Promethazine: Nursing Drug Guide, Respiratory Depression & IV Safety

Promethazine hydrochloride is available generically and as Phenergan (tablets, oral solution, rectal suppositories, and injection). Combination products pair promethazine with dextromethorphan (Promethazine DM), codeine, or phenylephrine—each adds distinct sedation, opioid, or vasoconstrictor risks.

• Single entity: 12.5 mg, 25 mg, and 50 mg tablets; 6.25 mg/5 mL and 25 mg/5 mL oral solutions; 25 mg/mL and 50 mg/mL injection
• Combination alert: Do not stack promethazine syrup with separate sedating antihistamines, opioid cough products, or PRN antiemetics without pharmacy review
• Not interchangeable with: ondansetron or other 5-HT₃ antiemetics—different respiratory and neurologic risk profiles

Promethazine is a phenothiazine-derivative H₁ blocker with clinically useful sedative, antiemetic, and antimotion-sickness effects per U.S. tablet and injection labeling.

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Promethazine blocks H₁ receptors and provides sedative and antiemetic effects. As a phenothiazine derivative with a branched side chain, it has relatively weak dopamine antagonism compared with antipsychotic phenothiazines—but nurses still monitor for extrapyramidal symptoms and neuroleptic malignant syndrome because these remain labeled risks.

Anticholinergic properties contribute to dry mouth, urinary retention, and confusion, especially when combined with other anticholinergic drugs. CNS depressant effects amplify opioids, sedatives, and general anesthetics—respiratory depression is the highest-stakes interaction, particularly in young children and patients with compromised respiration.

Doses below are from current U.S. promethazine tablet/oral solution prescribing information unless noted. Verify product strength, route, and indication on the MAR. Promethazine is contraindicated in children under 2 years.

Pediatrics (≥2 years only)

• Never use in children <2 years—boxed warning for fatal respiratory depression
• Motion sickness: 12.5–25 mg twice daily (tablets/syrup/suppository) per tablet labeling
• Nausea/vomiting: usual dose 0.5 mg/lb body weight, adjusted to age, weight, and severity—repeat q4–6 h
• Sedation: 12.5–25 mg at bedtime (children); use lowest effective dose in ages 2+ and avoid respiratory depressant stacking

Renal and hepatic adjustment

Not specified in the reviewed prescribing information for tablet labeling. Use cautiously with hepatic impairment per precautions. Institutional protocols and product formulations may vary—consult pharmacy for parenteral products.

Missed dose: Give when remembered if not near next scheduled dose; do not double. For PRN antiemetic/sedation orders, reassess indication and respiratory status before giving a late dose.

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Pretreatment checks

• Confirm age ≥2 years—verify date of birth on every pediatric dose; never accept verbal age alone
• Review respiratory status, history of asthma, COPD, or sleep apnea
• Complete medication reconciliation for opioids, benzodiazepines, other sedating antihistamines (diphenhydramine, hydroxyzine), and MAO inhibitors
• For IV/IM: verify route, concentration, patency of IV site, and that subcutaneous route is not ordered
• Baseline mental status, respiratory rate, SpO₂, and blood pressure—especially post-op and pediatric patients
• Screen for phenothiazine or promethazine allergy and prior extrapyramidal reaction

• Pediatric patients <2 years (boxed warning—fatal respiratory depression)
• Comatose states
• Hypersensitivity or idiosyncratic reaction to promethazine or other phenothiazines
• Lower respiratory tract symptoms including asthma (antihistamines contraindicated for asthma treatment per tablet labeling)
• Subcutaneous promethazine injection (injection labeling)
• Intra-arterial injection (injection labeling—gangrene risk)

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Oral and rectal

• May administer with or without food per institutional practice; motion-sickness doses given before travel
• Inspect oral solution for color/particulate matter—product is light sensitive per injection/oral labeling
• Do not exceed labeled frequency; titrate to smallest effective dose especially in pediatrics ≥2 years

Intramuscular (preferred parenteral route)

• Give by deep IM injection per injection labeling—preferred over IV because of tissue injury risk
• Use IM injection technique standards; rotate sites; document volume and site

Intravenous — high-risk route

• Only when IV is required: concentration ≤25 mg/mL, rate ≤25 mg/minute
• Inject through tubing of a functioning IV infusion set; use large veins—avoid hand/wrist when possible
• Stop immediately if patient reports burning or pain—assess for extravasation or intra-arterial placement
• Follow IV bolus administration and institutional promethazine IV policies

