Diphenhydramine (Histex) Dosing for a 13-Year-Old Weighing 72.4 Pounds
Yes, diphenhydramine (Histex) is appropriate for a 13-year-old weighing 72.4 pounds (approximately 33 kg), with a recommended dose of 25 mg every 4-6 hours, not exceeding 6 doses in 24 hours. 1
Dosage Recommendations
- For children 6 to under 12 years of age, the FDA-approved dose is 10 mL (25 mg) 1
- For children over 12 years of age, the FDA-approved dose is 10 mL (25 mg) to 20 mL (50 mg) 1
- Since this 13-year-old weighs 72.4 pounds (approximately 33 kg), which is less than 40 kg (88 pounds), the lower end of the dosing range (25 mg) is more appropriate 2
- Do not exceed 6 doses in 24 hours as per FDA labeling 1
- Administer every 4 to 6 hours as needed 1
Safety Considerations
- Diphenhydramine may cause drowsiness, which is more pronounced in children than adults 3
- Consider administering the dose in the evening if drowsiness occurs to minimize impact on daily activities 3
- Monitor for potential side effects including:
Toxicity Concerns
- The toxic threshold for diphenhydramine in children 6 years and older is 7.5 mg/kg or 300 mg (whichever is less) 6
- For this 13-year-old weighing approximately 33 kg, the toxic threshold would be approximately 247.5 mg 6
- The recommended dose of 25 mg is well below this toxic threshold and is safe when used as directed 1, 6
Alternative Considerations
- Second-generation antihistamines (like cetirizine) may be preferable alternatives with fewer sedative effects 7
- If diphenhydramine is being used for sleep, be aware that it is not recommended for long-term use as a sleep aid 5
Important Precautions
- Avoid combining with other medications that cause sedation without medical supervision 4
- Do not exceed the recommended dose, as diphenhydramine toxicity can cause serious adverse effects including cardiac toxicity 7
- If the child experiences any unusual symptoms such as agitation, hallucinations, abnormal muscle movements, or severe drowsiness, discontinue use and seek medical attention 6