BENDECTIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for BENDECTIN (BENDECTIN).
Combination of doxylamine (antihistamine) and pyridoxine (vitamin B6). Doxylamine blocks histamine H1 receptors, reducing nausea and vomiting. Pyridoxine acts as a cofactor in neurotransmitter synthesis, modulating nausea pathways.
| Metabolism | Doxylamine: extensively metabolized in the liver via N-demethylation and other pathways, mainly by CYP450 enzymes. Pyridoxine: metabolized to active forms (pyridoxal phosphate) primarily in the liver. |
| Excretion | Renal: mostly as metabolites. Doxylamine: ~60% as unchanged drug and metabolites; pyridoxine: ~70-80% as metabolites (primarily 4-pyridoxic acid). Fecal: minimal (<10%) for both components. |
| Half-life | Doxylamine: 10-12 hours (range 6-15h) in healthy adults; prolonged in hepatic impairment or elderly. Pyridoxine: 15-20 days (as pyridoxal phosphate in tissues); elimination half-life of pyridoxine per se is 2-3 hours. |
| Protein binding | Doxylamine: ~30-40% bound to plasma proteins (albumin). Pyridoxine: negligible binding. |
| Volume of Distribution | Doxylamine: ~3-4 L/kg (wide distribution, including CNS); pyridoxine: ~0.6 L/kg (predominantly hepatic and muscle storage). |
| Bioavailability | Oral: Doxylamine ~70-90% (first-pass metabolism limited); pyridoxine ~80-90% (extensive conversion to active forms). |
| Onset of Action | Oral: Doxylamine: 30-60 minutes (antihistamine effect); pyridoxine: 1-2 hours (metabolic effect). |
| Duration of Action | Doxylamine: 4-6 hours for sedation; pyridoxine: up to 24 hours for vitamin repletion. Antihistamine effects persist as long as drug is present. |
10 mg doxylamine succinate + 10 mg pyridoxine hydrochloride orally once daily at bedtime, increased to twice daily (one tablet in morning and one at bedtime) and then three times daily (one tablet in morning, one in midafternoon, and one at bedtime) as needed, max 4 tablets per day.
| Dosage form | TABLET, EXTENDED RELEASE |
| Renal impairment | No specific dose adjustment guidelines; contraindicated in severe renal impairment (CrCl <30 mL/min or on dialysis) due to risk of accumulation. |
| Liver impairment | Contraindicated in severe hepatic impairment (Child-Pugh class C). Use with caution in moderate impairment (Child-Pugh class B); consider dose reduction or extended interval, but no formal guidelines. |
| Pediatric use | Not recommended for use in pediatric patients (<18 years) as safety and efficacy not established. |
| Geriatric use | Caution in elderly due to increased sensitivity to anticholinergic effects; consider lower starting dose (e.g., one tablet at bedtime) and monitor for confusion, sedation, falls. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for BENDECTIN (BENDECTIN).
| Breastfeeding | Doxylamine and pyridoxine are excreted into breast milk in small amounts. M/P ratio not well established. Compatible with breastfeeding, but monitor infant for sedation. |
| Teratogenic Risk | Bendectin (doxylamine/pyridoxine) is not associated with increased risk of major malformations in any trimester. No fetal risks identified in cohort studies. |
| Fetal Monitoring |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to doxylamine succinate, pyridoxine hydrochloride, or any inactive ingredient.","Concomitant use with monoamine oxidase inhibitors (MAOIs) may prolong and intensify anticholinergic effects.","Porphyria (due to possible exacerbation)."]
| Precautions | ["Somnolence: may impair mental and/or physical abilities; avoid driving or operating machinery.","CNS depression: concurrent use with alcohol or other CNS depressants may exacerbate.","Anticholinergic effects: caution in patients with asthma, glaucoma, or gastrointestinal obstruction.","Severe skin reactions: rare but possible."] |
| Food/Dietary | Take on an empty stomach with a glass of water for best absorption. Avoid alcohol as it may increase drowsiness and central nervous system depression. No specific food restrictions; however, if vomiting persists, consume small, frequent meals and bland foods. |
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| No specific monitoring required. Standard prenatal care. |
| Fertility Effects | No known effects on fertility. |
| Clinical Pearls | Doxylamine/pyridoxine (Bendectin) is the only FDA-approved treatment for nausea and vomiting of pregnancy (NVP). Use delayed-release formulation to reduce morning sedation. Titrate dose based on symptom timing; if morning nausea predominates, take at bedtime; if afternoon nausea, take in morning and at bedtime. Avoid in patients with asthma, glaucoma, or urinary retention due to anticholinergic effects of doxylamine. |
| Patient Advice | Take this medication exactly as prescribed, usually once or twice daily. · The delayed-release tablet should be swallowed whole; do not crush or chew. · May cause drowsiness; avoid driving or operating heavy machinery until you know how it affects you. · If you miss a dose, skip it; do not double the next dose. · Contact your healthcare provider if symptoms worsen or do not improve after a few days. · This medication is safe for use during pregnancy; do not stop without consulting your doctor. |