EFIDAC 24 CHLORPHENIRAMINE MALEATE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for EFIDAC 24 CHLORPHENIRAMINE MALEATE (EFIDAC 24 CHLORPHENIRAMINE MALEATE).
Chlorpheniramine maleate is a first-generation alkylamine antihistamine that competitively antagonizes histamine at H1 receptor sites, preventing histamine-mediated allergic reactions. It also has anticholinergic and sedative properties due to central H1 receptor blockade.
| Metabolism | Primarily metabolized by CYP450 enzymes, including CYP2D6. Metabolites undergo further conjugation and renal excretion. |
| Excretion | Renal excretion of unchanged drug and metabolites accounts for approximately 70-80% of elimination, with about 20-30% excreted via feces (biliary). |
| Half-life | Terminal elimination half-life ranges from 14 to 25 hours (mean 20 hours) in adults; prolonged in hepatic or renal impairment (up to 50-60 hours in cirrhosis). |
| Protein binding | Approximately 70% bound, primarily to albumin. |
| Volume of Distribution | Apparent Vd: 3-4 L/kg, indicating extensive tissue distribution. |
| Bioavailability | Oral bioavailability is approximately 40-60% due to first-pass metabolism. |
| Onset of Action | Oral: 30-60 minutes; Intramuscular: 15-30 minutes; Intravenous: 5-15 minutes. |
| Duration of Action | Oral: 4-6 hours; Intramuscular/Intravenous: 4-6 hours; sustained-release formulations (e.g., EFIDAC 24) extend to 24 hours due to prolonged absorption. |
4 mg orally every 4-6 hours; maximum 24 mg/day.
| Dosage form | TABLET, EXTENDED RELEASE |
| Renal impairment | GFR 10-50 mL/min: administer every 6-8 hours; GFR <10 mL/min: administer every 8-12 hours. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B or C: reduce dose by 50% or increase interval. |
| Pediatric use | 2-5 years: 1 mg every 4-6 hours, max 6 mg/day; 6-11 years: 2 mg every 4-6 hours, max 12 mg/day; ≥12 years: adult dose. |
| Geriatric use | Initiate at 4 mg every 8-12 hours due to increased sensitivity and risk of anticholinergic effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for EFIDAC 24 CHLORPHENIRAMINE MALEATE (EFIDAC 24 CHLORPHENIRAMINE MALEATE).
| Breastfeeding | Chlorpheniramine is excreted into breast milk in small amounts. M/P ratio not established. Use with caution; may cause irritability, drowsiness, or decreased feeding in nursing infants. Consider alternative antihistamines with lower milk excretion (e.g., loratadine, cetirizine). |
| Teratogenic Risk | FDA Pregnancy Category B. First trimester: No evidence of increased risk of major congenital malformations in human studies; however, anticholinergic effects may be significant. Second and third trimesters: Use with caution near term due to potential for respiratory depression and paradoxical excitability in neonates. High doses may cause uterine hypertonicity or decreased uterine contractility. |
■ FDA Black Box Warning
No FDA black box warnings.
| Serious Effects |
["Hypersensitivity to chlorpheniramine or any other antihistamines of similar structure","Concurrent use with MAO inhibitors (MAOIs) within 14 days","Premature and full-term neonates","Narrow-angle glaucoma","Bladder neck obstruction or prostatic hyperplasia","Asthma attack (acute)"]
| Precautions | ["Avoid use in patients with asthma, COPD, or other lower respiratory tract diseases due to anticholinergic effects (thickening of secretions).","Caution in elderly patients due to increased risk of sedation, dizziness, and hypotension.","May impair cognitive and motor function; caution when driving or operating machinery.","Avoid use with other CNS depressants (e.g., alcohol, benzodiazepines) due to additive sedation.","Use cautiously in patients with cardiovascular disease (e.g., hypertension, arrhythmias) due to potential anticholinergic effects.","Do not use in premature or full-term neonates due to risk of paradoxical excitation and convulsions."] |
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| Fetal Monitoring | Maternal: Monitor for anticholinergic effects (dry mouth, blurred vision, urinary retention) and CNS effects (drowsiness, dizziness). Fetal/neonatal: Monitor for respiratory depression, paradoxical excitability if used near term. |
| Fertility Effects | No well-documented effects on human fertility. Animal studies have not demonstrated impaired fertility. Anticholinergic effects may theoretically influence cervical mucus or vaginal secretions. |