Active Ingredient in Original Dimetapp
The original Dimetapp contained brompheniramine maleate as its primary active antihistamine ingredient, typically combined with phenylpropanolamine (later replaced by pseudoephedrine) as a decongestant 1, 2.
Historical Formulation Components
Brompheniramine maleate served as the first-generation antihistamine in Dimetapp formulations, functioning as an H1-receptor antagonist with anticholinergic (drying) and sedative properties 2. This alkylamine-class antihistamine was specifically chosen for its ability to:
- Block histamine receptors on effector cells, antagonizing allergic responses including vasodilation, increased vascular permeability, and mucus secretion 2
- Provide superior control of rhinorrhea compared to second-generation antihistamines due to its anticholinergic effects 1
- Achieve peak plasma concentration approximately 5 hours after oral administration, with urinary excretion as the major elimination route 2
Combination Formulation Rationale
The American College of Chest Physicians recognizes that first-generation antihistamines like brompheniramine are preferred over newer generation antihistamines for treating cold symptoms specifically because of their anticholinergic properties 1. When combined with decongestants:
- Brompheniramine addresses histamine-mediated symptoms (sneezing, itching, rhinorrhea) while the decongestant component (pseudoephedrine or phenylpropanolamine) targets nasal congestion through α-sympathetic receptor-mediated vasoconstriction 3, 2
- This combination provides complementary effects with enhanced symptom relief compared to either agent alone 3, 4
Clinical Evidence for Brompheniramine
A large randomized controlled trial demonstrated that brompheniramine 12 mg twice daily significantly reduced nasal secretion weights, rhinorrhea scores, sneeze counts, and total symptom scores in rhinovirus colds compared to placebo (P < 0.03 for most measures) 5.
Important Safety Consideration
First-generation antihistamines like brompheniramine can cause performance impairment in school and driving that may exist without subjective awareness of sedation, and these effects cannot be eliminated by bedtime-only administration due to prolonged plasma half-life 1.