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Clobazam

Drug Monitoring

CLBFrisiumOnfi

Review status

Currently under review

Pending specialist review and validation.

What it shows

Clobazam is an antiseizure medicine in the benzodiazepine family. This blood test measures the amount of clobazam, and often its main active metabolite, circulating in your bloodstream to help guide safe and effective dosing. It shows how your body absorbs, metabolizes, and clears the medication over time.

Testing is usually timed at a steady point in your treatment, often just before your next dose, so your care team can compare results reliably. Because levels can be influenced by liver function, age, genetics, and other medicines, measuring them helps personalize your therapy.

Why it matters

Getting the concentration into the right zone supports seizure control while limiting side effects such as sleepiness, dizziness, slowed thinking, poor coordination, and breathing problems. Levels that are too low may be associated with breakthrough seizures, while levels that are too high can increase adverse effects and reduce quality of life.

Your clinician may order this test when you start clobazam, after dose changes, if seizures or side effects change, when other interacting drugs are added or stopped, during pregnancy, and in children or older adults. It can also help check adherence, assess potential drug interactions, and inform adjustments in the setting of liver disease or genetic differences in drug metabolism.

Understanding your results

Your report will list measured concentrations for clobazam and sometimes the active metabolite. If values are below the target interval for you, possible reasons include missed or delayed doses, drug interactions that increase clearance, blood sampling too soon after a dose, or individual differences in metabolism. Your clinician may adjust the dose or dosing schedule, address adherence and timing, consider interactions, and repeat testing.

If values are higher than expected, causes can include reduced liver function, drug interactions that slow metabolism, or taking doses closer together than intended. A pattern where the metabolite is relatively higher than the parent drug can occur with certain interactions or genetic profiles and may relate to excessive sedation. Results are interpreted alongside your symptoms and seizure control, and any changes are made carefully with follow-up plans.

Reference ranges

210 umol/L
All sexes
0 days – 150 years

Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.

Factors that could impact Clobazam

  • Timing of the blood draw

    For consistent interpretation, the sample is usually collected just before your next dose at steady state. Samples taken at other times can read higher or lower and may not reflect your usual baseline.

  • Drug interactions

    Medicines that affect liver enzymes can change clobazam and metabolite levels. Inhibitors such as stiripentol, fluconazole, fluvoxamine, or omeprazole can raise levels, while inducers like carbamazepine, phenytoin, phenobarbital, or rifampin can lower them. Cannabidiol can also increase metabolite levels.

  • Liver function and genetics

    Clobazam is processed in the liver, and reduced liver function can increase exposure. Genetic differences, especially in CYP2C19, can slow or speed metabolism, altering the balance between clobazam and its active metabolite.

  • Age, pregnancy, and physiological changes

    Children, older adults, and people who are pregnant can have different drug handling, which may shift expected levels. Changes in body weight and overall health can also influence results.

  • Adherence and formulation

    Missed doses, dosing at irregular times, or switching between tablets and liquid without careful measurement can change results. Always tell the lab and your clinician when you took your last dose and which formulation you use.

  • Alcohol and other sedatives

    Alcohol, opioids, sleep medicines, and other benzodiazepines can increase sedation and breathing risks even if clobazam levels are within the expected range. Your clinician may adjust therapy to reduce combined effects.

2026

References

  1. McGill University Health Centre. (2006, August 25). Clobazam (Task CD 699123). Laboratory reference ranges.
  2. McGill University Health Centre. (2006, August 25). Clobazam (Task CD 793138). Laboratory reference ranges.
  3. Patsalos, P. N., Berry, D. J., Bourgeois, B. F. D., Cloyd, J. C., Glauser, T. A., Johannessen, S. I., Leppik, I. E., Tomson, T., & Perucca, E. (2018). Therapeutic drug monitoring of antiepileptic drugs: A 2018 update. Therapeutic Drug Monitoring, 40(5), 526–548.
  4. U.S. Food and Drug Administration. (2021). Onfi (clobazam) prescribing information.