 3 days

From 1st April 2016, please use Chemistry and Immunology request forms.

Please complete request forms with time of dosing and sampling.

Amikacin, kanamycin A, and kanamycin B cross-react with the Tobramycin assay due to their structural similarity. The results of this assay cannot be used to accurately quantitate tobramycin serum or plasma levels in patients receiving any of these drugs in combination with tobramycin

Reference Range

Multiple Daily Dosing

Pre dose (trough) blood sample 15 mins before dose < 2mg/L

Post dose (peak) blood sample 1 hour after dose 5 - 10mg/L

N.B. Ranges and comments DO NOT apply to Renal patients

Once Daily Dosing

Pre dose (trough) < 1 mg/L

Please refer to Antibiotic guidelines on the HEFT website for further information (http://pharmacy/?page_id=922)

For diagnostic purposes, the test findings should always be assessed in conjunction with the patient’s medical history, clinical examinations, and other findings

Specifications

EQA Scheme?: Yes
EQA Status: NEQAS

Link to Further Information

http://www.heftpathology.com/Microbiology/micro-antibiotic-assay-protocol.html