Phenergan

Phenergan is treating different types of allergy symptoms, including itching, runny nose, sneezing, itchy or watery eyes, hives, and itchy skin rashes.

Product dosage: 25mg
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Synonyms Allersoothe Anergan Antiallersin Anvomin Atosil Avomine Closin Diphergan Diprazinum Fargan Farganesse Fenazil Fenazin Fenazine Fenergan Frinova Hiberna Histabil Histaloc Histantil Histazin Histerzin Insomn-eze Lenazine Lergigan Lilly Nufapreg Otosil Pamergan Phenadoz Phenerex Phenerzine Phergan Pipolphen Polfergan Proazamine chloride Procodin Prohist Promacot Promadryl Promargan Promergan Prometazina Promethacon Promethazin Promethazinum Promethegan Promezin Promodin Proneurin Prorex Prothazin Prothazine Prothiazine Prozin Psicosoma Pyrethia Receptozine Romergan Shogan Synvomin Titanox Tixylix Tixylix linctus V-gan Vegetamin a

Phenergan (promethazine hydrochloride) is a first-generation antihistamine and phenothiazine derivative with established efficacy in managing severe allergic reactions, nausea, vomiting, motion sickness, and as a sedative adjunct. With potent H1-receptor antagonism and central antidopaminergic activity, it provides multi-mechanistic relief for acute and chronic conditions where conventional antihistamines prove insufficient. Its extensive clinical history, rapid onset of action, and flexible administration routes (oral, rectal, injectable) make it a cornerstone in emergency, perioperative, and long-term therapeutic protocols. However, its use requires strict adherence to dosing guidelines and contraindication screening due to potential CNS and respiratory depressant effects.

Features

• Active ingredient: Promethazine hydrochloride (5 mg, 10 mg, 25 mg tablets; 12.5 mg/5mL syrup; 25 mg/mL injection; 12.5 mg/25 mg suppositories)
• Pharmacological class: Phenothiazine-derivative antihistamine
• Onset of action: Oral—20 minutes; IV/IM—3–5 minutes
• Duration of effect: 4–6 hours (up to 12 hours for sedation)
• Administration routes: Oral, intravenous, intramuscular, rectal
• Half-life: 9–16 hours (prolonged in hepatic impairment)

Benefits

• Provides rapid, potent relief from severe allergic reactions including anaphylaxis adjunct therapy
• Effectively controls refractory nausea and vomiting post-operatively or in chemotherapy
• Reduces motion sickness symptoms with prolonged protective effect
• Induces sedation for agitated states or preoperative anxiolysis
• Demonstrates antiemetic and antihistaminic effects at lower doses than many alternatives
• Offers flexible formulation options for patients with swallowing difficulties or NPO status

Common use

Phenergan is indicated for: management of allergic conditions unresponsive to conventional antihistamines; prevention and treatment of nausea/vomis associated with anesthesia, surgery, chemotherapy, or motion sickness; sedation in adults; adjunctive therapy with analgesics for postoperative pain. Off-label uses include management of migraine-associated nausea, treatment of insomnia in specific populations, and as an antiemetic in hyperemesis gravidarum (with extreme caution).

Dosage and direction

Adults:

• Allergies: 25 mg orally at bedtime; may increase to 12.5 mg before meals and 25 mg at bedtime if needed
• Nausea/vomiting: 12.5–25 mg every 4–6 hours orally/IM/IV/rectally
• Motion sickness: 25 mg orally 30–60 minutes before travel, repeat 8–12 hourly if needed
• Sedation: 25–50 mg orally/IM/IV at bedtime or preoperatively

Children (≥2 years):

• Allergies/nausea: 0.25–0.5 mg/kg/dose (max 25 mg) every 4–6 hours orally/IM/rectally
• Motion sickness: 0.5 mg/kg orally (max 25 mg) 30–60 minutes pre-travel

Note: Avoid IV administration in concentrations >25 mg/mL or at rates >25 mg/min. Deep IM injection preferred over subcutaneous to minimize tissue irritation. Do not administer intra-arterially.