• Reduced nausea/vomiting and improved tolerance of oral intake when etiology supports antiemetic use
• Decreased allergic symptoms (rhinitis, pruritus) without excessive sedation in ambulatory patients
• Motion sickness: fewer episodes when prophylactic dose timed before travel
• Controlled apprehension and light sleep for procedural/obstetric sedation with arousability
• Not working / concerning: persistent vomiting of unknown cause in a child, worsening somnolence, falling respiratory rate, paradoxical agitation, or new involuntary movements—hold and reassess

• Respiratory rate decline, apnea, or difficult arousal—especially in toddlers or post-op patients receiving opioids
• IV injection site burning, swelling, pallor, or severe pain—stop infusion/injection and escalate per extravasation protocol
• Acute dystonia: torticollis, oculogyric crisis, tongue protrusion—hold drug; diphenhydramine or anticholinergic antiparkinsonian agents may be ordered per labeling
• High fever, rigid muscles, altered mental status, autonomic instability—suspect neuroleptic malignant syndrome
• Paradoxical hyperexcitability, nightmares, or agitation (more common in children)
• Severe hypotension or syncope—do not treat with epinephrine per labeling
• Signs of agranulocytosis or severe hematologic reaction when on other marrow-toxic drugs
• Jaundice or cholestatic symptoms—promethazine associated with cholestatic jaundice per labeling

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Overdose may range from mild CNS depression to profound hypotension, respiratory depression, unconsciousness, and sudden death per labeling. Children may show paradoxical stimulation; atropine-like signs (dry mouth, dilated pupils) may occur.

Management (per labeling)

• No specific antidote—supportive care; promethazine depression is not reversed by naloxone
• Airway protection and assisted ventilation as needed
• Hypotension: IV fluids first; if vasopressors needed use norepinephrine or phenylephrine—not epinephrine
• Extrapyramidal reactions: diphenhydramine, anticholinergic antiparkinsonian agents, or barbiturates per prescriber
• Convulsions: diazepam may be used per labeling; avoid analeptics that may cause convulsions
• Dialysis not helpful per tablet labeling

• Phenergan vs Phenazopyridine, fentanyl, or similar names—read label aloud; scan barcode when available
• Promethazine vs promethazine/codeine or Promethazine DM—verify single vs combination product every time
• mg vs mL for injection—25 mg/mL and 50 mg/mL concentrations; double-check total milligrams
• Route errors—never give subcutaneous promethazine; question IV orders that bypass institutional IV restrictions
• Pediatric age verification—do not rely on “child” labels; confirm DOB before every dose

↔On a small screen, swipe or scroll sideways to see the full table.

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Monitor

• Respiratory rate, SpO₂, and level of sedation—especially first hour after PO/IM/IV dose
• Mental status, confusion, and dizziness (fall risk)
• IV site before, during, and after injection for pain, swelling, or color change
• Extrapyramidal signs: face, tongue, neck, extremities
• Blood pressure and heart rate—especially with concurrent antihypertensives or dehydration
• Antiemetic effectiveness and hydration status using pain/nausea assessment scales

Document

• Patient age verified, indication, dose, route, time, and response
• Pre-dose respiratory baseline and post-dose reassessment times
• IV: concentration, rate, vein site, patient tolerance, and any interruption for pain
• Hold events, prescriber/pharmacy notifications, and patient/caregiver teaching on respiratory red flags

• This medicine causes drowsiness—do not drive or operate machinery until you know how you respond; avoid alcohol and other sedatives unless prescriber approves
• Caregivers of young children: watch for slow or irregular breathing, difficult arousal, or blue lips—seek emergency care per local guidance
• Report burning pain during any injection immediately
• Report involuntary muscle movements, neck stiffness, high fever with muscle rigidity, or severe restlessness urgently
• For motion sickness, take the first dose 30–60 minutes before travel as directed; avoid duplicate OTC sedating cold products
• Protect skin from sun—photosensitivity reported; use sunscreen and protective clothing
• Do not give leftover promethazine to other children—age and weight matter; products are not interchangeable

Hold parameters may vary by institutional protocol. Follow prescriber orders, pharmacy guidance, and facility policy.

Rehearse NCLEX-style clinical judgment practice for promethazine using a tabbed pediatric postoperative case (MAR, labs, vitals, nursing notes), then priority action, cue recognition, trend interpretation, matrix urgency, clinical judgment, and documentation cloze—recognise respiratory and IV-risk cues → analyse sedative stacking → prioritise holds → act → evaluate outcomes.

This medication guide is written and reviewed using NurseOnShift editorial and clinical review standards.

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• Medical Review Process
• Disclaimer

Educational use only. This content does not replace clinical judgment, prescriber orders, pharmacist guidance, product labeling, or institutional protocols.