Phenytoin (Epsolin) Dosing for a 25 kg Child
For a 25 kg child, administer a loading dose of 500 mg (20 mg/kg) of intravenous phenytoin infused over 10–20 minutes, not exceeding 1 mg/kg/min (25 mg/min for this child), followed by maintenance dosing of 5 mg/kg/day divided into two doses starting 12–24 hours after the loading dose. 1
Loading Dose Administration
- The standard loading dose is 20 mg/kg intravenously, which equals 500 mg for a 25 kg child 1
- Infuse over 10–20 minutes with a maximum infusion rate of 1 mg/kg/min (not exceeding 25 mg/min for this child) 1
- If fosphenytoin is available, it is preferred because it has a lower risk of adverse cardiac effects and can be infused more rapidly (up to 2 mg PE/kg/min or 50 mg PE/min for this child) 1, 2
Critical Administration Requirements
- Dilute phenytoin only in normal saline to avoid precipitation; it is incompatible with glucose-containing solutions 1
- Monitor heart rate continuously during infusion and reduce the infusion rate if heart rate decreases by 10 beats per minute 1
- Be prepared to provide respiratory support, as there is an increased incidence of apnea when combined with other sedative agents 1
- Monitor oxygen saturation throughout the infusion 1
Maintenance Dosing
- Start maintenance therapy at 5 mg/kg/day (125 mg/day for a 25 kg child), typically divided into two doses 3
- Begin maintenance dosing 12–24 hours after the loading dose 1
- Adjust subsequent doses based on clinical response and serum phenytoin levels 3
Monitoring Parameters
- Obtain serum phenytoin level 1–3 hours after completion of the loading dose to confirm therapeutic range (10–20 mcg/mL) 4, 5
- Therapeutic levels should be achieved within 30 minutes of completing the infusion in most patients 1
- Continue cardiac monitoring for hypotension and arrhythmias, especially with rapid infusion 1, 2
Important Safety Considerations
Cardiovascular Risks
- Phenytoin may cause hypotension and arrhythmias, particularly with rapid infusion 1
- Continuous heart rate monitoring is mandatory; slow or stop the infusion if bradycardia develops 1, 2
Repeat Dosing if Needed
- A second loading dose of 10 mg/kg (250 mg) may be given 15 minutes after the initial dose if seizures persist, with a maximum total loading dose of 30 mg/kg (750 mg for this child) 1
- Reassess clinical response and serum levels before administering additional doses 4
Weight-Based Dosing Accuracy
- Use actual measured weight whenever possible rather than estimated weight, as estimation errors can result in doses ranging from 78% to 138% of the intended dose 4
- In this cohort, 20% of children achieved supra-therapeutic levels (>20 mcg/mL) with the 20 mg/kg loading dose, with three experiencing adverse effects consistent with phenytoin toxicity 4
Common Pitfalls to Avoid
- Never mix phenytoin with dextrose-containing solutions, as this causes immediate precipitation 1, 2
- Do not infuse faster than 1 mg/kg/min (25 mg/min for a 25 kg child) to minimize cardiovascular complications 1
- Avoid using phenytoin in neonates when possible, as they have increased risk of toxicity due to decreased protein binding; phenobarbital is preferred in this age group 1
- Do not assume therapeutic levels will persist beyond 24 hours without maintenance dosing, as phenytoin has complex pharmacokinetics in children 4, 6