Promethazine: characteristics and side effects of this drug

There are many people who have some type of allergy. There are those who cannot eat shellfish or peanuts, or who every spring suffer from rhinitis, congestion and discomfort from the pollen of various plants. Or that they cannot have pets due to allergies to mites or dander present in their fur. And even many people are allergic to some medicine.

If this allergy is known, it is because there has been some type of reaction, sometimes even anaphylaxis, to some stimulus. Although sometimes we are faced with something simply annoying, the truth is that an allergy is not something anecdotal or innocuous, but depending on the case it can have fatal potential.

Although some allergic reactions can be life-threatening, fortunately we have drugs such as promethazine that allow us to reduce inflammatory processes caused by allergy. It is about this specific drug that this article deals with, which is also helpful for other types of problems and conditions.

• Related article: "Types of psychoactive drugs: uses and side effects"

What is promethazine?

Receives the name of promethazine a synthetic antihistamine drug, derived from the phenothiazine family (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 psychoactive drug, it has the property of being able to cross the blood brain barrier in such a way that also has an effect on the nervous system.

This drug is considered first generation, being discovered in a similar way to chlorpromazine (the first synthesized phenothiazine antipsychotic). Despite being a phenothiazine, which are often one of the basic structures from which they develop antipsychotics, in this case your action It does not have a neuroleptic effect that makes it possible to treat psychotic problems.

This drug is metabolized in the liver and is eliminated from the body via the urine and feces. It is available in multiple presentations, suitable for its multiple uses. You can find presentations in the form of tablets or syrup to be administered orally, suppositories for rectal administration and injectables for use intramuscularly or intravenous. Finally, it is worth noting the existence of promethazine cream, for topical use.

Mechanism of action

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

Specifically, its main action is exerted at the level of the histaminergic system, maintaining a competitive antagonistic relationship with histamine. This implies that hinders the action of histamine on the body because it blocks H1 receptors, with which it has less action and its levels are reduced, something that in turn allows reducing inflammatory processes such as those of allergies.

Its action is reversible (that is, its action does not remain in force over time but ceases after a few hours). In addition, it is non-specific, which means that it affects receptors present throughout the body.

In addition to histamine, promethazine also has an anticholinergic action, something that allows it to possess antiemetic properties and contributes to regulating gastric secretions. Although in a minor way it can also affect the aderergic system.

• You may be interested in: "Histamine: functions and associated disorders"

main indications

As an antihistamine that it is, promethazine's main indication is the treatment of medical conditions that occur with tissue inflammation. In this sense, Its main indication is the relief and symptomatic treatment of allergic reactions. in different parts of our body.

Its main use is therefore in contexts in which allergic rhinitis, urticaria, angioedema or conjunctivitis arises. 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 (that is, it short or makes vomiting difficult), so it is also used in the presence of prolonged severe nausea and vomiting in time. In addition It has mucolytic and antitussive action, something useful in catarrhal and flu processes.

It is also regularly used for the prevention and treatment of dizziness of kinetic origin, such as those that appear on plane, boat or car trips.

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 surgical interventions, or to treat post-surgery or postpartum pain.

Possible side effects

Although promethazine is a very useful drug for treating the symptoms of many medical conditions, the truth is that its administration can also lead to the appearance of annoying and even dangerous adverse reactions and side effects.

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

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

It can also cause slowing of the respiratory rate, fever, arrhythmias, fainting, dyskinesias and even convulsions, bleeding, jaundice or problems breathing or swallowing (the latter are serious and require going to to the doctor). It must be taken into account that sometimes it generates uncontrollable movements at the eye level and abnormal positions of the neck and tongue, something that can also be a serious side effect.

Although it is unusual, in some people there is a risk of leukopenia, neutropenia, thrombocytopenia, anemia or agranulocytosis, conditions that require rigorous medical control if they arise due to their danger.

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 can cause tissue death or necrosis.

contraindications

Among the many conditions for which this drug is contraindicated, those who are allergic to promethazine, to phenothiazines or any of its components, as well as those suffering from jaundice, bone marrow depression, or renal or hepatic failure severe. Also is contraindicated in case of epilepsy or in cases of Reye's syndrome.

In the case of intravenous application, it is relevant to bear in mind that it should never be injected into an artery but rather into a vein, given the risk of arteriospasm. It is not recommended in patients with glaucoma or urinary problems. Other subjects who should be especially careful in their use are those who present hypotension or have a tendency to it or those who suffer from prostate hypertrophy.

Also It is contraindicated in infants and children under two years of age., since it has the ability to slow or even stop the breathing rate (something that can have deadly repercussions). In general, it is not recommended except in cases of extreme necessity (the costs and benefits of its administration must be evaluated with the doctor), in cases of pregnancy or lactation since the baby can excrete and generate severe problems, as well as in severely dehydrated or sick minors sharp.

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

Bibliographic references:

• Spanish Agency of Medicine and Health Products (2006). Data sheet. Frinova solution for injection. Drug Information Center.
• 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). Promethazine. Medline Plus [Online]. Available in: https://medlineplus.gov/spanish/druginfo/meds/a682284-es.html.
• Vademecum Spain (2015). Promethazine. Vademecum [Online]. Available in: https://www.vademecum.es/principios-activos-prometazina-r06ad02.