Active Ingredient

Phenergan contains the active ingredient promethazine hydrochloride. It is classified as a first-generation antihistamine and belongs to the phenothiazine class of drugs. Promethazine hydrochloride exhibits antihistaminic, sedative, antiemetic, and anticholinergic properties.

Formulations Available

Phenergan is available in multiple formulations including tablets, syrups, suppositories, and injectables. Tablets are commonly available in 12.5 mg, 25 mg, and 50 mg strengths. The syrup formulation typically contains 6.25 mg per 5 mL. Suppositories are often available in 12.5 mg, 25 mg, and 50 mg as well. Injectable forms are provided in 25 mg/mL and 50 mg/mL concentrations.

Indications and Uses

Phenergan is prescribed for numerous conditions including allergic reactions, motion sickness, nausea and vomiting prophylaxis, pre- and post-operative sedation, and adjunctive therapy for pain management. It is also used to treat symptoms of the common cold and as a nighttime sedative.

Mechanism of Action

Promethazine blocks the histamine H1 receptors, preventing the effects of histamine that cause allergic symptoms. Its antiemetic properties are due to its action on the dopaminergic receptors in the brain’s chemoreceptor trigger zone. The sedative effect is derived from its central anticholinergic action.

Administration Guidelines

Phenergan should be administered according to the prescribed dosage and schedule. Tablets should be taken with water, with or without food. Syrup should be measured with a proper dosing spoon or cup. Suppositories should be inserted rectally as instructed. Injectable forms should be administered by healthcare professionals.

Dosage Information

For allergy relief, the typical adult dose ranges from 25 mg to 50 mg taken at bedtime or in divided doses. For motion sickness, 25 mg is taken 30 to 60 minutes before travel and may be repeated every 12 hours. For nausea and vomiting, 12.5 mg to 25 mg every 4 to 6 hours is recommended. As a sedative, 25 mg to 50 mg at bedtime is common.

Storage Instructions

Phenergan should be stored at room temperature, away from light and moisture. Tablets and syrup should be kept in a tightly closed container. Suppositories should be stored in their original packaging and avoided from excessive heat. Injectable forms need to be stored as per specific guidelines indicated on the packaging.

Interactions with Other Drugs

Phenergan can interact with several medications including monoamine oxidase inhibitors (MAOIs), barbiturates, narcotic pain medications, sedatives, and tranquilizers. Concurrent use with alcohol can increase sedative effects. It may also interact with other anticholinergic drugs and antipsychotics, amplifying their side effects.

Precautionary Measures

Patients should inform their healthcare provider of a history of asthma, sleep apnea, glaucoma, or high blood pressure. It should be used cautiously in those with obstructive diseases of the gastrointestinal or genitourinary tracts. Elderly patients may exhibit heightened sensitivity to its effects.

Pediatric Use

Phenergan is not recommended for children under 2 years due to risks of severe respiratory depression. Dosage for children over two years should be carefully adjusted depending on the age, weight, and condition being treated. Close monitoring is advised for signs of respiratory difficulties.

Pregnancy and Lactation

Phenergan is classified under Pregnancy Category C. It should be used only if the potential benefits justify the potential risks to the fetus. Promethazine may pass into breast milk and could harm a nursing infant. Nursing mothers should consider either discontinuing the drug or stopping breastfeeding.

Adverse Effects

Common side effects include drowsiness, dizziness, dry mouth, blurred vision, and constipation. Severe side effects may include respiratory depression, severe sedation, seizures, and neuroleptic malignant syndrome. Overdose symptoms may consist of severe dizziness, fainting, seizures, or difficulty breathing. Immediate medical attention is necessary for severe adverse reactions.