Active Ingredients in Over-the-Counter Dimetapp
Over-the-counter Dimetapp contains brompheniramine maleate (an antihistamine) and phenylephrine hydrochloride (a decongestant) as its active ingredients. 1, 2
Specific Formulation Details
- Brompheniramine maleate is a first-generation antihistamine that blocks histamine H1 receptors to reduce sneezing, itching, and rhinorrhea (runny nose) 1
- Phenylephrine hydrochloride is an oral decongestant that acts as a direct α-adrenergic agonist, causing vasoconstriction to reduce nasal congestion 1
- The typical OTC Dimetapp formulation contains 4 mg of brompheniramine maleate per dose 1, 2
- Some Dimetapp formulations may also include dextromethorphan hydrobromide (a cough suppressant) in addition to the antihistamine-decongestant combination 2, 3
Important Clinical Considerations
First-generation antihistamines like brompheniramine carry significant sedation risks and anticholinergic side effects that cannot be eliminated by bedtime-only dosing due to prolonged half-life. 1
- Brompheniramine has a plasma half-life of approximately 24.9 hours, leading to persistent CNS effects including impaired school and driving performance 1
- Sedation rates with brompheniramine range from 24-45% in clinical studies 1
- Anticholinergic effects include dry mouth, constipation, urinary retention, and increased risk of narrow-angle glaucoma, particularly in older adults 1
Efficacy and Safety Concerns
The efficacy of phenylephrine as an oral decongestant has not been well established, as it is extensively metabolized in the gut and appears less effective than pseudoephedrine. 1
- Phenylephrine was substituted for pseudoephedrine in many OTC products due to methamphetamine production concerns, not superior efficacy 1
- Oral decongestants can cause insomnia, loss of appetite, irritability, and palpitations 1
- Blood pressure elevation is rarely noted in normotensive patients but may occur in those with controlled hypertension, requiring monitoring 1
Pediatric Safety Warning
OTC cough and cold medications containing these ingredients should generally be avoided in children below 6 years of age due to lack of proven efficacy and potential toxicity. 1
- Between 1969-2006, there were 4 fatalities associated with phenylephrine and 9 with brompheniramine in children ≤6 years old 1
- Drug overdose and toxicity commonly resulted from use of multiple products, medication errors, and accidental exposures 1
- Controlled trials have shown antihistamine-decongestant combinations are not effective for upper respiratory tract infections in young children 1