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 |
| Molecular Weight | 406.6 |
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 | Avoid use. Decapryn (doxylamine succinate) is generally avoided in the first trimester unless clearly needed. Antihistamines have been associated with a small increased risk of congenital malformations, although doxylamine has a relatively good safety profile when used for nausea and vomiting of pregnancy. |
| 2nd trimester | Use with caution. Doxylamine is used for nausea and vomiting in pregnancy, particularly as part of the combination product Diclegis (doxylamine/pyridoxine), which is FDA-approved for this indication. However, its use should be limited to cases where benefit outweighs risk. |
| 3rd trimester | Use with caution near term. Avoid high doses in late third trimester as antihistamines may cause uterine contractions, and neonatal withdrawal symptoms (tremors, irritability) have been reported with chronic high-dose use. |
Clinical note
Comprehensive clinical and safety monograph for DECAPRYN (DECAPRYN).
| Placental transfer | Doxylamine crosses the placenta, as evidenced by its use in pregnancy for nausea and vomiting. The degree of transfer is not precisely quantified, but it is likely moderate given its molecular weight and lipophilic nature. |
■ FDA Black Box Warning
Not applicable; no FDA black box warning exists for doxylamine.
| Serious Effects |
Hypersensitivity to doxylamine or any component of the formulationNarrow-angle glaucomaBladder neck obstructionProstatic hypertrophyConcurrent use with monoamine oxidase inhibitors (MAOIs) within 14 days
| 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. |
| Food/Dietary | Avoid alcohol and grapefruit juice; alcohol potentiates sedation, grapefruit juice may alter metabolism. Take on an empty stomach for faster onset, though food does not significantly affect absorption. |
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| Breastfeeding | Doxylamine is excreted into breast milk in small amounts, but data on safety in breastfeeding infants are limited. Due to the potential for sedation in the infant and the presence of anticholinergic effects, it is best to use the lowest effective dose for the shortest duration. Alternatively, consider non-sedating antihistamines if needed. Monitor the infant for drowsiness, irritability, or feeding difficulties. |
| Lactation Rating | L3 (Moderately Safe) |
| 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 | 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. |
| Clinical Pearls | Decapryn (doxylamine succinate) is a first-generation antihistamine with strong sedative effects, used primarily for short-term treatment of insomnia. Avoid in patients with narrow-angle glaucoma, prostatic hypertrophy, or urinary retention. Onset of sedation is about 30 minutes; take 30 minutes before bedtime. Anticholinergic effects may cause dry mouth, constipation, and blurred vision. Use with caution in elderly due to increased risk of falls and confusion. Not recommended for children under 12 years. |
| Patient Advice | Take 30 minutes before bedtime for insomnia; do not exceed recommended dose. · Do not drive or operate machinery after taking this medication until you know how it affects you. · Avoid alcohol and other sedatives as they increase drowsiness. · Report severe drowsiness, confusion, or difficulty urinating to your doctor. · May cause dry mouth; suck on hard candy or chew gum for relief. · Do not use for more than 2 weeks without consulting a doctor. · Keep out of reach of children; overdose may cause hallucinations, seizures, or death. |