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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for DIMETANE (DIMETANE).
| Breastfeeding | Present in breast milk in small amounts; M/P ratio not reported. May cause drowsiness or irritability in nursing infants. Use caution; consider alternative antihistamines with lower risk. |
| 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 |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to brompheniramine or any component","Lower respiratory tract symptoms (e.g., asthma, COPD)","Neonates and premature infants","Concurrent MAO inhibitor therapy","Narrow-angle glaucoma","Symptomatic prostatic hypertrophy","Urinary retention","Breastfeeding (avoid if possible)"]
| 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"] |
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| 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. |