Promethazine: characteristics and side effects of this drug.

A type of phenothiazine-type drug used in allergic reactions.

Many people have some kind of allergy. There are those who cannot eat shellfish or peanuts, or who every spring suffer rhinitis, congestion and discomfort from the pollen of various plants. Or who cannot have pets because of Allergy to dust mites or dander in their fur. And even many people are allergic to medication.

If you know this allergy is because you have had some kind of reaction, sometimes even anaphylaxis, to some stimulus. Although sometimes we are facing something simply annoying, the truth is that an allergy is not something anecdotal or innocuous, but depending on the case it can even have mortal potential.

Although some allergic reactions can even be fatal, fortunately we have drugs such as promethazine that allow us to reduce the inflammatory processes generated by allergy. generated by allergy. It is about this drug in particular that this article is about, which is also helpful for other types of problems and conditions.

What is promethazine?

It is called promethazine a synthetic antihistamine drug, derived from the family of phenothiazines (specifically it is an aminoalkylphenothiazine), whose main function is to reduce histamine levels in the body and thus treat inflammatory processes.

Although it is not specifically a psychopharmaceutical, it has the property of being able to cross the blood-brain barrier in such a way that it also has an effect on the nervous system. has an effect on the nervous system.

This drug is considered a first generation drug, being discovered in a similar way to chlorpromazine (the first phenothiazine antipsychotic synthesized). Although it is a phenothiazine, which is often one of the basic structures from which antipsychotics are developed, in this case its action does not have a neuroleptic effect. does not have a neuroleptic effect to treat psychotic problems..

This drug is metabolized in the liver and eliminated from the body by urinary and fecal routes. It is available in multiple presentations, suitable for its multiple uses. It is possible to find presentations in the form of tablets or syrup for oral administration, suppositories for rectal application and injectables for intramuscular or intravenous use. Finally, it is worth mentioning the existence of promethazine cream for topical use.

Mechanism of action

Promethazine acts in our organism through the regulation of various types of hormones present in our body..

Specifically, its main action is at the level of the histaminergic system, maintaining a competitive antagonistic relationship with histamine. This means that it It hinders the action of histamine on the body because it blocks the H1 receptors, so that it has less effect on the body.This means that histamine has less action and its levels are reduced, which in turn reduces inflammatory processes such as those of allergy.

Its action is reversible (i.e. its action does not remain in force over time but ceases after a few hours). It is also non-specific, which means that it affects receptors present in the whole organism.

In addition to affecting histamine, promethazine also has an anticholinergic action. has an anticholinergic actionThis allows it to possess antiemetic properties and contribute to regulate gastric secretions. Although to a lesser extent it can also affect the aderenergic system.

Main indications

As an antihistamine, promethazine's main indication is the treatment of medical conditions involving tissue inflammation. In this sense, its main indication is the relief and symptomatic treatment of allergic reactions in different parts of our body. in the different parts of our organism.

Its main use is therefore in contexts in which rhinitis, urticaria, angioedema or allergic conjunctivitis arise. It is also useful in the treatment of contact dermatitis, and its use is especially relevant in the case of anaphylaxis.

In addition to its antihistamine action, this substance has an antiemetic effect (i.e. it stops or hinders vomiting), so it is also used in the presence of severe nausea and vomiting prolonged in time. In addition, it has mucolytic and antitussive action, something useful in catarrhal and flu-like processes..

It is also commonly used for the prevention and treatment of dizziness of kinetic origin, such as those that appear when traveling by plane, boat or car.

Another of its applications or functionalities can be found in its use as a local anesthetic, since it has sedative properties. In this sense it has been used to relax the person before surgery, or to treat post-surgical or postpartum pain.

Possible side effects

Although promethazine is a very useful drug for the treatment of the symptoms of many medical conditions, its administration can also lead to the development of adverse reactions and uncomfortable and even dangerous side effects. side effects and adverse reactions, which can be bothersome and even dangerous..

One of the most common is sedation and drowsiness. In addition, the fact that histamine and acetylcholine levels are affected can lead to symptoms such as fatigue, insomnia, blurred vision, dry mouth, motor incoordination, hyperactivity or hypomania.hyperactivity or hypomania, among others. Vertigo, tremors, visual problems, hypotension or urinary retention are other possible secondary symptoms.

It should be taken into account that it may increase photosensitivity, so it is recommended not to be excessively exposed to sunlight after administration.

It can also cause slowing of the respiratory rhythm, fever, arrhythmias, fainting, dyskinesias and even convulsions, hemorrhages, jaundice or breathing or swallowing problems (the latter are serious and require medical attention). It should be noted that it sometimes causes uncontrollable eye movements and abnormal neck and tongue positions, which can also be a serious side effect.

Although rare, in some people there is a risk of leukopenia, neutropenia, thrombocytopenia, anemia or agranulocytosis, conditions that require rigorous monitoring.These conditions require rigorous medical control in case of occurrence due to their dangerousness.

It should never be applied intra-arterially, since there is a risk of severe arteriospasm and the appearance of gangrene. The subcutaneous route should be avoided as it may cause tissue death or necrosis.

Contraindications

Among the many conditions in which this drug is contraindicated, those who are allergic to promethazine, phenothiazines or any of its components, as well as those who suffer from jaundice, bone marrow depression or severe renal or hepatic insufficiency stand out in the first place. Also It is also contraindicated in case of epilepsy or Reye's syndrome..

In the case of intravenous application, it is important to take into account that it should never be injected into an artery but into a vein, due to the risk of arteriospasm. It is not recommended in patients with glaucoma or urinary problems. Other subjects who should be especially cautious in its use are those who present hypotension or have a tendency to it or those who suffer from prostate hypertrophy.

Also It is also contraindicated in infants and children under two years of age.It can slow down or even stop the respiratory rhythm (something that can have fatal repercussions). In general, it is not recommended except in cases of extreme necessity (the costs and benefits of its administration should be evaluated with the physician), in cases of pregnancy or lactation since it can be excreted in the baby and generate severe problems, as well as in severely dehydrated or acutely ill children.

Finally, the feasibility of treatment with promethazine should be consulted with the physician if other drugs are being used, since they may present interactions. Among others, it should not be mixed with alcohol, MAOIs, neuroleptics of the same family, sedatives, morphine or depressant substances. Finally it should be taken into account that due to its sedative effects, driving or the use of heavy machinery should be avoided.

Bibliographic references:

• Agencia Española de Medicina y Productos Sanitarios (2006). Ficha técnica. Frinova solución inyectable. Centro de Información de Medicamentos.
• Kamei, H., Isaji, A., Noda, Y., Ishikawa, K., Senzaki, K., Yamada, K., Sugiura, K., Tomita, Y. & Nabeshima, T. (2012). Effects of single therapeutic doses of promethazine, fexofenadine and olopatadine on psychomotor function and histamine-induced wheal- and flare-responses: a randomized double-blind, placebo-controlled study in healthy volunteers. Arch Dermatol Res., 304(4): 263 - 272.
• National Institute of Health. (2017). Prometazina. MedlinePlus [Online]. Disponible en: https://medlineplus.gov/spanish/druginfo/meds/a682284-es.html.
• Vademecum Spain (2015). Prometazina. Vademecum [Online]. Disponible en: https://www.vademecum.es/principios-activos-prometazina-r06ad02.