Clinical use
Therapeutic drug monitoring. When patients are being treated with antibiotics such as this, it is important that levels are monitored to ensure that they are not so high that they are toxic or so low that they are ineffectual. This test may be of value in all patients treated for >48 hours and particularly in patients with cystic fibrosis who are receiving tobramycin once a day.
Background
Therapeutic drug monitoring is the measurement of specific drug concentrations in the blood at timed intervals, in order to maintain a relatively constant concentration of the medication in the circulation. Monitored drugs tend to have a narrow “therapeutic index” – the difference between the toxic and therapeutic doses of medications. For some drugs, maintaining this steady concentration in the blood cannot be achieved by simply giving a standard dose of medication to everyone. Each person will absorb, metabolise, utilise, and eliminate drugs at different rates based upon their age, general state of health, genetic makeup, and the influence of other medications that they are taking. These factors may change over time and vary from day to day or with various disease states.
Therapeutic drug monitoring (TDM) aims to optimise individual dosage regimens, enabling the assessment of safety and efficacy of certain drugs. Current TDM approaches include measuring drug serum concentration together with appropriate medical interpretation.
Candidate drugs for TDM possess one or more of the following: narrow therapeutic range, high pharmacokinetic (PK) variability and a clear relationship between serum concentration and therapeutic response. TDM is also helpful for the drug optimisation in patients with renal, hepatic or gastrointestinal insufficiency.
Reference ranges
Not readily provided by the reference laboratory.
Patient preparation
None required
Specimen requirements
- Adult: Serum separator tube, gold top
- Paediatric: clotted blood
Minimum volume
- Adult: 5ml
- Paediatric: 1ml
Turnaround time
<1 day from receipt at the reference laboratory
Analysing laboratory
Department of Microbiology, Freeman Hospital, Freeman Road, High Heaton, Newcastle Upon Tyne, Tyne and Wear, NE7 7DN
Additional information
More details for this test can be found at Newcastle Laboratories website.