Clinical use
Therapeutic drug monitoring (TDM) of daptomycin may be of value in patients with complex infections and/or impaired renal function.
Background
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 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 Daptomycin TDM, pre and post dose levels should be sent. Take the post dose level 1 hour after IV infusion. This can be repeated at 6-8 days if initial results are within range.
When using Daptomycin it is also important to take a baseline plasma creatine phosphokinase (CK) measurement, and repeat this twice weekly while on treatment to monitor for signs of muscle toxicity.
Reference ranges
- For a 6-8mg/kg dose: Pre dose 5-25mg/L or Pre dose 10-25mg/L in severe sepsis or deep-seated infection
- Pre dose levels >24.3mg/L associated with increased risk of toxicity.
Patient preparation
Reference laboratory recommendation: pre dose sample and a post dose sample, taken 1 hour after the end of IV administration.
Specimen requirements
Sample request forms must state the following clinical information:
- Dosing schedule being used (dose and frequency of dosing interval)
- Time of last dose of antibiotic
- Time and date the level was taken
- Approx. 1-2mL of separated serum (the minimum acceptable is 100µL)
- Gold top serum separator
Minimum volume
100µL
Turnaround time
<3 days from receipt at the reference laboratory
Analysing laboratory
Antimicrobial Reference Laboratory, Level 2, Phase 1, Pathology Sciences Building, Southmead Hospital, Westbury-on-Trym, Bristol, BS10 5NB
Additional Information
Please visit the guidance page for the Antimicrobial Reference Laboratory for more information.