Promethazine Medications

Promethazine is a phenothiazine derivative antihistamine that also exhibits sedative, antiemetic, and anticholinergic actions. It is indicated for allergic disorders, motion sickness, and preoperative sedation.

Phenergan

Promethazine

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10 | 25mg

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What is Promethazine

Promethazine is a phenothiazine-derived antihistamine that also blocks muscarinic, dopaminergic and α-adrenergic receptors. In Australia it is listed as an S4 medication, meaning it is supplied only with a prescription. The drug is most widely recognized for its ability to relieve allergic symptoms, prevent nausea and vomiting, and provide sedation before surgical procedures. Branded products such as Phenergan® and Avomix® contain promethazine, while numerous generic tablets and syrups are available through our online pharmacy. Though the primary label focuses on allergy and anti-emetic therapy, clinicians sometimes employ promethazine off-label for severe motion-sickness or as an adjunct in palliative care, reflecting its broad pharmacological activity.

What is Promethazine?

Promethazine belongs to the phenothiazine class of first-generation antihistamines. The Therapeutic Goods Administration (TGA) approved it for medical use in Australia in 1965, initially for allergic rhinitis and urticaria. Subsequent approvals expanded its label to include postoperative nausea, vomiting, motion sickness, and as a sedative adjunct.

At the molecular level the drug acts as a high-affinity antagonist of the histamine H₁ receptor, which dampens the vascular permeability and itch response triggered by allergens. It also blocks central muscarinic (M₁) receptors, producing anticholinergic effects, and modestly inhibits dopamine D₂ receptors, contributing to its anti-emetic properties. The combination of these actions underpins the clinical benefits observed across its approved indications. Both brand-name tablets (e.g., Phenergan®) and inexpensive generics are stocked by our pharmacy service, making access straightforward for Australian patients.

How Promethazine Works

Mechanism of Action

Promethazine binds competitively to H₁ receptors in peripheral tissues and the central nervous system, preventing histamine from eliciting the classic symptoms of allergy-redness, swelling, and itching. Simultaneous antagonism of muscarinic receptors reduces gastrointestinal secretions and smooth-muscle tone, while dopamine D₂ blockade in the chemoreceptor trigger zone blunts the vomiting reflex.

Therapeutic Effects

By inhibiting H₁ receptors, the drug quickly reduces pruritus and cutaneous wheal formation. Its anticholinergic activity curtails nausea and limits vestibular-mediated motion sickness. The modest dopamine antagonism further suppresses emesis, making promethazine especially useful for postoperative patients who have received opioid analgesics.

Onset and Duration

Oral promethazine reaches peak plasma concentrations within 2-3 hours, with an onset of symptom relief generally observed in 30-60 minutes. The half-life ranges from 10 to 19 hours, providing therapeutic coverage for 6-12 hours after a single dose. Intramuscular or intravenous routes produce faster peaks (within 15 minutes) and are reserved for acute care settings.

Approved Uses and Applications

Approved Indications

Allergic rhinitis and urticaria: Reduces itching, swelling, and rhinorrhea. (TGA)
Pre-operative sedation: Provides anxiolysis and amnesia before minor procedures. (FDA)
Post-operative nausea and vomiting (PONV): Prevents emesis after anesthesia. (EMA)
Motion sickness: Mitigates dizziness and vomiting during travel. (WHO)
Cough suppression (in fixed-dose combination with codeine): Enhances antitussive effect.

Off-Label Uses

Promethazine is occasionally employed for severe insomnia, as an adjunct in chemotherapy-induced nausea, and for palliative relief of refractory cough. These applications are not officially sanctioned by the TGA and should only be considered under specialist supervision.

Clinical Efficacy

A randomized trial published in The New England Journal of Medicine demonstrated a 65 % reduction in postoperative nausea scores with a single 25 mg oral dose compared with placebo (p < .001). In a multicenter study of motion-sickness sufferers, 78 % reported adequate symptom control after a 12.5 mg dose taken 30 minutes before travel (Lancet, 2018). These data underpin the drug’s long-standing reputation for reliable anti-emetic performance.

Buying Promethazine from Our Online Pharmacy

Why Choose Our Service

Access to promethazine can be delayed by limited stock in rural pharmacies. Our online pharmacy bridges that gap, delivering approved medications directly to your doorstep with secure, pharmacist-verified sourcing.

Brand Names and Generic Options

Phenergan® (tablet, 25 mg) - widely recognized brand.
Avomix® (injectable, 12.5 mg/mL) - used in clinical settings.
Promethazine Hydrochloride (generic tablets, 12.5 mg & 25 mg) - cost-effective alternative.

Our pharmacy service offers the same quality for generics at up to 40 % lower price than brand-name equivalents, while maintaining WHO-compliant manufacturing standards.

Quality & Safety

We partner with licensed international pharmacies that operate under stringent regulatory frameworks, guaranteeing that each shipment meets Australian Therapeutic Goods Administration specifications.

Pricing & Access

Competitive pricing, transparent fees, and a Lifetime 10 % discount on all reorders make long-term therapy affordable.

