PROMETH PLAIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PROMETH PLAIN (PROMETH PLAIN).
Antagonist at histamine H1 receptors; also exhibits anticholinergic, antiemetic, and sedative effects.
| Metabolism | Hepatic metabolism via CYP2D6; metabolites are excreted renally. |
| Excretion | Primarily renal (approximately 70%) as metabolites and unchanged drug; biliary/fecal excretion accounts for ~20%. |
| Half-life | Terminal elimination half-life is 10-14 hours in adults; may be prolonged in elderly or hepatic impairment. |
| Protein binding | Approximately 93% bound primarily to albumin. |
| Volume of Distribution | Approximately 9-12 L/kg, indicating extensive tissue distribution. |
| Bioavailability | Oral: ~25% due to significant first-pass metabolism; IM: 70-85%. |
| Onset of Action | Oral: 30-60 min; IM: 20-30 min; IV: 5-10 min. |
| Duration of Action | 4-6 hours for antihistamine effects; sedative effects may persist longer. |
12.5-25 mg intramuscularly or intravenously every 4-6 hours as needed; maximum 100 mg/day.
| Dosage form | SYRUP |
| Renal impairment | No specific adjustment required; use with caution in severe renal impairment (eGFR <30 mL/min) due to potential accumulation. |
| Liver impairment | Child-Pugh Class A: No adjustment. Child-Pugh Class B: Reduce dose by 50%. Child-Pugh Class C: Avoid use or reduce dose by 75% with careful monitoring. |
| Pediatric use | Weight-based: 0.25-0.5 mg/kg intramuscularly or intravenously every 4-6 hours; maximum 10 mg for children <5 years or 25 mg for children 5-12 years. |
| Geriatric use | Lower initial doses recommended (6.25-12.5 mg) due to increased sensitivity and risk of sedation, hypotension, and anticholinergic effects; maximum 50 mg/day. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PROMETH PLAIN (PROMETH PLAIN).
| Breastfeeding | Promethazine excreted in breast milk; M/P ratio approximately 1.0. Avoid use in breastfeeding due to potential for infant sedation, irritability, and apnea, especially in neonates or at-risk infants. Consider alternative agents. |
| Teratogenic Risk | FDA Pregnancy Category C. First trimester: No adequate studies; animal studies show no teratogenicity, but embryocidal effects at high doses. Second/third trimester: Prolonged use near term may cause extrapyramidal signs or withdrawal in neonate; potential for respiratory depression if used with other CNS depressants. |
■ FDA Black Box Warning
Do not use in children younger than 2 years due to risk of respiratory depression and death; use with caution in children 2 years and older.
| Serious Effects |
["Hypersensitivity to promethazine or any component","Children younger than 2 years","Comatose states","Use of MAO inhibitors"]
| Precautions | ["May cause CNS depression and impair mental alertness","Avoid concurrent use with other CNS depressants","Use with caution in patients with asthma, COPD, or sleep apnea","Risk of extrapyramidal symptoms, especially in children","May cause anticholinergic effects (e.g., dry mouth, urinary retention)"] |
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| Fetal Monitoring |
| Monitor maternal blood pressure, heart rate, and respiratory status; assess for excessive sedation. Fetal monitoring: Nonstress test and biophysical profile in third trimester if chronic use. Neonatal monitoring for extrapyramidal signs, sedation, and respiratory depression after delivery. |
| Fertility Effects | No established effect on human fertility. Animal studies show no impairment of fertility at therapeutic doses. Theoretical risk due to hyperprolactinemia from dopamine antagonism, but clinical significance is minimal. |