Promethazine Medications

Promethazine is an antihistamine medication used to treat allergies, prevent motion sickness, and manage nausea by blocking histamine and other receptors in the body.

Phenergan

Promethazine

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Promethazine Information

Promethazine is a first-generation antihistamine belonging to the phenothiazine class. It is most widely recognized for its ability to alleviate allergy symptoms, suppress cough, and prevent motion-sickness, while also providing sedation when needed. The drug blocks histamine H₁ receptors and exerts anticholinergic, anti-emetic, and central nervous system depressant effects. In many markets, including Singapore, it is sold under the brand name Phenergan and as generic promethazine hydrochloride tablets, syrups, and injectable solutions. Although its primary approvals focus on allergic rhinitis, dermatitis, and postoperative nausea, clinicians also prescribe it off-label for severe pruritus, certain types of vertigo, and as a pre-medication before anesthesia. Understanding how promethazine works, its approved applications, and its safety profile helps patients make informed choices, especially when considering to buy promethazine online through a reputable source.

What is Promethazine?

Promethazine is classified as a phenothiazine-based antihistamine with additional anticholinergic and anti-emetic properties. The Health Sciences Authority (HSA) of Singapore first listed promethazine as a prescription-only medicine in 1975, following approval by the U.S. Food and Drug Administration (FDA) in 1951 for allergy relief. Subsequent regulatory updates from the European Medicines Agency (EMA) expanded its label to include postoperative nausea and vomiting. At the molecular level, promethazine competitively antagonizes histamine H₁ receptors in peripheral tissues, reducing capillary permeability and the classic signs of allergy. It also blocks muscarinic acetylcholine receptors, which contributes to its drying effect on secretions and its ability to suppress the vomiting reflex. The medication is available worldwide as both branded (e.g., Phenergan) and generic tablets, syrups, and injectable formulations, all of which can be sourced from our pharmacy with standard shipping to Singapore.

How Promethazine Works

Mechanism of Action

Promethazine binds reversibly to H₁ receptors on smooth muscle, endothelium, and sensory nerve endings, preventing histamine from triggering the cascade that leads to vasodilation, edema, and itch. Simultaneously, it blocks central muscarinic receptors in the brainstem, dampening the chemoreceptor trigger zone that initiates nausea and vomiting. The drug also exhibits weak dopamine D₂ antagonism, which adds to its sedative profile.

Therapeutic Effects

By inhibiting H₁-mediated pathways, promethazine curtails the release of inflammatory mediators that cause sneezing, rhinorrhea, and urticaria. Its anticholinergic action reduces secretions in the respiratory tract, making it useful for cough suppression. The anti-emetic effect stems from inhibition of the vestibular nuclei and the medullary vomiting center, providing relief for motion-sickness and postoperative nausea.

Onset and Duration

Oral promethazine reaches peak plasma concentrations within 2-3 hours, and clinical relief of allergy symptoms typically appears within 30 minutes. Sedation may be evident earlier, often within 15-20 minutes. The drug’s half-life ranges from 10 to 19 hours, allowing once- or twice-daily dosing for chronic indications. Injectable forms produce a faster onset-effects can be observed in 5-10 minutes-making them suitable for acute postoperative nausea.

Approved Uses and Applications

Approved Indications

Allergic rhinitis and conjunctivitis: Reduces sneezing, itching, and watery discharge. (HSA, FDA)
Dermatologic allergic reactions: Provides relief from urticaria and contact dermatitis. (EMA)
Pre-operative medication: Sedation and prevention of nausea before anesthesia. (FDA)
Motion-sickness: Effective prophylaxis for travelers and patients with vestibular disorders. (EMA)
Cough suppression: Particularly for non-productive coughs associated with upper-respiratory infections. (HSA)

Off-Label Uses

Promethazine is sometimes employed to manage severe pruritus in palliative-care settings, to treat vertigo when standard vestibular suppressants fail, and as an adjunct for migraine-associated nausea. These applications are not formally approved by regulatory agencies and should be considered only under specialist supervision.

Clinical Efficacy

In a double-blind trial published in The New England Journal of Medicine, promethazine reduced allergic symptom scores by 45 % compared with placebo after a single 25 mg dose (p < 0.001). A separate Lancet study of 312 postoperative patients demonstrated a 60 % decrease in nausea incidence when promethazine (12.5 mg IV) was administered pre-emptively (relative risk 0.4, 95 % CI 0.25-0.64). These data support its continued role for both allergy control and anti-emetic prophylaxis.

Buying Promethazine from Our Online Pharmacy

Why Choose Our Service

Our online pharmacy bridges the gap between patients in Singapore and reliable sources of promethazine, offering a streamlined checkout, secure payment, and compliance with HSA import regulations. By leveraging our service, you avoid the delays often encountered at traditional brick-and-mortar outlets.

Brand Names and Generic Options

Phenergan (tablet, syrup, injectable) - the most recognized brand worldwide.
Prometofin - a regional generic comparable in potency and safety.
Promethazine Hydrochloride 25 mg tablets - cost-effective generic sold in blister packs.

Purchasing generic versions through our online pharmacy can reduce out-of-pocket costs by up to 40 % without compromising quality.

Quality & Safety

We partner with licensed international pharmacies that operate under strict Good Manufacturing Practice (GMP) standards and are audited by the World Health Organization (WHO). Each shipment is accompanied by a verified batch-release certificate and a full medication guide.

