UNISOM
Clinical safety rating: caution
Comprehensive clinical and safety monograph for UNISOM (UNISOM).
Antihistamine (H1-receptor antagonist); also exhibits anticholinergic and sedative properties.
| Metabolism | Hepatic via CYP450 (CYP2D6, CYP3A4); active metabolite monodesmethyldoxylamine. |
| Excretion | Primarily renal (hepatic metabolism to inactive metabolites, ~30–60% excreted in urine unchanged; small amounts in feces) |
| Half-life | Terminal elimination half-life is approximately 10–12 hours in adults; may be prolonged in elderly or hepatic impairment |
| Protein binding | Approximately 78–80% bound to plasma proteins (primarily albumin) |
| Volume of Distribution | Approximately 2.5–7.5 L/kg (large Vd indicating extensive tissue distribution, including central nervous system) |
| Bioavailability | Oral: approximately 80–90% (due to limited first-pass metabolism) |
| Onset of Action | Oral: 15–60 minutes for sedative effect; maximum effect 2–3 hours post-dose |
| Duration of Action | Sedative effects last 4–6 hours; antihistamine effects may persist up to 8–12 hours |
| Molecular Weight | 388.51 |
25 mg orally once daily at bedtime (doxylamine succinate).
| Dosage form | CAPSULE |
| Renal impairment | GFR < 30 mL/min: avoid use or reduce dose; specific guidelines not established. |
| Liver impairment | Child-Pugh class C: avoid use; class A or B: no specific adjustment but caution due to increased sedation risk. |
| Pediatric use | Weight-based: 1 mg/kg up to 25 mg orally at bedtime for children ≥12 years; children <12 years: not recommended. |
| Geriatric use | Start at 12.5 mg orally at bedtime; monitor for sedation, confusion, anticholinergic effects; avoid if possible due to increased risk of falls. |
| 1st trimester | Limited human data; animal studies not suggestive of risk. Use only if clearly needed. |
| 2nd trimester | Generally considered safe; no known teratogenic effects. |
| 3rd trimester | Avoid near term due to potential antihistamine effects (e.g., respiratory depression in neonates). |
Clinical note
Comprehensive clinical and safety monograph for UNISOM (UNISOM).
| Placental transfer | Doxylamine crosses the placenta. Animal studies show placental transfer. Human data limited. |
| Breastfeeding | Doxylamine is excreted into breast milk in small amounts. Reports of drowsiness and irritability in infants. Use with caution, especially in preterm neonates. Monitor infant for sedation. |
| Lactation Rating |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to doxylamine or any componentConcurrent use with MAO inhibitorsAcute asthma attackNarrow-angle glaucomaUrinary retention (e.g., prostatic hypertrophy)Severe liver diseasePyloroduodenal obstruction
| Precautions | Avoid alcohol and other CNS depressants, Use with caution in asthma, glaucoma, urinary obstruction, and BPH, May cause drowsiness, impair cognitive/motor function, Avoid in premature infants and neonates due to risk of SIDS |
| Food/Dietary | Avoid grapefruit juice as it may increase diphenhydramine absorption. Alcohol potentiates sedation and should be avoided. |
| Clinical Pearls |
Loading safety data…
| L3 (Moderately Safe) |
| Teratogenic Risk | Unisom (doxylamine succinate) is classified as FDA Pregnancy Category A. Large controlled studies and epidemiological data show no increased risk of fetal abnormalities in any trimester. First trimester use is associated with no increased teratogenicity; second and third trimester risks are not increased. No fetal harm has been demonstrated. |
| Fetal Monitoring | No specific fetal monitoring required. Monitor maternal sedation level and anticholinergic effects. Avoid use in third trimester near term due to potential neonatal withdrawal symptoms if used chronically. |
| Fertility Effects | No adverse effects on fertility reported. In animal studies, no impairment of fertility was observed at clinically relevant doses. Human data are lacking but no known negative impact. |
| Unisom Sleep Gels contain diphenhydramine, an antihistamine with sedative properties. Use lowest effective dose to minimize anticholinergic side effects (dry mouth, constipation, confusion). Avoid in elderly due to increased fall risk. Caution in glaucoma, benign prostatic hyperplasia, and respiratory depression. Drug interactions include MAOIs, CNS depressants (alcohol, benzodiazepines). |
| Patient Advice | Take Unisom 30 minutes before bedtime. · Do not exceed recommended dose (50 mg diphenhydramine). · Avoid alcohol and other sedatives while taking Unisom. · May cause drowsiness the next day; do not drive or operate machinery. · Avoid use in children under 12 years old. · Consult doctor if pregnant or breastfeeding. · Stop use and seek medical help if allergic reactions occur. |