Propiomazine is an antihistamine

Antihistamine

An H1 antagonist is a histamine antagonist of the H1 receptor that serves to reduce or eliminate effects mediated by histamine, an endogenous chemical mediator released during allergic reactions...

 blocking H1 receptors. It is used to treat insomnia

Insomnia

Insomnia is most often defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions:...

, and to produce sleepiness or drowsiness and to relieve anxiety before or during surgery

Surgery

Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...

 or other procedures and in combination with analgetics also during labor

Childbirth

Childbirth is the culmination of a human pregnancy or gestation period with the birth of one or more newborn infants from a woman's uterus...

. Propiomazine is a phenothiazine

Phenothiazine

Phenothiazine is an organic compound that occurs in various antipsychotic and antihistaminic drugs. It has the formula S2NH. This yellow tricyclic compound is soluble in acetic acid, benzene, and ether. The compound is related to the thiazine-class of heterocyclic compounds...

, but is not used as a neuroleptic because it does not block dopamine receptors well.

Mechanism of action

Propiomazine is an antagonist at types 1, 2, and 4 dopamine receptors, serotonin (5-HT) receptor types 2A and 2C, muscarinic receptors 1 through 5, alpha(1)-receptors, and histamine H1-receptors. Propiomazine's antipsychotic effect is due to antagonism at dopamine and serotonin type 2 receptors, with greater activity at serotonin 5-HT2 receptors than at dopamine type-2 receptors. This may explain the lack of extrapyramidal effects. Propiomazine does not appear to block dopamine within the tubero-infundibular tract, explaining the lower incidence of hyperprolactinemia than with typical antipsychotic agents or risperidone.

Side effects

Rare, serious side effects include convulsions (seizures); difficult or unusually fast breathing; fast or irregular heartbeat or pulse; fever (high); high or low blood pressure; loss of bladder control; muscle stiffness (severe); unusual increase in sweating; unusually pale skin; and unusual tiredness or weakness.

Drowsiness is a usual side effect, and propiomazine was blamed on Kerry Katona

Kerry Katona

Kerry Jayne Elizabeth Katona is an English media personality and singer best known for her television work, predominantly in light entertainment and reality shows. She has also been a pop singer with girl group Atomic Kitten, a magazine columnist, an actress, and the author of ghostwritten books...

's October 2008 interview on This Morning

This Morning (TV series)

This Morning is a British daytime television programme broadcast on ITV. As of September 2011, its main presenters are Phillip Schofield and Holly Willoughby, and Ruth Langsford and Eamonn Holmes, with various other presenters standing in for illness or contributing to sections of the programme.The...

where she was accused of being under the influence of drink or drugs, as she appeared slurred and drowsy.