Clinical use
Therapeutic drug monitoring of Posaconazole. Requesters have found these assays to be of value in patients with gastrointestinal dysfunction receiving therapy with proton pump inhibitors to confirm optimal oral absorption.
Background
Therapeutic drug monitoring (TDM) 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. 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.
Reference ranges
Routine in majority of patients. Measure 3-8 days after starting therapy
Prophylaxis: Pre: 0.7-3.75 mg/L
Therapy: Pre: 1.0-3.75 mg/L
All pre-dose levels to be kept below 3.75 mg/L
Patient preparation
Obtain samples: Oral posaconazole pre-dose and after 5 days
We recommend a pre dose sample taken immediately before administration.Approx. 1-2mL of separated serum. It is best to use a plain clotted blood tube for collection.
- Serum sample
- Do not use serum separator tubes with a gel plug for azole drugs. This is because the gel may bind the analyte, which may result in an artificially lower result being obtained, interpreted, and reported.
Transport time must be <4 weeks. Samples should be kept at 4°c if there is a delay in sending. Please contact the laboratory if in doubt, as sample integrity may be affected. Samples must be sealed and packed to conform to current regulations. Leaking samples may not be processed.
Please supply the following on request:
Clinical Summary
Dosage, frequency, and timing of samples
Specimen requirements
Approx. 1-2mL of separated serum. It is best to use a plain clotted blood tube for collection.
- Serum sample
- Do not use serum separator tubes with a gel plug for azole drugs. This is because the gel may bind the analyte, which may result in an artificially lower result being obtained, interpreted, and reported.
Transport time must be <4 weeks. Samples should be kept at 4°c if there is a delay in sending. Please contact the laboratory if in doubt, as sample integrity may be affected. Samples must be sealed and packed to conform to current regulations. Leaking samples may not be processed.
Please supply the following on request:
- Dosage, frequency, and timing of samples
- Clinical Summary
Minimum volume
Supply 1 to 2ml serum taken at the appropriate times – and labelled accordingly
Turnaround time
<2 day from arrival at the reference laboratory.
Analysing laboratory
UKHSA Mycology Reference Laboratory, National Infection Services, UKHSA South West Laboratory, Science, Quarter, Southmead Hospital, Bristol, BS10 5NB
Additional information
Not normally required during our core working hours (Mon – Fri 09:00 – 17:15). Please contact the laboratory to discuss the possibility of this assay being performed on Saturdays, Sundays, and Bank Holidays.
If there is concern regarding TDM please discuss it with Microbiology or the Antimicrobial pharmacy team.
More details for this test can be found at North Bristol Antimicrobial Reference Laboratory.