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

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