What is the recommended milligrams per kilogram (mg/kg) dosing of diphenhydramine for a 21-month-old patient experiencing an allergic reaction?

From the Guidelines

For a 21-month-old child with an allergic reaction, the recommended diphenhydramine dosage is 1-2 mg/kg/dose, administered every 6 hours as needed, with a maximum single dose not exceeding 50 mg, regardless of weight, as supported by the most recent guidelines 1. When calculating the dose, you should use the child's actual weight in kilograms. For example, if the child weighs 12 kg, an appropriate dose would be 12-24 mg.

• Diphenhydramine can be given orally or, in more severe cases, intravenously.
• Diphenhydramine works by blocking histamine receptors, reducing symptoms like itching, hives, and swelling.
• Side effects may include drowsiness, dry mouth, and occasionally paradoxical excitation in young children. If the allergic reaction involves respiratory distress, angioedema, or other signs of anaphylaxis, epinephrine should be administered immediately as diphenhydramine alone is not sufficient for treating anaphylaxis, as emphasized in the guidelines 1.
• The guidelines also recommend considering adjunctive treatment with bronchodilators, such as albuterol, and supplemental oxygen therapy if necessary.
• It is essential to monitor the child's response to treatment and adjust the dosage or add other medications as needed, always prioritizing the child's safety and well-being 1.

From the FDA Drug Label

DOSAGE AND ADMINISTRATION: ... Pediatric Patients, other than premature infants and neonates: 5 mg/kg/24 hr or 150 mg/m 2/24 hr. For a 21-month-old patient with an allergic reaction, the recommended dosing of diphenhydramine is 5 mg/kg/24 hr.

• The dose should be individualized according to the needs and response of the patient.
• The maximum daily dosage is 300 mg.
• The dose should be divided into four doses, administered intravenously at a rate generally not exceeding 25 mg/min 2

From the Research

Dosing Information for Diphenhydramine

• The provided studies do not specifically mention the mg/kg dosing of diphenhydramine for a 21-month-old patient with an allergic reaction.
• However, the studies emphasize the importance of epinephrine as the first-line treatment for anaphylaxis 3, 4, 5, 6, 7.
• Antihistamines, such as diphenhydramine, may be used as adjunctive therapy, but their role in anaphylaxis management is not as well-established as epinephrine 5, 7.
• The studies suggest that antihistamines may be useful in preventing recurrence of anaphylaxis, but they have a delayed onset of action compared to epinephrine 5, 6.
• It is essential to note that the treatment of anaphylaxis should be guided by established protocols and guidelines, and the use of diphenhydramine should be determined on a case-by-case basis, considering the severity of the reaction and the patient's medical history 3, 4, 6, 7.

Treatment of Anaphylaxis

• Epinephrine is the cornerstone of treatment for anaphylaxis, and its early administration is critical to prevent a potentially fatal outcome 4, 5, 6, 7.
• The use of antihistamines and corticosteroids may be considered as adjunctive therapy, but their role in anaphylaxis management is not as well-established as epinephrine 5, 7.
• Fluid resuscitation with balanced electrolyte solutions and high-flow oxygen are also fundamental in the treatment of anaphylaxis 6.

Patient-Specific Considerations

• The treatment of anaphylaxis should be individualized, taking into account the patient's age, medical history, and the severity of the reaction 3, 6, 7.
• In pediatric patients, such as the 21-month-old patient in question, the treatment of anaphylaxis should be guided by established protocols and guidelines, and the use of diphenhydramine should be determined on a case-by-case basis 7.