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. |
| Molecular Weight | 390.87 |
| Action Class | First-generation antihistamine (H1-receptor antagonist) |
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 | Avoid use; limited data, but antihistamines generally not recommended first trimester unless essential. |
| 2nd trimester | Use only if clearly needed; risk unclear. |
| 3rd trimester | Avoid near term; may cause respiratory depression or withdrawal in neonate. |
Clinical note
Comprehensive clinical and safety monograph for EFIDAC 24 CHLORPHENIRAMINE MALEATE (EFIDAC 24 CHLORPHENIRAMINE MALEATE).
| Placental transfer | Crosses placenta; extent unknown. |
| Breastfeeding | Small amounts excreted in breast milk; may cause irritability, drowsiness in infant. Caution in preterm or newborns. |
| Lactation Rating |
■ FDA Black Box Warning
No FDA black box warnings.
| Common Effects | Drowsiness, Dizziness, Dry mouth, nose, and throat, Blurred vision, Urinary retention, Constipation, Nausea, Headache, Fatigue |
| Serious Effects | Respiratory depression (especially in overdose or with CNS depressants), Seizures, Cardiac arrhythmias (e.g., QT prolongation, torsades de pointes), Severe hypotension, Acute dystonic reactions, Anaphylaxis, Agranulocytosis (rare) |
Hypersensitivity to chlorpheniramineNewborn or premature infantsConcurrent MAOI therapyAcute asthma attack
| 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. |
Loading safety data…
| L3 (Moderately Safe) |
| 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. |
| 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. |
| Food/Dietary | No significant food interactions known; however, taking with food may reduce gastrointestinal upset. Avoid grapefruit juice as it may alter drug metabolism (minimal for chlorpheniramine, but precautionary). |
| Clinical Pearls | Chlorpheniramine is a first-generation alkylamine antihistamine with strong sedative properties; avoid in elderly due to anticholinergic effects and fall risk. Use with caution in patients with glaucoma, prostatic hypertrophy, or urinary retention. May cause paradoxic excitation in children. |
| Patient Advice | May cause drowsiness; avoid driving or operating machinery until you know how this drug affects you. · Avoid alcohol and other CNS depressants (e.g., sedatives, tranquilizers) as they can increase sedation. · Do not take with other antihistamines or cold/flu products without consulting a doctor. · Take exactly as directed; do not exceed recommended dose or duration. · Notify your doctor if you have glaucoma, trouble urinating, or an enlarged prostate before use. |