Clinical use
Therapeutic monitoring of itraconazole levels during treatment.
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
The trough level should be maintained above 0.5 mg/L. Less than 0.5mg/L is a low concentration. Limited published data suggests that outcomes are better when the voriconazole levels are above 2 mg/L.
There may be toxicity issues at higher concentrations (greater than 4 mg/L). Liver function tests should be monitored during prolonged courses.
Patient preparation
When to obtain samples: Oral or IV itraconazole pre-dose and after 7 days
Specimen requirements
- Red top plain clotted blood.
- For oral or IV itraconazole: specimens should be obtained pre-dose after 7 days.
Minimum volume
1 – 2 ml of serum
Limitations & restrictions
Yellow top serum separator tubes are not suitable for this test. Azole levels may be affected by the gel plug in a serum separation tube (SST), therefore please send samples in a plain clotted blood tube with no additives.
Turnaround time
<1 day from receipt 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
Please visit the guidance page for the UKHSA Mycology Reference Laboratory for further information.