DECAPRYN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for DECAPRYN (DECAPRYN).
Decapryn (doxylamine) is a first-generation antihistamine that acts as an inverse agonist at histamine H1 receptors, thereby inhibiting the effects of histamine in the respiratory tract, vascular endothelium, and other tissues. It also has significant anticholinergic and sedative properties through central H1 receptor blockade and muscarinic receptor antagonism.
| Metabolism | Primarily hepatic via N-demethylation and other oxidative pathways; CYP450 enzymes involved but specific isozymes not well characterized. |
| Excretion | Primarily renal (90-95% as metabolites, <5% unchanged); minor fecal (<5%) |
| Half-life | Terminal elimination half-life is approximately 9-10 hours in adults; up to 15 hours in elderly, no significant change in renal impairment |
| Protein binding | Approximately 96-99% bound primarily to albumin |
| Volume of Distribution | Vd ~4.5-5.0 L/kg, indicating extensive tissue distribution |
| Bioavailability | Oral: ~40-60% due to first-pass metabolism; IM: ~70-85% |
| Onset of Action | Oral: 15-30 minutes; intramuscular: 10-15 minutes; intravenous: immediate (within 1-2 minutes) |
| Duration of Action | Duration is 4-6 hours for antihistaminic effects; may be longer up to 12 hours for sedative effects |
25 mg orally every 4 to 6 hours as needed, not to exceed 150 mg per day; or 50 mg intramuscularly every 4 to 6 hours as needed.
| Dosage form | TABLET |
| Renal impairment | GFR 30-50 mL/min: 25 mg every 8 hours; GFR 10-29 mL/min: 25 mg every 12 hours; GFR <10 mL/min: avoid use or use with extreme caution at 25 mg every 24 hours. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: avoid use or use at 25 mg every 12 hours if benefits outweigh risks. |
| Pediatric use | Children 2-6 years: 6.25 mg orally every 4-6 hours (max 37.5 mg/day); 6-12 years: 12.5 mg orally every 4-6 hours (max 75 mg/day); >12 years: adult dosing. Not recommended for infants <2 years. |
| Geriatric use | Initiate at 25 mg orally every 8 hours; increase to every 6 hours if tolerated; monitor for anticholinergic effects, sedation, and falls. Avoid in patients with cognitive impairment or delirium risk. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for DECAPRYN (DECAPRYN).
| Breastfeeding | Excreted in breast milk in small amounts; M/P ratio not established. Monitor infant for irritability, poor feeding, and sedation. Use caution; avoid high doses or prolonged use. |
| Teratogenic Risk | First trimester: Limited human data; animal studies show no consistent teratogenicity. Second/third trimester: Risk of neonatal respiratory depression, irritability, and paradoxical CNS stimulation if used near term. Avoid in late pregnancy due to anticholinergic effects. |
| Fetal Monitoring |
■ FDA Black Box Warning
Not applicable; no FDA black box warning exists for doxylamine.
| Serious Effects |
["Hypersensitivity to doxylamine or any component of the formulation","Concomitant use of monoamine oxidase inhibitors (MAOIs) due to risk of hypertensive crisis","Acute asthma attack","Lower respiratory tract symptoms, including pneumonia or bronchitis"]
| Precautions | ["Avoid use in patients with narrow-angle glaucoma, symptomatic prostatic hypertrophy, urinary retention, or pyloroduodenal obstruction due to anticholinergic effects.","May cause marked drowsiness; patients should avoid driving or operating machinery.","Use with caution in elderly patients due to increased risk of falls, confusion, and anticholinergic side effects.","Not recommended in neonates or premature infants due to risk of respiratory depression."] |
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| Monitor maternal blood pressure, heart rate, and anticholinergic effects. Fetal monitoring for heart rate variability if used near term. Assess neonatal respiratory status and CNS effects post-delivery if used late in pregnancy. |
| Fertility Effects | No direct evidence of impaired fertility in humans. Anticholinergic effects may theoretically affect cervical mucus or implantation; no clinical significance reported. |