DIMETANE-DX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for DIMETANE-DX (DIMETANE-DX).
Dimetane-DX contains brompheniramine (first-generation antihistamine) and dextromethorphan (NMDA receptor antagonist and sigma-1 agonist). Brompheniramine antagonizes histamine at H1 receptors, reducing allergic symptoms; dextromethorphan suppresses cough by acting on the cough center in the medulla oblongata via NMDA receptor antagonism and sigma-1 receptor activation.
| Metabolism | Brompheniramine is hepatically metabolized via CYP450 enzymes (primarily CYP2D6). Dextromethorphan is extensively metabolized by CYP2D6 to dextrorphan (active metabolite). |
| Excretion | Renal: 50-70% (brompheniramine) as metabolites and unchanged drug; guaifenesin metabolites primarily renal; dextromethorphan and metabolites renal. Biliary/fecal: minor. |
| Half-life | Brompheniramine: 25-30 hours; guaifenesin: 1 hour; dextromethorphan: 2-4 hours (CYP2D6 extensive metabolizers) or 20-40 hours (poor metabolizers). |
| Protein binding | Brompheniramine: 50-60% to albumin; guaifenesin: <5%; dextromethorphan: 60-70% to albumin. |
| Volume of Distribution | Brompheniramine: 1.5-2.0 L/kg; guaifenesin: 0.5-1.0 L/kg; dextromethorphan: 5-10 L/kg. |
| Bioavailability | Oral: brompheniramine 50-70%, guaifenesin 70-90%, dextromethorphan 40-60% (first-pass metabolism). |
| Onset of Action | Oral: brompheniramine 15-30 minutes, guaifenesin 30-60 minutes, dextromethorphan 15-30 minutes. |
| Duration of Action | Oral: brompheniramine 4-6 hours (up to 12 hours for sustained-release), guaifenesin 4-6 hours, dextromethorphan 4-6 hours. |
| Molecular Weight | 390.5 |
Adults and children ≥12 years: One tablet (brompheniramine 4 mg, dextromethorphan 10 mg, phenylephrine 10 mg) orally every 4 hours as needed, not to exceed 4 doses in 24 hours.
| Dosage form | SYRUP |
| Renal impairment | eGFR 30–59 mL/min: Administer with caution and reduce frequency to every 6 hours. eGFR <30 mL/min: Avoid use due to risk of accumulation of dextromethorphan and phenylephrine. |
| Liver impairment | Child-Pugh Class A: No adjustment. Child-Pugh Class B: Reduce dosing interval to every 8 hours; use with caution. Child-Pugh Class C: Contraindicated due to extensive first-pass metabolism. |
| Pediatric use | Children 6–11 years: 5 mL (half the adult dose) of liquid formulation (brompheniramine 2 mg, dextromethorphan 5 mg, phenylephrine 5 mg per 5 mL) orally every 4 hours, max 4 doses/day. Children 2–5 years: 2.5 mL orally every 4 hours, max 4 doses/day. Children <2 years: Contraindicated. |
| Geriatric use | Age ≥65 years: Initiate at half the adult dose (e.g., one tablet every 8 hours) due to increased anticholinergic effects and risk of urinary retention, constipation, and dizziness. Avoid in frail elderly or those with cognitive impairment. |
| 1st trimester | Avoid in first trimester due to potential teratogenic effects (cleft palate, neural tube defects) associated with decongestants and antihistamines; limited data on dextromethorphan. |
| 2nd trimester | Use with caution; chlorpheniramine is preferred antihistamine but Dimetane-DX contains brompheniramine which may be safer than others; dextromethorphan appears safe but data limited. |
| 3rd trimester | Avoid near term due to risk of neonatal respiratory depression from dextromethorphan and potential withdrawal symptoms from brompheniramine. |
Clinical note
Comprehensive clinical and safety monograph for DIMETANE-DX (DIMETANE-DX).
| Placental transfer | Both brompheniramine and dextromethorphan cross the placenta; brompheniramine has evidence of placental transfer in animal studies; dextromethorphan crosses human placenta. |
| Breastfeeding | Brompheniramine and dextromethorphan are excreted into breast milk in small amounts; antihistamines may cause infant irritability or drowsiness; dextromethorphan is considered compatible but monitor infant for sedation. Avoid due to potential anticholinergic effects in infant. |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to brompheniramine, dextromethorphan, or any componentMAOI therapy (current or within 14 days)Severe hypertension or coronary artery disease (brompheniramine)Narrow-angle glaucomaUrinary retention (e.g., from prostatic hypertrophy)Asthma attack (brompheniramine may thicken secretions)Children <6 years due to risk of respiratory depression
| Precautions | Do not use with MAOIs or for 2 weeks after stopping MAOIs due to risk of serotonin syndrome (dextromethorphan)., Avoid use in patients with asthma, chronic bronchitis, emphysema, or persistent cough (may suppress cough reflex)., Use with caution in patients with glaucoma, prostatic hyperplasia, urinary retention, or hypertension (brompheniramine anticholinergic effects)., CNS depression risk: may cause drowsiness; avoid alcohol or other sedatives. |
| Food/Dietary | Avoid concurrent use of tyramine-rich foods (e.g., aged cheeses, cured meats, soy sauce, fermented foods) due to risk of hypertensive crisis with sympathomimetic (phenylephrine). Grapefruit juice may increase dextromethorphan levels; avoid large amounts. |
Loading safety data…
| Lactation Rating | L3 - Moderately Safe |
| Teratogenic Risk | Dimetane-DX contains brompheniramine (antihistamine) and dextromethorphan (antitussive). First trimester: Limited human data; animal studies show no teratogenicity at therapeutic doses. Second and third trimesters: Avoid due to risk of neonatal respiratory depression, withdrawal symptoms, and anticholinergic effects. Dextromethorphan: No clear teratogenic risk, but avoid use. Overall: Contraindicated in pregnancy unless benefit outweighs risk. |
| Fetal Monitoring | Monitor for maternal sedation, hypotension, and anticholinergic effects. Fetal monitoring for heart rate and activity if used near term. In neonates, observe for respiratory depression, poor feeding, and withdrawal symptoms. |
| Fertility Effects | Limited data. Antihistamines may theoretically affect sperm function or ovulation. Dextromethorphan has no known significant fertility effects. Avoid use in couples actively trying to conceive due to lack of safety data. |
| Clinical Pearls | DIMETANE-DX combines brompheniramine (first-generation antihistamine), phenylephrine (decongestant), and dextromethorphan (antitussive). Avoid in hypertension, MAOI use, or asthma. Monitor for CNS depression and anticholinergic effects. |
| Patient Advice | Do not drive or operate machinery until you know how this medication affects you; it may cause drowsiness or dizziness. · Avoid alcohol and other sedatives; they increase sedation and CNS depression. · Do not exceed recommended dosage or use for more than 7 days for cough. · Stop use and consult a doctor if symptoms persist or worsen, or if you develop fever, rash, or persistent headache. · Inform your healthcare provider if you have high blood pressure, heart disease, glaucoma, or urinary retention. |