CLEMASTINE FUMARATE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for CLEMASTINE FUMARATE (CLEMASTINE FUMARATE).
Clemastine fumarate is a competitive antagonist of histamine at H1-receptor sites, suppressing histamine-induced vasodilation, increased capillary permeability, bronchoconstriction, and pruritus. It also exhibits anticholinergic and sedative effects.
| Metabolism | Metabolized extensively in the liver via hepatic microsomal enzymes, primarily CYP450 system (specific isoenzymes not well characterized). |
| Excretion | Primarily renal (45-55% as unchanged drug and metabolites) and fecal (30-40%), with biliary excretion contributing minorly. |
| Half-life | Terminal elimination half-life: 21 ± 6 hours. Provides sustained antihistamine effect, allowing twice-daily dosing. |
| Protein binding | Approximately 95-99% bound to plasma proteins, primarily albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Vd: 4.4-5.0 L/kg, indicating extensive tissue distribution beyond plasma volume. |
| Bioavailability | Oral: 40-60% due to first-pass metabolism; intramuscular: ~100%. |
| Onset of Action | Oral: 30-60 minutes; intramuscular: 15-30 minutes; intravenous: 5-10 minutes. |
| Duration of Action | Oral: 12-24 hours; parenteral: 8-12 hours. Duration may be shorter in hepatic impairment. |
| Molecular Weight | 389.4 |
1.34 mg orally twice daily; max 8.04 mg/day
| Dosage form | SYRUP |
| Renal impairment | No adjustment required for GFR > 10 mL/min; avoid use if GFR < 10 mL/min |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: avoid use |
| Pediatric use | 6-12 years: 0.67 mg orally twice daily; >12 years: same as adult |
| Geriatric use | Initiate at 0.67 mg orally twice daily; avoid if possible due to anticholinergic effects |
| 1st trimester | Limited human data; animal studies show no evidence of teratogenicity but avoid unless clearly needed. |
| 2nd trimester | Use only if potential benefit justifies risk; no known fetal harm. |
| 3rd trimester | Avoid near term due to potential anticholinergic effects (e.g., respiratory depression) in neonate. |
Clinical note
Comprehensive clinical and safety monograph for CLEMASTINE FUMARATE (CLEMASTINE FUMARATE).
| Placental transfer | Crosses placenta; extent not well quantified. |
| Breastfeeding | Excreted in breast milk in small amounts; may cause irritability or drowsiness in infant; use caution, especially in premature infants. |
| Lactation Rating |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to clemastine or other antihistaminesSevere hepatic impairmentConcurrent use with MAOIsAcute asthma attack
| Precautions | CNS depression: May impair mental alertness, especially with alcohol or other sedatives., Anticholinergic effects: Caution in patients with glaucoma, prostatic hypertrophy, or urinary retention., Use in elderly: Increased risk of sedation, confusion, and falls., Dermatologic: Not recommended for topical use except as specifically formulated. |
| Food/Dietary | No specific food interactions; however, intake with food may delay absorption. Alcohol consumption potentiates CNS depression and should be strictly avoided. |
Loading safety data…
| L3 (Moderately Safe) |
| Teratogenic Risk | Limited human data; animal studies show no consistent teratogenicity. In first trimester, use only if clearly needed; second and third trimester use associated with risk of neonatal irritability, tremors, and respiratory depression. Avoid near term due to potential anticholinergic effects. |
| Fetal Monitoring | Monitor maternal blood pressure, heart rate, and anticholinergic effects. Fetal monitoring not routinely required but consider nonstress test if maternal adverse effects or preterm labor symptoms occur. |
| Fertility Effects | No definitive data on human fertility; animal studies show no impairment at therapeutic doses. Anticholinergic effects may theoretically affect cervical mucus or ovulation, but clinical significance is unknown. |
| Clinical Pearls |
| Clemmastine fumarate is a first-generation antihistamine with significant anticholinergic effects; use cautiously in elderly due to risk of confusion, urinary retention, and falls. Avoid in patients with narrow-angle glaucoma, BPH, or severe liver disease. Onset of action is 15-30 minutes, duration 4-6 hours. Sedation is prominent; warn patients about driving or operating machinery. |
| Patient Advice | Take exactly as prescribed; do not exceed recommended dose. · May cause drowsiness or dizziness; avoid driving or heavy machinery until you know how you react. · Avoid alcohol; it can increase drowsiness and side effects. · Do not use with other antihistamines or cold medications without consulting your doctor. · If you have difficulty urinating, vision problems, or glaucoma, talk to your doctor before use. · Store at room temperature away from moisture and heat. |