Fosphenytoin Loading Dose Calculation
For a 68 kg male, administer 1020-1360 mg PE (phenytoin equivalents) of fosphenytoin as a loading dose, calculated using 15-20 mg PE/kg. 1
Dose Calculation
Standard loading dose range: 15-20 mg PE/kg 1
- Lower end (15 mg PE/kg): 15 × 68 kg = 1020 mg PE
- Upper end (20 mg PE/kg): 20 × 68 kg = 1360 mg PE
For status epilepticus specifically, use the full 15-20 mg PE/kg range 1
For non-emergent situations, a 10-20 mg PE/kg loading dose is acceptable, though the lower range (10-15 mg PE/kg) may be considered 1
Administration Rate
Maximum infusion rate: 100-150 mg PE/min in adults 1
Never exceed 150 mg PE/min due to risk of severe hypotension and cardiac arrhythmias 1
For this 68 kg patient receiving 1020-1360 mg PE, infusion time would be approximately 7-14 minutes at maximum rate 1
Critical Safety Requirements
Continuous cardiac monitoring is mandatory during and after administration 2, 3
Reduce infusion rate if heart rate decreases by 10 beats/min 2, 3
Monitor for bradycardia, arrhythmias, heart block, and hypotension 2
Preparation Guidelines
Dilute only in normal saline to a final concentration ≥5 mg PE/mL 2
Never use dextrose-containing solutions as this causes precipitation 2, 3
Ensure prescription specifies "mg PE" to prevent 10-fold dosing errors 2
Special Considerations
In obese patients, actual body weight should be used for dosing calculations, with at least 15 mg PE/kg recommended to achieve therapeutic concentrations 4
Therapeutic free phenytoin levels (1-2 mcg/mL) are typically achieved within 10 minutes of completing the infusion 5, 6
Most patients (83%) maintain therapeutic levels at 24 hours after appropriate loading 5