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Table 3 Dosing and monitoring of commonly used antiepileptic drugs [8, 11, 15, 16]

From: Antiepileptic drugs in critically ill patients

Antiepileptic drug Dose Therapeutic drug level to treat epilepsy (μg/mL) Monitoring TDM clinical pearls
Phenytoin Load: 15–20 mg/kg
Maintenance:
4–6 mg/kg/day
10–20 1 h postload or
~ 7–10 days after initiation of maintenance dose (may check earlier within 2–3 days in seizing patients to ensure their metabolism is not significantly different from average patient population)
At total concentrations > 20 μg/mL, nystagmus may occur.
In concentrations > 30 μg/mL, ataxia, slurred speech, and incoordination can be observed.
If total concentrations are above 40 μg/mL, coma is possible.
At concentrations > 50–60 μg/m drug induced seizures may occur
Valproic acid Load: 20–40 mg/kg
Maintenance:
10–15 mg/kg/day
50–100 (levels as high as 175 are used in RSE) 1 h postload or
2–4 days after initiation of maintenance dose
At total concentrations > 75 μg/mL lethargy and ataxia may occur.
In concentrations > 100 μg/mL tremor is observed. Coma may occur if total serum concentrations are above 175 μg/mL.
Thrombocytopenia is a dose-related side effect that can be limited by reducing the dose
Phenobarbital Load: 20 mg/kg
Maintenance: 1.5–2 mg/kg/day
(dose adjustment may be required in liver impairment due to reduced clearance)
15–40 (higher levels may be utilized in RSE) 1 h postload or
4–7 days after initiation of maintenance dose
CNS depression is a dose-related side effect. In concentrations > 60 μg/mL respiratory depression may occur
Pentobarbital Load: 5–15 mg/kg
Maintenance: 0.5–5 mg/kg/h
1–5 (rarely used to assess clinical efficacy or toxicity) May be used after discontinuation to monitor the residual effects of the drug Drug levels have not been correlated with electroencephalography
CNS depression, respiratory depression, and hemodynamic instability are dose-related side effects
  1. CNS central nervous system, RSE Refractory Status Epilepticus, TDM therapeutic drug monitoring