Disclaimer to the Online Edition
This Manual has been designed for use in the NICU at London Health Sciences Centre (LHSC), London, Ontario, Canada, and represents clinical practice at this institution. The information contained within the Manual may not be applicable to other centres. If users of this Manual are not familiar with a drug, it is recommended that the official monograph be consulted before it is prescribed and administered. Any user of this information is advised that the contributors, Editor and LHSC are not responsible for any errors or omissions, and / or any consequences arising from the use of the information in this Manual.
phenytoin
Indication
- Treatment of neonatal seizures which are refractory to maximal doses of PHENobarbital alone
Dosage Guidelines
- Loading Dose: 15-20 mg/kg/dose IV
- Maintenance dose: 2-4 mg/kg/dose IV/ORAL q12 hours (start 12 hours after loading dose)
Administration
- A 0.22 MICRON IN-LINE FILTER IS REQUIRED DUE TO THE POTENTIAL OF DRUG PRECIPITATION
- IV intermittent slow infusion. Usual maximum recommended rate is 0.5-1 mg/kg/min
- Phenytoin must be diluted to 5 mg/mL prior to administration
- Example Calculation on how to dilute a loading dose
Patient weight = 1500 g Loading dose = 20 mg/kg x 1.5 kg = 30 mg
30 mg divided by 50 mg/mL (phenytoin concentration) = 0.6 mL
To dilute this dose from a 50 mg/mL concentration to a 5 mg/mL, multiply the volume of the undiluted dose by 10 to determine the final volume of the 5 mg/mL syringe
0.6 mL x 10 = 6 mL final volume. Add 0.6 mL of phenytoin to 5.4 mL normal saline and administer entire 6 mL - Example Calculation on how to dilute a maintenance dose
Patient weight = 1500 g Maintenance dose = 3 mg/kg x 1.5 kg = 4.5 mg
4.5 mg divided by 50 mg/mL (phenytoin concentration) = 0.09 mL
To dilute this dose from a 50 mg/mL concentration to a 5 mg/mL, multiply the volume of the undiluted dose by 10 to determine the final volume of the 5 mg/mL syringe
0.09 mL x 10 = 0.9 mL final volume. Add 0.09 mL of phenytoin to 0.81 mL normal saline and administer entire 0.9 mL - Diluted solution must be used within 1 hour of preparation.
- Not compatible with dextrose solutions. Flush IV with normal saline before and after administration.
- Use peripheral IV if possible. Avoid using PICC line to reduce the risk of phenytoin crystallization and line occlusion
- ORAL
Adverse Effects
- Following IV administration: hypotension, bradycardia, ventricular fibrillation, vasodilation, venous irritation, pain, thrombophlebitis, skin rash.
- GI side effects: vomiting, constipation
- May be seen with chronic use: hepatotoxicity, gingival hyperplasia, hyperglycemia and osteoporosis
Comments
- Monitor IV site closely. To avoid local tissue injury, use a 5 mg/mL solution of phenytoin, flush the IV catheter with 0.9% NaCl before and after phenytoin administration and avoid small hand, wrist or foot veins.
- Monitor for hypotension and arrythmias during IV administration
- Oral route has slow and variable absorption
- Maintain serum phenytoin concentrations between 40-80 micromol/L. Draw level at least 2 hours after loading dose or 0 to 2 hours prior to the maintenance dose of Day 3 of maintenance.
- Peak effect: 30 minutes (IV), 4 to 7 hours (oral)
- Half-life 15 to 105 hours
Supplied As
- 50 mg/mL, 2 mL ampoule for IV use
- 25 mg/mL oral suspension
References
LexiComp Sick Kids, LexiComp Pediatric and Neonatal, Neofax