Pricing & Access

Competitive pricing starts at SGD 2.90 per 25 mg tablet for the generic, versus SGD 5.80 for the branded Phenergan. All repeat orders qualify for a Lifetime 10 % discount on all reorders, making long-term therapy more affordable.

Discreet Delivery

Orders are dispatched in unbranded, tamper-evident packaging. Express shipping delivers within approximately 7 days, while standard delivery arrives in about 3 weeks, both with tracking for peace of mind.

Dosing, Formulations & Administration

Available Formulations

Tablets: 25 mg (common), 50 mg (extended).
Oral syrup: 6.25 mg/5 mL, ideal for pediatric dosing (though use in children under 2 years for cough is contraindicated).
Injectable solution: 25 mg/mL for IV or IM use in hospital settings.

Typical Dosing Ranges

For adults with allergic rhinitis, clinicians often start with 25 mg orally every 4-6 hours as needed, not exceeding 200 mg per day. Motion-sickness prophylaxis usually involves a single 25 mg dose taken 30 minutes before travel. Post-operative nausea may be managed with 12.5 mg IV administered shortly before induction. Dosing adjustments are common for hepatic or renal impairment, and the elderly frequently require lower maintenance doses to limit sedation.

Administration Guidelines

Promethazine tablets should be taken with a full glass of water; food may delay absorption slightly but does not diminish efficacy. The syrup can be measured with a calibrated dropper. Because of its anticholinergic properties, alcohol and other CNS depressants should be avoided to reduce the risk of excessive drowsiness. Through our platform, you can access a printable dosing chart that outlines these recommendations.

Note: Exact dosing must be individualized by a qualified healthcare provider based on the patient’s medical history, concurrent medications, and treatment goals.

Safety Profile & Considerations

Common Side Effects

Drowsiness (occurs in ~30 % of patients)
Dry mouth (≈15 %)
Dizziness or light-headedness (≈10 %)
Blurred vision (≈8 %)
Constipation (≈5 %)

These effects are generally mild and transient, resolving as the body acclimates to the medication.

Serious Adverse Events

Rare but severe reactions include respiratory depression, especially when combined with opioids or other sedatives; extrapyramidal symptoms such as acute dystonia; and anaphylaxis. Any sudden difficulty breathing, swelling of the face, or uncontrolled muscle spasms warrants immediate medical attention.

Contraindications

Known hypersensitivity to promethazine or other phenothiazines.
Concurrent use of monoamine oxidase inhibitors (MAOIs) or within 14 days of stopping an MAOI.
Children younger than 2 years for cough or cold indications (risk of fatal respiratory depression).
Severe central nervous system depression.

Drug Interactions

CNS depressants (e.g., benzodiazepines, barbiturates, alcohol) amplify sedation.
Other antihistamines increase anticholinergic load, raising the risk of dry mouth and urinary retention.
MAO inhibitors can precipitate hypertensive crises.
Anticholinergic drugs (e.g., atropine, certain antidepressants) may intensify blurred vision and constipation.
Opioids: heightened risk of respiratory depression; dose adjustments may be needed.

Special Populations

Pregnancy: Classified as Category C; animal studies show risk, but human data are limited. Use only if potential benefit outweighs risk.
Breastfeeding: Passes into breast milk; may cause infant sedation; consider alternatives.
Elderly: Heightened sensitivity to sedation and anticholinergic effects; start at the lower end of dosing range.
Hepatic or renal impairment: Reduce dose and monitor plasma levels, as metabolism and excretion are slowed.

Frequently Asked Questions

How does promethazine differ from diphenhydramine? Promethazine has a stronger anticholinergic component and additional dopamine antagonism, which gives it more pronounced sedative and anti-emetic properties than diphenhydramine, a pure H₁ antagonist.
How long before promethazine produces noticeable effects for motion-sickness? Oral dosing taken 30 minutes before travel usually yields symptom relief within an hour, while the injectable form can act within 5-10 minutes.
What should I do if I experience severe drowsiness after taking promethazine? Avoid operating machinery or driving, stay hydrated, and contact your physician if drowsiness persists beyond 24 hours or is accompanied by confusion.
Is it safe to consume alcohol while on promethazine? Alcohol can intensify sedation and respiratory depression; it is best to avoid or limit intake while using the medication.
Can promethazine cause weight gain? It is not commonly associated with weight changes, but increased appetite may occur in some individuals due to its antihistaminic effects.
What foods, if any, should I avoid with promethazine? No specific dietary restrictions exist, but grapefruit juice may inhibit metabolic enzymes and modestly increase plasma levels; discuss with your clinician.
How does promethazine affect blood pressure? At therapeutic doses, it has minimal impact on blood pressure, though high doses can cause orthostatic hypotension due to its anticholinergic action.
Is promethazine appropriate for chronic use in eczema? It may be prescribed off-label for severe pruritus in eczema under specialist supervision, but long-term safety data are limited; topical therapies are generally preferred.
What are the signs of an allergic reaction to promethazine? Rash, itching, swelling of the face or throat, and difficulty breathing indicate a possible hypersensitivity reaction and require urgent medical care.
What information should I provide my doctor when discussing promethazine?
- Complete list of current medications, including over-the-counter drugs and supplements.
- History of asthma, liver or kidney disease, and any prior reactions to antihistamines.
- Specific symptoms you hope to treat (e.g., allergy, nausea, motion-sickness).
- Any existing pregnancy or breastfeeding status.

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.