Calculating Pediatric Promethazine Dosage Based on Body Surface Area (BSA)

Promethazine (Phenergan) is a commonly used medication for various conditions, including allergies, nausea, and vomiting. However, when administering it to pediatric patients, the dosage needs to be carefully calculated, often based on the child’s Body Surface Area (BSA) to ensure their safety and effectiveness of the treatment.

Understanding BSA and Dosage Calculation

A health care provider may order promethazine for a child, and the BSA plays a crucial role in determining the appropriate dosage. BSA is a method used to calculate the body’s total surface area, which helps in more accurate medication dosing for children.

Pediatric Dosage Considerations

In pediatric medicine, it’s essential to calculate medication dosages with precision to avoid under or overdosing, as children can be more sensitive to medications than adults. The usual adult dose of promethazine is 25 mg, but in pediatrics, the dose needs to be tailored to the individual’s characteristics.

Body Surface Area (BSA) Calculation

BSA is a valuable parameter for determining pediatric dosages. It’s calculated using various formulas, and one of the most commonly employed methods is the Mosteller formula. This formula takes into account the child’s weight and height, and it can be represented as follows:

BSA (m²) = √[weight (kg) x height (cm) / 3600]

Example Calculation

Let’s consider a case where a health care provider prescribes promethazine for a child with a BSA of 1.2 m². To determine the correct dosage, we’ll use the usual adult dose of 25 mg and adjust it based on the child’s BSA.

Calculating the Pediatric Dosage

To calculate the pediatric dosage, we’ll use the BSA value of 1.2 m²:

Pediatric Dosage = Usual Adult Dose (25 mg) x BSA (1.2 m²)

Pediatric Dosage = 25 mg x 1.2

Pediatric Dosage = 30 mg

The nurse, following the order, would administer 30 mg of promethazine to the child.

Precision in Pediatric Medication Administration

Pediatric medication dosing is highly specialized to ensure the safety and well-being of the young patients. It’s crucial for health care providers and nurses to be well-versed in these calculations and to follow the prescribed dosage guidelines accurately. Factors like BSA, weight, and age are all considered in this process.


Administering medications to pediatric patients requires careful consideration and precise dosage calculations. In the case of promethazine (Phenergan), the child’s Body Surface Area (BSA) is used to determine the appropriate dosage. The BSA is calculated using formulas like the Mosteller formula, and the dosage is adjusted based on the child’s unique characteristics. This ensures that the child receives the correct amount of medication for their specific needs while minimizing the risk of adverse effects. Health care providers and nurses play a crucial role in this process, ensuring the safe and effective use of medications in pediatric patients.


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