DIMETANE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for DIMETANE (DIMETANE).
Dimetane (brompheniramine) is a first-generation alkylamine antihistamine that competitively antagonizes histamine at H1 receptor sites, preventing histamine-mediated effects such as vasodilation, increased capillary permeability, and bronchoconstriction. It also has anticholinergic and sedative properties.
| Metabolism | Primarily hepatic via CYP450 enzymes (CYP2D6, CYP3A4). |
| Excretion | Primarily renal excretion of metabolites, with approximately 50% of a dose excreted in urine as unchanged drug and metabolites; biliary/fecal excretion is minor (< 10%). |
| Half-life | Terminal elimination half-life is approximately 12-15 hours in adults, necessitating twice-daily or three-times-daily dosing for continuous effect. |
| Protein binding | Approximately 95% bound to plasma proteins, mainly albumin. |
| Volume of Distribution | Volume of distribution (Vd) is approximately 1.5-2.0 L/kg, indicating extensive extravascular distribution. |
| Bioavailability | Oral bioavailability is approximately 70-80% due to first-pass metabolism. |
| Onset of Action | Oral: Onset of action occurs within 15-30 minutes; intramuscular: 10-20 minutes; intravenous: immediate (within minutes). |
| Duration of Action | Duration of action is 4-6 hours for most clinical effects, though some antihistaminic activity may persist up to 12 hours. |
| Molecular Weight | 348.48 |
1-2 tablets (4-8 mg chlorpheniramine maleate) orally every 4-6 hours, not to exceed 12 tablets (48 mg) in 24 hours.
| Dosage form | TABLET, EXTENDED RELEASE |
| Renal impairment | CrCl 30-50 mL/min: reduce dose by 50% or extend interval to every 6-8 hours; CrCl <30 mL/min: avoid use or use with caution at reduced frequency (e.g., every 8-12 hours). |
| Liver impairment | Child-Pugh Class A: no adjustment; Class B: reduce dose by 50% or use with caution; Class C: avoid use due to risk of accumulation. |
| Pediatric use | 5-11 years: 4 mg orally every 4-6 hours, max 16 mg/24 hours; 12 years and older: same as adult. |
| Geriatric use | Initial dose 4 mg orally every 6-8 hours; increase cautiously due to increased risk of anticholinergic effects and falls; limit maximum daily dose. |
| 1st trimester | Avoid. Antihistamines should be used only if clearly needed. Limited data in first trimester. |
| 2nd trimester | Use with caution. Consider possible sedative effects and potential for adverse effects. |
| 3rd trimester | Avoid near term; may increase risk of neonatal irritability or withdrawal. |
Clinical note
Comprehensive clinical and safety monograph for DIMETANE (DIMETANE).
| Placental transfer | Crosses placenta; degree not well quantified. |
| Breastfeeding | Small amounts pass into breast milk. May cause drowsiness in infant. Use lowest effective dose for shortest duration. |
| Lactation Rating |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to Dimetane or any componentNewborn or premature infantsBreastfeeding (relative) but caution
| Precautions | Sedation and CNS depression: caution with activities requiring alertness, Anticholinergic effects: exacerbation of narrow-angle glaucoma, urinary retention, prostatic hyperplasia, Respiratory depression: avoid in lower respiratory tract diseases (e.g., asthma, COPD), Elderly: increased risk of confusion, hypotension, falls, Pediatric use: paradoxical excitation, especially with overdose, Hepatic impairment: reduced clearance, possible increased toxicity, Pregnancy: Category C, use only if clearly needed |
| Food/Dietary | No specific food interactions. Alcohol should be avoided due to additive sedative effects. Grapefruit juice may increase absorption, but clinically significant interaction is unlikely. |
Loading safety data…
| L3 (Moderately Safe) |
| Teratogenic Risk | FDA Pregnancy Category B. First trimester: No evidence of increased malformation risk in human studies. Second/third trimester: Anticholinergic effects may cause neonatal tachycardia, irritability, and feeding difficulties. Use only if clearly needed. |
| Fetal Monitoring | Monitor maternal blood pressure and heart rate; assess fetal heart rate patterns if used near term for anticholinergic effects. |
| Fertility Effects | No known adverse effects on fertility in animal studies; human data limited. |
| Clinical Pearls | Dimetane (brompheniramine) is a first-generation alkylamine antihistamine with strong anticholinergic effects. It is effective for allergic rhinitis and urticaria but causes significant sedation. Avoid use in patients with narrow-angle glaucoma, prostatic hyperplasia, or urinary retention. Onset is 15-30 minutes, duration 4-6 hours. Use with caution in elderly due to fall risk. May interfere with allergy skin testing; discontinue 72 hours prior. |
| Patient Advice | Take exactly as prescribed; do not exceed recommended dose. · May cause drowsiness; avoid driving or operating heavy machinery until you know how you react. · Avoid alcohol and other sedatives as they can increase drowsiness. · Do not use with other antihistamines or cold medications without consulting doctor. · If you miss a dose, skip it; do not double up. · Contact doctor if symptoms worsen or do not improve after 1 week. |