CARBINOXAMINE MALEATE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for CARBINOXAMINE MALEATE (CARBINOXAMINE MALEATE).
Carbinoxamine maleate is a first-generation antihistamine that competitively inhibits histamine at H1 receptors, thereby preventing histamine-mediated effects such as vasodilation, increased capillary permeability, and bronchoconstriction. It also exhibits anticholinergic and sedative properties.
| Metabolism | Hepatic metabolism primarily via CYP2D6; also undergoes N-demethylation and other oxidative pathways. |
| Excretion | Primarily renal excretion of metabolites and unchanged drug; ~60-70% of a dose is excreted in urine within 48 hours, with less than 5% as unchanged drug. Biliary/fecal elimination accounts for a minor fraction (<10%). |
| Half-life | Terminal elimination half-life is approximately 10-12 hours in healthy adults; may be prolonged in elderly or patients with hepatic impairment, requiring dose adjustment in significant liver disease. |
| Protein binding | Approximately 50-60% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | Volume of distribution is approximately 5-10 L/kg, indicating extensive tissue distribution. This high Vd is due to lipophilicity and uptake into tissues including CNS. |
| Bioavailability | Oral bioavailability is approximately 25-50% due to first-pass metabolism. Food does not significantly affect absorption. |
| Onset of Action | Oral: Onset of antihistaminic effect occurs within 15-30 minutes, with peak effect at 1-2 hours. Topical: Not applicable. |
| Duration of Action | Duration of action is 4-6 hours for antihistaminic effect, though sedation may persist longer. Clinical tolerance to sedative effects may develop with continued use. |
Adults: 4-8 mg orally every 6-8 hours as needed. Maximum: 24 mg/day.
| Dosage form | TABLET |
| Renal impairment | GFR 30-50 mL/min: no adjustment. GFR <30 mL/min: increase dosing interval to every 12-24 hours due to risk of accumulation. |
| Liver impairment | Child-Pugh Class A: no adjustment. Child-Pugh Class B or C: reduce dose by 50% or use with caution due to increased risk of CNS effects. |
| Pediatric use | Children 2-6 years: 1-2 mg orally every 6-8 hours (max 6 mg/day). Children 6-12 years: 2-4 mg orally every 6-8 hours (max 12 mg/day). Adolescents >12 years: same as adult dosing. |
| Geriatric use | Initiate at 2 mg orally every 8-12 hours; titrate cautiously due to increased sensitivity, anticholinergic effects, and risk of confusion or falls. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for CARBINOXAMINE MALEATE (CARBINOXAMINE MALEATE).
| Breastfeeding | Carbinoxamine is excreted into breast milk in low amounts (M/P ratio not reported in literature). Infants may experience irritability, drowsiness, or paradoxical CNS stimulation. Avoid use in breastfeeding mothers of premature or neonates due to potential respiratory depression. |
| Teratogenic Risk | First trimester: Limited human data; animal studies show no consistent teratogenicity at clinically relevant doses. Second and third trimesters: Risk of neonatal irritability, tremor, and transient respiratory depression if used near term. Anticholinergic effects may theoretically reduce uterine blood flow; no direct evidence of major malformations. |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to carbinoxamine or any component of the formulation","Premature and full-term neonates due to increased risk of anticholinergic side effects (e.g., severe drowsiness, apnea)","Nursing mothers (excreted in breast milk; may cause drowsiness or irritability in infants)","Concurrent use with monoamine oxidase inhibitors (MAOIs) due to risk of hypertensive crisis and prolonged anticholinergic effects"]
| Precautions | ["May cause marked drowsiness and impair cognitive/motor performance; caution when driving or operating machinery.","Avoid concurrent use with CNS depressants (e.g., alcohol, sedatives, tranquilizers).","Use with caution in patients with asthma, COPD, increased intraocular pressure, glaucoma, prostatic hyperplasia, urinary retention, cardiovascular disease, hypertension, hyperthyroidism, or seizure disorders.","Elderly patients are more sensitive to anticholinergic effects (e.g., dizziness, sedation, hypotension).","May cause excitation in children, especially with overdosage."] |
| Food/Dietary |
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| Fetal Monitoring | Monitor fetal heart rate and uterine activity if used intravenously or in high doses. Assess neonatal Apgar scores and vigilance for transient CNS depression or anticholinergic effects postpartum. |
| Fertility Effects | No evidence of adverse effects on human fertility; animal studies show no impairment of fertility at therapeutic doses. |
| No significant food interactions. However, alcohol should be avoided due to additive CNS depression. Grapefruit juice may alter metabolism; avoid excessive consumption. |
| Clinical Pearls | Carbinoxamine maleate is a first-generation antihistamine with significant sedative properties. It is often used in combination products for allergy or cold symptoms. Avoid in patients with asthma, narrow-angle glaucoma, prostatic hypertrophy, or urinary retention. It can cause paradoxical excitation in children. Onset of action is about 15-30 minutes, duration 4-6 hours. Monitor for anticholinergic effects (dry mouth, blurred vision, constipation). |
| Patient Advice | Take only as directed; do not exceed recommended dose. · Avoid driving or operating heavy machinery as this medication causes drowsiness. · Do not combine with alcohol or other CNS depressants (sleeping pills, tranquilizers). · Notify your doctor if you experience blurred vision, difficulty urinating, or rapid heartbeat. · Store at room temperature, away from moisture and heat. |