How to read drug levels (therapeutic monitoring)
Other platforms explain it with text and video. In VMS you practice it on the patient.
Some drugs have a narrow gap between a helpful dose and a toxic one. Reading their blood levels correctly keeps the patient safe.
Step by step
Know why the level was sent
Check whether it is routine monitoring, a suspected overdose or a check after a dose change. [1]
Check the timing
A trough is drawn just before the next dose and a peak shortly after it. A level drawn at the wrong time cannot be read against the target. [2]
Confirm steady state
Most drugs reach a stable level after about 4 to 5 half-lives. An earlier level may be misleadingly low. [2]
Compare with the target range
Use the range for that drug and that use. Always read the number together with the patient's symptoms. [3]
Look for factors that shift levels
Kidney or liver disease, interacting drugs, low albumin and missed doses can all change a level. [2]
Act on a toxic level
Hold the next dose, check the patient for signs of toxicity and tell the prescriber. Some drugs, like digoxin, have an antidote. [2]
Document and recheck
Write the time of the last dose and of the sample. Plan when to check the next level. [1]
Common errors
- Reading a level drawn at the wrong time.
- Treating the number and ignoring the patient.
- Missing an interacting drug that raised the level.
Typical adult target ranges; use your lab's ranges [2]
| Drug | Usual target | Common signs of toxicity |
|---|---|---|
| Digoxin | 0.5 to 0.9 ng/mL (heart failure) | Nausea, vision changes, arrhythmias |
| Lithium | 0.6 to 1.2 mEq/L | Tremor, diarrhea, confusion |
| Phenytoin (total) | 10 to 20 mcg/mL | Jerky eye movements, unsteady walk |
| Valproic acid | 50 to 100 mcg/mL | Drowsiness, high ammonia |
| Vancomycin | AUC 400 to 600 mg h/L | Kidney injury |
Practice it in VMS
In VMS you do this on the patient, not on paper: every step goes on the checklist with a score, and in Teach mode Blocky tells you what comes next.
VMS cases that train this skill
Sources
- AAMC Core Entrustable Professional Activities (Core EPAs)
- Open RN, Nursing Pharmacology 2e (CC BY 4.0)
- NCCPA PANCE Content Blueprint
Facts and steps follow AAMC Core Entrustable Professional Activities (Core EPAs); NCCPA PANCE Content Blueprint. VMS is not affiliated with these organizations. Updated: 2026-10-11.