What is the dose and drip rate of Phenytoin (antiepileptic medication) in 100 ml of Normal Saline (NS) for a patient?

From the Guidelines

For Phenytoin administration in 100 ml of Normal Saline, the recommended dose is 20 mg/kg, infused over 10-20 min, with a maximum rate of 1 mg/kg per min, and the drip rate can be calculated as 100 ml / 10-20 min, which is approximately 5-10 ml/min. To calculate the dose and drip rate, we need to consider the patient's weight and the recommended infusion time. According to the study 1, the recommended infusion time is 10-20 min, and the maximum rate is 1 mg/kg per min. For a patient weighing 70 kg, the dose would be 20 mg/kg x 70 kg = 1400 mg. To administer this dose over 10-20 min, we can calculate the drip rate as follows:

• 100 ml / 10 min = 10 ml/min
• 100 ml / 20 min = 5 ml/min So, the drip rate would be approximately 5-10 ml/min. It's essential to monitor the patient's heart rate, blood pressure, and oxygen saturation during infusion, as Phenytoin can cause hypotension, arrhythmias, and respiratory depression. Additionally, the solution should be prepared immediately before administration and used with an in-line filter to prevent precipitation. Some key points to consider when administering Phenytoin include:
• The solution should be diluted in Normal Saline to avoid precipitation
• The infusion rate should not exceed 1 mg/kg per min
• Continuous cardiac monitoring is necessary during infusion
• Blood pressure, heart rate, and infusion site should be monitored throughout administration
• Phenytoin can cause local irritation and "Purple Glove Syndrome" if extravasation occurs.

From the FDA Drug Label

The rate of intravenous administration should not exceed 50 mg per minute in adults and 1 to 3 mg/kg/min (or 50 mg per minute, whichever is slower) in pediatric patients. Phenytoin Sodium Injection can be given diluted with normal saline The addition of parenteral Phenytoin Sodium Injection to dextrose and dextrose-containing solutions should be avoided due to lack of solubility and resultant precipitation For infusion administration, parenteral Phenytoin Sodium Injection should be diluted in normal saline with the final concentration of phenytoin sodium in the solution no less than 5 mg/mL.

To calculate the dose and drip rate of Phenytoin in 100 ml of Normal Saline (NS), we need to know the patient's weight.

• The maximum dose is 50 mg per minute in adults and 1 to 3 mg/kg/min (or 50 mg per minute, whichever is slower) in pediatric patients.
• Assuming a dose of 50 mg per minute and a volume of 100 ml, the drip rate can be calculated as follows:

• Dose (mg): 50 mg/min
• Volume (ml): 100 ml
• Time (min): unknown

• To find the time, we can use the formula: Time (min) = Volume (ml) / Drip rate (ml/min)
• However, the drip rate is not explicitly stated in the question.
• Assuming a standard drip rate of 10-20 ml/min for a 100 ml solution, the time can be estimated as follows:

• Drip rate (ml/min): 10-20 ml/min
• Time (min): 100 ml / 10-20 ml/min = 5-10 min

• Therefore, the estimated drip rate is 10-20 ml/min, and the estimated time is 5-10 min.
• However, please note that this calculation is an estimate and may vary depending on the specific patient and clinical situation.
• It is always best to consult with a healthcare professional for specific dosing and administration instructions 2, 2.

From the Research

Phenytoin Dose and Drip Rate Calculation

To calculate the dose and drip rate of Phenytoin in 100 ml of Normal Saline (NS), we need to consider the recommended loading dose and infusion rate.

• The recommended loading dose of Phenytoin is 18-20 mg/kg, administered over 20-30 minutes 3, 4.
• The infusion rate can be calculated based on the loading dose and the desired infusion time.

Calculation Example

Assuming a patient weighs 70 kg and requires a loading dose of 18 mg/kg, the total dose would be:

• 18 mg/kg x 70 kg = 1260 mg
• To administer this dose over 20-30 minutes, the infusion rate would be:
• 1260 mg / 20 minutes = 63 mg/minute (using 20 minutes)
• 1260 mg / 30 minutes = 42 mg/minute (using 30 minutes)

Drip Rate Calculation

To calculate the drip rate in drops per minute, we need to know the concentration of the solution and the drop factor of the infusion set.

• Assuming a concentration of 50 mg/ml (500 mg in 10 ml) and a drop factor of 60 drops/ml, the drip rate would be:
• 63 mg/minute / 50 mg/ml = 1.26 ml/minute (using 20 minutes)
• 1.26 ml/minute x 60 drops/ml = 75.6 drops/minute (using 20 minutes)
• 42 mg/minute / 50 mg/ml = 0.84 ml/minute (using 30 minutes)
• 0.84 ml/minute x 60 drops/ml = 50.4 drops/minute (using 30 minutes)

Considerations

When administering Phenytoin, it is essential to monitor the patient's cardiac rhythm, blood pressure, and respiratory rate, as high concentrations and rapid infusion rates can cause cardiovascular complications 5, 3, 6.

• The recommended infusion rate should not exceed 50 mg/minute 3, 6.
• The patient's serum Phenytoin concentrations should be monitored to ensure therapeutic levels are achieved and maintained 3, 7, 4.