Promethazine: Price, Dosage & Where to Buy

Promethazine is a first-generation antihistamine of the phenothiazine class, used to relieve allergy symptoms such as seasonal or year-round allergic rhinitis. It can also cause drowsiness, which matters when driving or using machinery, and has other labelled uses including motion sickness and nausea associated with surgery. Promethazine is available as a generic medicine and requires a prescription in the United Kingdom.

Promethazine is used for seasonal and year-round allergic rhinitis, as well as vasomotor rhinitis, which causes nasal symptoms. Its allergy indications also include allergic eye inflammation caused by inhaled allergens or foods, mild uncomplicated hives and allergic swelling, and dermographism, where rubbing or scratching the skin produces raised marks. It can help relieve allergic reactions to blood or plasma.

For anaphylactic reactions, it is an additional treatment alongside adrenaline and standard measures after the acute symptoms have been controlled, not a replacement for emergency treatment. Other labelled uses include preventing and treating motion sickness, controlling nausea and vomiting associated with certain anaesthetics and surgery, and providing sedation before or after surgery or during obstetric care. It is also used alongside pain medicines after surgery and for sedation and relief of apprehension.

Promethazine blocks H1 histamine receptors. Histamine is a chemical messenger involved in allergic reactions, and blocking its effects helps reduce symptoms such as itching, raised skin reactions and nasal irritation. As a first-generation antihistamine, it also enters the brain, where its effects can cause drowsiness and sedation.

Effects on signalling involved in balance and nausea help explain why this class can reduce motion sickness. It also has anticholinergic effects, meaning it reduces some actions of another chemical messenger called acetylcholine; these effects can contribute to dry mouth and blurred vision.

The label lists oral tablets and rectal suppositories in strengths of 12.5 mg, 25 mg and 50 mg. The label lists oral solution and syrup at 6.25 mg/5 mL, and injection preparations at 25 mg/mL and 50 mg/mL. The label lists an average oral allergy dose of 25 mg before retiring, with 12.5 mg before meals and on retiring as an alternative when necessary.

The label lists an average adult motion sickness dose of 25 mg twice daily. The label lists an average effective dose of 25 mg for active treatment of nausea and vomiting, with repeat doses of 12.5 mg to 25 mg when necessary. The label lists adult sedation doses of 25 mg to 50 mg for night-time, presurgical or obstetric use.

These are label facts, not an individual treatment plan. Dosing depends on the reason for treatment and the patient's circumstances, and the label calls for adjustment to the smallest amount adequate to relieve symptoms. Tablets are contraindicated in children under 2 years of age.

For a regularly scheduled treatment, usual pharmacy guidance is to resume the prescribed schedule when a dose is missed, avoiding a double dose to make up for it. If the next dose is nearly due, the missed dose is generally skipped. For occasional use or uncertainty about timing, ask a pharmacist for advice.

There are no adequate, well-controlled studies of promethazine tablets in pregnant women. The label states that use during pregnancy should be considered only when the potential benefit justifies the potential risk to the fetus.

Use within two weeks of delivery may inhibit platelet aggregation in the newborn, affecting the way platelets clump together. The label does not establish safety during breastfeeding; discuss pregnancy or breastfeeding with a doctor or pharmacist.

The label specifies storage at 20°C to 25°C, protected from light. Keep the container tightly closed. Tablets should be kept in a light-resistant, tight container to maintain quality.