Therapeutic drug monitoring (TDM) of colistin. This assay may be of value in patients with renal failure and/or in cases of suspected nephrotoxicity.
TDM is the measurement of 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.
TDM aims to optimise individual dosage regimens, enabling the assessment of safety and efficacy of certain drugs, in combination 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.
If undertaking colistin TDM, levels should be sent on day 2-3 of treatment (if patient received a loading dose), and re-assessed at 5-7 days of treatment.
Pre dose: 2 – 4 mg/L
Recommendation from the reference laboratory: pre dose samples only will be accepted, taken up to an hour before dosing. Post dose samples will not be processed due to interpretation of the result potentially being misleading.
- Approx. 1-2mL of separated serum (the minimum acceptable is 100µL)
- Gold top serum separator
<3 days from receipt at the reference laboratory
Antimicrobial Reference Laboratory, Level 2, Phase 1, Pathology Sciences Building, Southmead Hospital, Westbury-on-Trym, Bristol, BS10 5NB
Please visit the guidance page for the Antimicrobial Reference Laboratory for more information.