Promethazine

Promethazine

Drug monograph · NCLEX study reference
Trade names	Phenergan
Therapeutic class	Antiemetic, antihistamine, sedative
Pharmacologic class	Phenothiazine (H1 blocker)
Onset / peak / duration	Onset within 20 minutes; duration 4 to 6 hours.
Half-life / level	Half-life 9 to 16 hours; no routine level.
Routes	PO (oral), IV, IM, Rectal
High-alert (ISMP)	No
Black box warning	Yes (see Safety)
Antidote / reversal	Supportive care.
Pregnancy / lactation	Used with caution when needed.

Nursing pharmacology study reference (NCLEX-style monograph). Numeric values are standard teaching ranges for study and must be verified against current manufacturer labeling before clinical use. This is educational content, not prescribing guidance.

Promethazine (brand name Phenergan) — Antiemetic, antihistamine, sedative; Phenothiazine (H1 blocker).

Identification

• Therapeutic class: Antiemetic, antihistamine, sedative.
• Pharmacologic class: Phenothiazine (H1 blocker).

Pharmacology

• Mechanism of action: Blocks H1 and dopamine receptors to reduce nausea and provide sedation.
• Onset / peak / duration: Onset within 20 minutes; duration 4 to 6 hours.
• Half-life / therapeutic level: Half-life 9 to 16 hours; no routine level.

Clinical use

• Indications: Nausea and vomiting, motion sickness, sedation, allergic reactions.
• Usual dose, route, frequency: 12.5 to 25 mg PO, IM, IV, or rectally every 4 to 6 hours.
• Maximum dose / adjustments: Dilute and give IV slowly through a running line; avoid in young children.

Safety

• Contraindications: Children under 2, comatose states, intra-arterial or subcutaneous injection.
• Black box warning: Severe respiratory depression and death in children under 2; severe tissue injury, including gangrene, with IV use or inadvertent arterial or subcutaneous administration.
• Interactions: Central nervous system depressants (additive sedation), anticholinergics, alcohol (food/drink).
• Pregnancy / lactation: Used with caution when needed.
• High-alert: No.

Adverse effects

• Common side effects: Sedation, dry mouth, dizziness.
• Serious effects to report: Respiratory depression, severe injection-site injury, extrapyramidal symptoms.
• Antidote / reversal: Supportive care.

Nursing process

• Assessment before administration: IV line patency, age, respiratory status.
• Interventions during therapy: Give IV diluted and slowly into a large patent vein; never give to young children.
• Monitor: Respiratory rate, sedation, injection site.
• Evaluation / expected outcome: Reduced nausea.

Patient teaching

• Patient teaching: Causes drowsiness; avoid driving and alcohol.
• Notify provider if: Severe burning at the IV site, difficulty breathing.
• Administration tips: IV deeply diluted and slow; preferred IM over IV when possible.