From the Research
For a 7kg patient, the recommended loading dose of Phenytoin is 20 mg/kg, which equals 140 mg total, and this should be diluted in 100 ml of Normal Saline and administered at a maximum rate of 1 mg/kg/minute, which is 7 mg/minute for this patient. This translates to a drip rate of approximately 5 ml/minute (or 300 ml/hour) if using the 140 mg dose. The infusion should be given through a large vein using an in-line filter, with continuous cardiac monitoring due to the risk of hypotension and cardiac arrhythmias, as noted in studies such as 1 and 2. Phenytoin should never be infused faster than the recommended rate as this can cause cardiovascular collapse. After the loading dose, a maintenance dose of 5-8 mg/kg/day divided into two doses would be appropriate. Phenytoin is highly protein-bound and has nonlinear pharmacokinetics, so therapeutic drug monitoring is essential to ensure effective and safe treatment, especially in pediatric patients where drug metabolism can vary significantly, as discussed in 3 and 4. The choice of 20 mg/kg as the loading dose is supported by a study 5 which found that this dose is easier to calculate correctly and therefore safer than the 18 mg/kg dose. Key points to consider in the administration of Phenytoin include:
- Dose calculation: 20 mg/kg for a loading dose
- Administration rate: not to exceed 1 mg/kg/minute
- Monitoring: continuous cardiac monitoring and therapeutic drug monitoring
- Potential risks: hypotension, cardiac arrhythmias, and cardiovascular collapse if infused too quickly.