Therapeutic drug monitoring
How to request and read a drug level step by step (timing, steady state, sample tube, total versus free, renal and hepatic function), worked examples for lithium, vancomycin and carbamazepine, laboratory monitoring for adverse reactions, and when a result should change the dose.
Tier 1Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- A drug level answers one of four questions: is the dose adequate, is the patient toxic, is the patient taking it, or has something changed (renal function, an interaction, pregnancy)?
- No level can be read without the time of the last dose and knowing whether the patient is at steady state.
- Most errors are pre-analytical: wrong time, wrong tube, sample from the infusion line.
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Sources
- Therapeutic Guidelines: Antibiotic (vancomycin and aminoglycoside dosing and monitoring)AU/NZTherapeutic Guidelines Limited, 2025
- Legg A, Devchand M, Gwee A, Sandaradura I, Lai T. Safe and effective use of vancomycin. Aust Prescr 2025;48:54-9AU/NZAustralian Prescriber, 2025
- RCPA Manual: therapeutic drug monitoring test entries (lithium, digoxin, antiepileptics, immunosuppressants)AU/NZRoyal College of Pathologists of Australasia, online, accessed 2026
- Australian Medicines HandbookAU/NZAustralian Medicines Handbook Pty Ltd, 2026
- Rybak MJ et al. Therapeutic monitoring of vancomycin for serious MRSA infections: a revised consensus guideline. Am J Health Syst Pharm 2020;77:835-64ASHP, IDSA, PIDS and SIDP, 2020
- Nolen WA et al. The ISBD task force report on the optimal serum lithium level. Bipolar Disord 2019;21:394-409International Society for Bipolar Disorders, 2019
- Decker BS et al. Extracorporeal treatment for lithium poisoning: systematic review and recommendations from the EXTRIP Workgroup. Clin J Am Soc Nephrol 2015;10:875-87Clinical Journal of the American Society of Nephrology, 2015
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Turnstile bot check on sign-in and signed-out feedback