What is the recommended dosage of Histex (Diphenhydramine) 2.5 MG/5ML Syrup for a 9-year-old male patient weighing 53.4 pounds for cough?

Appropriate Dosing of Histex (Diphenhydramine) 2.5 MG/5ML Syrup for a 9-Year-Old Child

The prescribed dose of 2.5 mL (1.25 mg) of Histex (diphenhydramine) syrup every 6 hours as needed for cough in a 9-year-old child weighing 53.4 pounds is significantly lower than recommended dosing guidelines and may be insufficient for symptom relief.

Recommended Dosing for Diphenhydramine in Children

• For children aged 1-9 years, the FDA-approved dosage for diphenhydramine is 4.4-8.8 mg/kg/day, not to exceed 150 mg/day 1
• To reduce the risk of toxicity, the Advisory Committee on Immunization Practices (ACIP) recommends prescribing 5 mg/kg/day, not exceeding 150 mg daily 1
• For a child weighing 53.4 pounds (approximately 24.2 kg), the appropriate daily dose would be approximately 121 mg (5 mg/kg × 24.2 kg) 1
• This translates to approximately 30 mg per dose when given every 6 hours (121 mg ÷ 4 doses) 1

Analysis of Current Prescription

• The prescribed dose of 2.5 mL of Histex 2.5 MG/5ML provides only 1.25 mg of diphenhydramine per dose 1
• This dose is significantly below the recommended range and represents only about 4% of the appropriate weight-based dose 1
• At this low dose, the medication is unlikely to provide effective symptom relief for cough 2

Evidence for Diphenhydramine's Efficacy in Cough

• Research shows that diphenhydramine can significantly inhibit cough reflex sensitivity in subjects with acute viral respiratory tract infections 2
• A study demonstrated a significant increase in cough threshold after diphenhydramine administration compared to placebo in patients with acute cough 2
• However, these benefits were observed at standard therapeutic doses, not the subtherapeutic dose currently prescribed 2

Potential Concerns with Diphenhydramine Use

• Common side effects at therapeutic doses include nervousness, insomnia, and hyperactivity in approximately 9.3% of children 3
• Somnolence may occur in approximately 7.5% of children taking diphenhydramine 3
• The current low dose is unlikely to cause these side effects but is also unlikely to provide therapeutic benefit 3, 2

Alternative Approaches for Cough Management

• For children with cough, honey has been shown to probably relieve symptoms better than diphenhydramine and placebo in multiple studies 3
• Honey is suitable for children over 12 months of age and may be a safer alternative with fewer side effects 3
• Adequate hydration, humidification of room air, and nasal saline drops may help ease respiratory symptoms 4

Recommended Action

• The diphenhydramine dose should be adjusted to approximately 30 mg (60 mL of the 2.5 MG/5ML formulation) every 6 hours as needed for this 9-year-old child weighing 53.4 pounds, not to exceed 120 mg daily 1
• If this concentration makes dosing difficult, consider requesting a higher concentration formulation to make administration more practical 5
• Monitor for potential side effects including somnolence, nervousness, or hyperactivity 3
• Consider discussing alternative cough management strategies with the prescriber if appropriate 3