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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for CLEMASTINE FUMARATE (CLEMASTINE FUMARATE).
| Breastfeeding | Excreted into breast milk in small amounts; expected infant dose <10% of maternal weight-adjusted dose. M/P ratio not established. Caution advised; monitor infant for drowsiness, irritability, and feeding difficulties. |
| 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. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to clemastine or any component of the formulation.","Concurrent use of MAOIs (potential for severe anticholinergic effect).","Lower respiratory tract symptoms (e.g., asthma) due to anticholinergic effect.","Neonates or premature infants due to increased risk of CNS depression."]
| 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. |
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| 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. |