Precautions

• CNS depression: Potentiates effects of opioids, sedatives, alcohol. Avoid activities requiring alertness.
• Respiratory depression: Risk increased in children <2 years, elderly, COPD, sleep apnea patients
• Tissue injury: IV extravasation may cause severe chemical irritation, gangrene. Use large veins; avoid repeated injections.
• Seizure threshold: May lower seizure threshold; use caution in epilepsy history
• Bone marrow suppression: Rare agranulocytosis; monitor CBC with prolonged use
• Anticholinergic effects: May exacerbate glaucoma, urinary retention, GI obstruction
• Hepatic/renal impairment: Requires dose reduction; avoid in severe failure
• Pregnancy: Category C; use only if potential benefit justifies fetal risk

Contraindications

• Known hypersensitivity to promethazine or phenothiazines
• Children <2 years due to fatal respiratory depression risk
• Comatose states, CNS depression from alcohol/barbiturates/opioids
• Intra-arterial administration (risk of arterospasm, gangrene)
• Concurrent MAOI therapy (risk of hypertensive crisis)
• Neonates (may potentiate respiratory depression)

Possible side effect

• Common (≥1%): Sedation, dizziness, dry mouth, blurred vision, nausea, vomiting
• Serious: Respiratory depression, neuroleptic malignant syndrome, torsades de pointes, agranulocytosis, severe tissue injury with IV extravasation, seizures
• Pediatric-specific: Paradoxical excitation, apnea, sudden infant death syndrome (in <2 years)
• Dermatological: Photosensitivity, rash, urticaria
• Cardiovascular: Tachycardia, hypotension, syncope

Drug interaction

• CNS depressants: Opioids, benzodiazepines, barbiturates, alcohol—additive sedation/respiratory depression
• MAOIs: Risk of hypertensive crisis, hyperpyrexia
• Anticholinergics: Enhanced dry mouth, urinary retention, ileus
• Epinephrine: Reversed pressor effect (use norepinephrine instead)
• QT-prolonging agents: Increased arrhythmia risk (antiarrhythmics, macrolides, antipsychotics)
• Hepatic enzyme inducers: Rifampin, carbamazepine—reduced promethazine efficacy

Missed dose

If a scheduled dose is missed, administer as soon as remembered unless near next dose time. Do not double dose. For PRN use (e.g., motion sickness), take at first onset of symptoms.

Overdose

Symptoms: Severe CNS depression (coma, respiratory arrest), hypotension, tachycardia, agitation, dystonia, seizures.
Treatment: Supportive care with airway protection, activated charcoal if recent ingestion, IV fluids for hypotension. Avoid stimulants (may induce seizures). Hemodialysis not effective. Contact poison control (1-800-222-1222).

Storage

Store at 20–25°C (68–77°F). Protect from light. Keep oral solution tightly closed. Do not freeze. Keep all formulations out of reach of children. Discard unused injection vials after initial use.

Disclaimer

This information is for educational purposes and does not replace professional medical advice. Phenergan is a prescription medication requiring individualized dosing and supervision. Always consult a healthcare provider for diagnosis, treatment decisions, and adverse event management. Use strictly as prescribed.

Reviews

“Phenergan remains invaluable in our ER for acute allergic presentations where diphenhydramine fails. Its IV formulation provides rapid control of urticaria and angioedema, though we strictly monitor respiratory status.” — Emergency Physician, 12 years experience
“As an oncologist, I reserve Phenergan for breakthrough CINV when 5-HT3 antagonists are insufficient. Effective, but sedation can limit ambulatory use.” — Oncologist, academic medical center
“Used cautiously in postoperative settings, its sedative and antiemetic properties reduce opioid requirements. Avoid in elderly with cognitive impairment.” — Anesthesiologist
“Parental reports indicate excellent motion sickness prevention during long travel, though drowsiness requires planning.” — Pediatric travel medicine specialist