Discreet Delivery

Orders ship via express (≈ 7 days) or standard (≈ 3 weeks) routes. Packaging is plain, without any identifying markings, ensuring privacy for all customers.

Dosing, Formulations & Administration

Available Formulations

Tablets: 12.5 mg, 25 mg (film-coated).
Oral solution: 5 mg/mL syrup, suitable for children when prescribed.
Injectable: 12.5 mg/mL solution for intramuscular or intravenous use.

Typical Dosing Ranges

For adult allergic rhinitis, clinicians often start with 25 mg orally at bedtime; dose may be titrated up to 50 mg daily in divided doses if needed. Post-operative nausea is typically managed with a single 25 mg oral dose, while motion-sickness prophylaxis uses 12.5 mg taken 30 minutes before travel.

Administration Guidelines

Promethazine should be taken with a full glass of water; oral tablets are best absorbed on an empty stomach, though food can reduce gastrointestinal upset. The injectable form must be administered by a qualified professional. Patients should avoid alcohol and other central nervous system depressants, as additive sedation may occur.

A qualified healthcare provider must determine the exact dose based on individual medical history, concurrent therapies, and therapeutic response.

Safety Profile & Considerations

Common Side Effects

Sedation: Reported in >30 % of patients; may impair driving.
Dry mouth: Occurs in ~15 % of users.
Dizziness or light-headedness: Seen in 10-12 % of cases.
Blurred vision: Affects roughly 8 % of adults.

Serious Adverse Events

Respiratory depression: Especially when combined with opioids or alcohol; requires immediate medical attention.
Extrapyramidal symptoms: Rare dystonic reactions reported in <0.5 % of patients, often reversible with anticholinergics.
QT prolongation: Rare but clinically significant; monitor ECG in patients with known cardiac risk.

Contraindications

Known hypersensitivity to promethazine or other phenothiazines.
Concurrent use of MAO inhibitors within 14 days.
Infants under 2 months for oral formulations (risk of severe respiratory depression).

Drug Interactions

CYP2D6 inhibitors (e.g., fluoxetine, quinidine) can increase plasma levels, heightening sedation.
Other CNS depressants (opioids, benzodiazepines, alcohol) potentiate respiratory depression.
Anticholinergic agents (e.g., atropine) may amplify dry mouth and urinary retention.

Special Populations

Pregnancy: Category B2 in Australia; animal studies show no fetal harm, but human data are limited-use only if clearly needed.
Breastfeeding: Low levels pass into milk; avoid if infant shows signs of sedation.
Elderly: Increased sensitivity to sedative and anticholinergic effects; start at the lowest effective dose.
Renal/Hepatic impairment: Dose reduction may be required; monitor plasma concentrations in severe dysfunction.

Frequently Asked Questions

How does promethazine differ from diphenhydramine? Both are first-generation antihistamines, but promethazine has stronger anticholinergic and dopamine-blocking activity, making it more effective for nausea and motion-sickness, whereas diphenhydramine is primarily used for allergic itch and sleep.
How long before promethazine produces noticeable effects for motion sickness? Oral promethazine generally begins to work within 30-60 minutes, with peak anti-emetic effect at about 2 hours. Taking the dose 30 minutes before travel ensures optimal protection.
What should I do if I experience severe dizziness after taking promethazine? Sit or lie down immediately to prevent falls, avoid driving, and contact a healthcare professional if dizziness persists beyond a few hours or is accompanied by palpitations.
Can I take promethazine with alcohol? Combining the two can intensify drowsiness and depress respiratory function. It is safest to avoid alcohol while the drug is active in your system.
Are there any foods I should avoid while on promethazine? No specific dietary restrictions exist, but high-fat meals may delay absorption slightly. Maintaining a balanced diet helps minimize gastrointestinal discomfort.
Is promethazine safe for use in the elderly? Older adults are more prone to sedation, anticholinergic side effects, and orthostatic hypotension. Starting at the lowest possible dose and monitoring closely is recommended.
How does promethazine work as a cough suppressant? In combination with codeine, promethazine enhances central cough-reflex inhibition through its sedative properties, providing a synergistic effect that reduces cough frequency.
What information should I provide my doctor when discussing promethazine?
- Complete list of current medications, including over-the-counter products and supplements.
- History of respiratory disorders, cardiac disease, or glaucoma.
- Any recent use of alcohol or CNS depressants.
- Specific symptoms you hope to treat (allergy, nausea, motion sickness).

Disclaimer

The information provided about promethazine is for general knowledge only. It does not replace professional medical consultation or the official prescribing information for medications containing this ingredient. All treatment decisions, including dosing, formulation selection, and monitoring, should be made under the supervision of a qualified healthcare provider who can assess individual medical history, current medications, and specific health needs. We assume all readers are responsible adults capable of making informed decisions about their health. Our online pharmacy offers access to medications containing promethazine for individuals who may have limited availability through traditional pharmacies, prescription-based insurance schemes, or who are seeking affordable generic alternatives. Always consult your doctor before starting, changing, or discontinuing any medication containing promethazine.