Phenytoin and fosphenytoin loading dose
Loading dose to reach a target level, using obesity-adjusted weight and any current level.
Inputs
2 of 5SexUsed by the equation
Actual (total) body weight
mg/L
0 if no level yet.
mg/L
Patient values are shared with every calculator.
When to use
- Loading or reloading phenytoin or fosphenytoin.
Pearls and pitfalls
- Status epilepticus guideline dose is 20 mg PE/kg (max 1500 mg PE).
- IV phenytoin no faster than 50 mg/min (adults); fosphenytoin up to 150 mg PE/min, with cardiac monitoring.
- Fosphenytoin is dosed in phenytoin equivalents (PE).
Why use
Accounts for the level already on board and for obesity, where actual weight overestimates Vd.
Load (mg) = Vd × weight × (target − current); Vd = 0.7 L/kg; obese weight = IBW + 1.33 × (TBW − IBW)