CHLORPHENIRAMINE MALEATE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for CHLORPHENIRAMINE MALEATE (CHLORPHENIRAMINE MALEATE).
H1 receptor antagonist; competitively blocks histamine at H1 receptors, preventing histamine-mediated symptoms such as vasodilation, increased capillary permeability, and smooth muscle contraction.
| Metabolism | Hepatic via CYP450 (CYP2D6, CYP3A4); first-pass effect; major metabolites include desmethylchlorpheniramine. |
| Excretion | Renal: ~50% as metabolites; Fecal: negligible; Biliary: minor. |
| Half-life | Terminal elimination half-life: 12-15 hours (prolonged in hepatic impairment). |
| Protein binding | 72-96% bound to plasma proteins (primarily albumin). |
| Volume of Distribution | Vd: 3.0-7.0 L/kg (extensive tissue distribution). |
| Bioavailability | Oral: ~30-50% (first-pass metabolism); IM: ~100%. |
| Onset of Action | Oral: 0.5-1 hour; IM: ~30 minutes; IV: immediate. |
| Duration of Action | Oral: 4-6 hours (dose-dependent); sustained-release formulations: up to 12 hours. |
4 mg orally every 4-6 hours, not to exceed 24 mg per day; or 10-20 mg intramuscularly or intravenously as a single dose, not to exceed 40 mg per day.
| Dosage form | TABLET |
| Renal impairment | GFR 10-50 mL/min: administer every 6 hours; GFR <10 mL/min: administer every 8 hours. |
| Liver impairment | Child-Pugh Class C: reduce dose by 50% or administer every 12 hours; Class A or B: no adjustment necessary. |
| Pediatric use | Children 2-5 years: 1 mg orally every 4-6 hours, not to exceed 6 mg per day; Children 6-11 years: 2 mg orally every 4-6 hours, not to exceed 12 mg per day; Children ≥12 years: same as adult. |
| Geriatric use | Initiate at 4 mg orally every 8-12 hours due to increased risk of anticholinergic effects and sedation; maximum daily dose 12 mg. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for CHLORPHENIRAMINE MALEATE (CHLORPHENIRAMINE MALEATE).
| Breastfeeding | Chlorpheniramine is excreted into breast milk; M/P ratio not established. The American Academy of Pediatrics considers it compatible with breastfeeding, but caution is advised due to potential effects on milk production (anticholinergic effect may decrease milk supply) and infant sedation. Monitor infant for drowsiness or irritability. |
| Teratogenic Risk | FDA Pregnancy Category B. Animal studies have not demonstrated fetal risk, but no adequate controlled studies in pregnant women. First trimester: no known teratogenic effects; second and third trimesters: potential for anticholinergic effects, respiratory depression, or apnea in neonates if used near term. Avoid during labor and delivery due to possible adverse effects on uterine contractility. |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to chlorpheniramine or any component","Children younger than 2 years (risk of respiratory depression)","Asthma attack (acute)","MAOI therapy (concurrent or within 14 days)"]
| Precautions | ["May cause drowsiness and impair ability to drive or operate machinery","Use with caution in patients with asthma, COPD, or urinary retention","Avoid concomitant use with CNS depressants","Elderly patients more susceptible to anticholinergic effects"] |
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| Fetal Monitoring | Monitor maternal blood pressure and heart rate due to potential anticholinergic effects. In late pregnancy, assess fetal heart rate and uterine activity if used near term, especially with high doses. Neonatal monitoring for signs of anticholinergic toxicity or respiratory depression post-delivery. |
| Fertility Effects | Limited data; no known significant effects on fertility in humans. Animal studies have not shown impaired fertility. Anticholinergic effects may theoretically affect cervical mucus consistency, but clinical relevance is minimal. |