What is the dose and drip rate of Phenytoin (antiepileptic medication) in normal saline (NS) for a 7kg boy with convulsions?

From the Guidelines

For a 7kg boy with convulsions, the recommended loading dose of Phenytoin is 20 mg/kg, which equals 140 mg, and should be administered intravenously at a maximum rate of 1 mg/kg/minute (7 mg/minute for this child) to avoid cardiovascular side effects, as stated in the most recent and highest quality study 1. The dose and drip rate of Phenytoin in normal saline (NS) for this patient can be calculated as follows:

• Loading dose: 20 mg/kg x 7 kg = 140 mg
• Maximum infusion rate: 1 mg/kg/minute x 7 kg = 7 mg/minute
• Dilution: 140 mg in 28 mL of NS (5 mg/mL) is appropriate
• Infusion time: 20 minutes
• Drip rate: approximately 1.4 mL/minute or 84 mL/hour It is essential to monitor the patient's cardiac function and IV site during administration, as Phenytoin can cause cardiovascular side effects and tissue damage, as noted in 1 and 1. The use of Phenytoin in this context is supported by its mechanism of action, which involves blocking sodium channels in neuronal membranes, stabilizing them and preventing the repetitive firing of action potentials that characterize seizures, as described in 1. In terms of potential alternatives, valproate may be considered for refractory convulsive status epilepticus if benzodiazepines fail, as an alternative to phenytoin or fosphenytoin, according to 1. However, the recommended treatment for this patient is Phenytoin, given its established efficacy and safety profile in this context, as stated in 1.

From the FDA Drug Label

The drug should be injected slowly intravenously at a rate not exceeding 1 to 3 mg/kg/min or 50 mg per minute, whichever is slower. A loading dose of 15 to 20 mg/kg of Phenytoin Sodium Injection intravenously will usually produce serum concentrations of phenytoin within the generally accepted serum total concentrations between 10 and 20 mcg/mL

For a 7kg boy, the dose would be:

• Loading dose: 15 to 20 mg/kg, so 15 to 20 mg/kg x 7 kg = 105 to 140 mg The drip rate should be:
• 1 to 3 mg/kg/min, so for a 7kg boy, the drip rate would be 1 to 3 mg/kg/min x 7 kg = 7 to 21 mg/min Alternatively, the drip rate should not exceed 50 mg per minute, whichever is slower. 2 2

From the Research

Dose of Phenytoin

• The dose of Phenytoin for a 7kg boy with convulsions is 18 mg/kg, as stated in the study 3.
• Another study 4 also mentions a loading dose of 18 mg/kg for children with severe malaria and status epilepticus.
• However, a study 5 suggests that a dose of 20 mg/kg may be easier to calculate and safer than 18 mg/kg.

Drip Rate of Phenytoin

• The study 3 mentions that the initial delivery rate was 40 mg/min, but it was reduced to 20 mg/min in some cases to relieve discomfort at the IV site.
• Another study 4 mentions that fosphenytoin, a prodrug of phenytoin, was administered at a rate of 50 mg/min phenytoin sodium equivalents.
• It is essential to note that the drip rate may need to be adjusted based on the individual patient's response and tolerance to the medication, as mentioned in the study 6.

Administration of Phenytoin

• Phenytoin should be administered in a solution of 50 mL normal saline, as stated in the study 3.
• The medication should be infused using a constant infusion pump, and the patient's cardiac rhythm, vital signs, and IV site should be closely monitored, as mentioned in the study 3.
• The study 4 also mentions that phenytoin can be administered intramuscularly, but this may not be the preferred route for a 7kg boy with convulsions.