Preferred Sample Type
Suitable Specimen Types
- Serum
Specimen Transport
If unable to send sample immediately please refrigerateSample Processing in Laboratory
UsualSample Preparation
CentrifugeTurnaround Time
2 daysSample Stability
Separated samples may be stored for up to 7 days at 2 to 8°CGentamicin 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.
Gentamicin is an aminoglycoside and is a broad-spectrum antibiotic which has to be given by injection due to the very poor oral bioavailability of the drug (F <0.05). 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.
Single daily dosing of gentamicin is used routinely in paediatrics (SCBU, NNU), haematology/oncology, ITU and areas such as orthopaedics and renal medicine. TDM results in single daily dosing should be interpreted using the Urban & Craig nomogram.
Multiple dosing of gentamicin is used, especially in endocarditis patients. Patients with endocarditis have Pre dose levels taken only. In other multiple dosing regimens both pre and post dose levels are required.
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.
The aminoglycoside sisomicin cross-reacts with the Gentamicin assay due to their structural similarity. Therefore, the results of this assay cannot be used to accurately quantitate gentamicin serum or plasma levels in patients receiving sisomicin in combination with gentamicin
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
In endocarditis pre dose <1mg/L and post dose 3 - 5mg/L
N.B. Ranges and comments DO NOT apply to Renal patients
Once Daily Dosing
Post-dose only taken between 6 and 14 hours after dose. Times of dosing and sampling must MUST be given on request form.
Refer to Urban & Craig nomogram to interpet
Please refer to Antibiotic guidelines on the HEFT website for further information (http://pharmacy/?page_id=922)
Specifications
- EQA Scheme?: Yes
- EQA Status: NEQAS