Antiseizure Medication Concentrations and Labeled Dosages
Do not infer efficacy, toxicity, dosage, or treatment changes from a concentration alone. Verify the exact formulation, indication, age, timing of blood sampling, last dose, and patient-specific clinical factors.
| Generic and referenced product | Reported blood concentration |
|---|---|
| Sodium valproateAmel sustained-release tablets, 100 mg and 200 mg (SR tablet type A) | 40–120μg/mL |
| PhenytoinHydantol oral tablets 25 mg and 100 mg | 10–20μg/mL |
| PhenobarbitalPhenobal oral preparations: powder, 10% granules, 30 mg tablets and 0.4% elixir | 10–25μg/mL |
These figures are not universal normal ranges, target levels or thresholds for dosage adjustment. Consult the product-specific indication and labeling below.
Products, indications and dosage references
Usual dose summaries describe only specific referenced Japanese oral products. They do not instruct initiation, cessation or dose adjustment.
Sodium valproate
- Referenced formulation
- Amel sustained-release tablets, 100 mg and 200 mg (SR tablet type A)
- Indication and reported concentration
- Specified epilepsy-related indications in the Japanese labeling. Concentration reported for the labeled epilepsy-related indications; NOT an age-specific therapeutic target.Another report in the package insert also suggests 50–150 μg/mL.
- Labeled usual dosage (reference only)
- Package-insert summary for these epilepsy indications: usual oral daily total 400–1,200 mg in 1–2 divided doses; adjust for age and symptoms.The selected dose section does not state an explicit age category and is NOT a pediatric-specific prescription.
- Important note
- Blood levels may change when switching from another valproate formulation (section 8.4).
- Source
- PMDA Japanese package insert (March 2026, revision 6; sections 4, 6, 8.4, 16.8.1)
Phenytoin
- Referenced formulation
- Hydantol oral tablets 25 mg and 100 mg
- Indication and reported concentration
- Adult tonic-clonic seizures (population for the concentration guidance). General concentration guidance for adult tonic-clonic seizures, not all seizure types or ages.Interpretation varies with seizure severity and patient factors.
- Labeled usual dosage (reference only)
- Package-insert adult usual oral daily total: 200–300 mg divided into 3 post-meal doses; adjust for symptoms and tolerance.The selected dose section is for adults; pediatric dosing elsewhere in the insert is not reproduced here.
- Important note
- Concentrations respond nonlinearly to dosage changes, with high individual variability (section 16.8.2).
- Source
- PMDA Japanese package insert (April 2026, revision 3; sections 4, 6, 7, 16.8.1, 16.8.2)
Phenobarbital
- Referenced formulation
- Phenobal oral preparations: powder, 10% granules, 30 mg tablets and 0.4% elixir
- Indication and reported concentration
- Epilepsy-related convulsive, autonomic and psychomotor seizures. Concentration range reported in the specified epilepsy indication sections.NOT an individual therapeutic target or a toxicity threshold.
- Labeled usual dosage (reference only)
- Package-insert adult usual oral daily total: 30–200 mg divided into 1–4 doses; adjust for age and symptoms.The selected dose section is for adults; no blanket pediatric dose is supplied here.
- Important note
- Abrupt reduction or withdrawal during epilepsy treatment risks status epilepticus (section 8.4).
- Source
- PMDA Japanese package insert (April 2026, revision 3; sections 4, 6, 8.4, 16.8.1)
Blood sampling, scope and approval status
Timing and pharmacokinetic interpretation
The selected sections 16.8.1 do not specify one uniform sampling time for interpreting all three drugs. Do not assume these are trough targets. Check sample timing, last dose, dose interval, interacting drugs and organ function.
Scope restrictions
Formulation substitution, pediatric care, pregnancy, low serum albumin, and concomitant therapies require individual professional review. No automatic dose calculation or therapeutic range recommendation is performed.
Review status
Source comparison date 2026-11-10. Independently summarized from the cited PMDA electronic package inserts. No original third-party image or OCR content is reproduced.