Antihistamines – action, types, indications, side effects

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Antihistamines are used by people who struggle with various types of allergies. Symptoms of allergies appear under the influence of histamine. Antihistamines are there to block the histamine receptor. Nevertheless, drugs are a half-measure because they reduce the symptoms of allergy, but they do not address the causes of the disease. Among other things, antihistamines help against seasonal hay fever.

Antihistamines – allergy

Our body protects us from many dangers. For example, the ribs protect the heart and lungs from injury. In turn, the skin protects the body from external factors such as sun, wind and bacteria that can cause disease and infection, while eyelashes protect the eyes from pollution. It is also impossible not to mention the immune system that fights substances that enter our body, and which are considered “foreign”.

Allergy occurs when the immune system overreacts to a “foreign” substance. In the case of allergies, we are disturbed by substances that are usually harmless and do not bother some people, such as dust or animal hair. Our body perceives these substances as ‘foreign’, which then causes an overreaction of the body’s defense system, which includes the release of histamine. Substances that cause an overreaction are called allergens. The symptoms that arise are called an allergic reaction.

Also check: How does the immune system work?

Antihistamines – histamine

Histamine is an important chemical that plays a role in many different processes in the body. It stimulates the secretion of gastric acid, plays a role in inflammation, dilates blood vessels, affects muscle contractions in the intestines and lungs, and affects the heart rate. It also helps transmit messages between nerve cells and helps fluids travel through the walls of the blood vessels. Histamine is also released if the body encounters an allergen threat. Histamine causes blood vessels to swell and widen, which leads to allergy symptoms.

The most common things that can cause an allergic reaction in some people are:

1. groceries;
2. short;
3. pollen;
4. pet hair, saliva or urine;
5. insect bites and stings;
6. latex;
7. certain drugs and substances.

Too much histamine, caused by the body being hypersensitive and overreacting to an allergen, causes various symptoms. These symptoms can include:

1. cough;
2. wheezing, shortness of breath;
3. tiredness;
4. itchy skin, hives and other skin rashes;
5. itchy, red, watery eyes;
6. runny or blocked nose or sneezing;
7. insomnia;
8. nausea and vomiting.

Antihistamines are drugs that block some of the effects of histamine.

See also: How to recognize an allergic rash? Causes, symptoms and treatment of skin allergies

Antihistamines – types

Antihistamines are divided into two main types. The first subtype is known as H1 receptor antagonists or simply H1 antihistamines. This subtype of antihistamines is used to treat allergy symptoms.

The second subtype is called H2 receptor antagonists or H2 antihistamines. They are used to treat gastrointestinal conditions including gastroesophageal reflux disease [GERD], peptic ulcer, gastritis, motion sickness, nausea and vomiting. The naming structure (H-1 and H-2) tells doctors and scientists about the type of cell where the histamine receptor is located that the antihistamine drug is blocking.

The H1 receptor antagonist subtype is further classified into two groups – first generation antihistamines and second generation antihistamines.

First-generation antihistamines act on the histamine receptor in the brain and spinal cord along with other types of receptors. The most notable thing about this generation of antihistamines is that they cross the blood-brain barrier, which causes drowsiness.

Second-generation antihistamines do not cross the blood-brain barrier to the same extent as the first generation and therefore do not cause drowsiness at standard dosage levels. Second-generation antihistamines are considered safer than first-generation antihistamines because they do not cause drowsiness and interact with fewer medications.

It is worth mentioning here that the newest second-generation antihistamines (fexofenadine, desloratadine, levocetirizine, bilastine) are sometimes called third-generation drugs. They are characterized by a small number of interactions with other drugs, supplements or food products.

Also read: The secret of the tight blood-brain barrier

First and second generation antihistamines

There are many first-generation prescription and over-the-counter antihistamines. A few examples of first-generation over-the-counter and prescription antihistamines include:

1. chlorfeniramina;
2. clemastine;
3. cyproheptadyna;
4. dimenhydrynat;
5. difenhydramina;
6. coksylamina;
7. hydroxyzine;
8. schedule.

A few examples of over-the-counter and prescription antihistamines of the second and third generation include:

1. azelastyna;
2. loratadyna;
3. cetirizine;
4. bilastine;
5. rupatadyna;
6. desloratadyna;
7. feksofenadyna.

Antihistamines – application

In addition to, of course, the allergy itself, antihistamines are also used for other conditions.

H1 receptor antihistamines treat:

1. allergic rhinitis / hay fever;
2. allergic conjunctivitis;
3. hives and other skin rashes;
4. cold;
5. food allergies;
6. hypersensitivity to certain medications;
7. insect bites and stings.

First-generation H1 antihistamines also treat:

1. insomnia;
2. motion sickness;
3. bow.

H2 receptor antihistamines treat:

1. heartburn;
2. gastroesophageal reflux disease (GERD);
3. duodenal and stomach ulcers;
4. Zollinger-Ellison syndrome.

Other medical conditions treated with antihistamines include:

1. anorexia;
2. headaches;
3. anaphylaxis;
4. dizziness;
5. Parkinson’s disease (to reduce stiffness and tremors);
6. certain types of bone pain.

Your doctor may prescribe antihistamines even for other medical conditions.

Antihistamines – side effects

Antihistamines can be divided into older first-generation drugs and newer second-generation drugs. The former, due to their wider action and influence on various receptors, may cause side effects. The side effects of taking first-generation antihistamines include, among others, the aforementioned drowsiness or reflex disorders. However, these are not the only side effects. They may concern the nervous system, liver or hematopoietic system. It is also likely that your appetite will increase or you will gain weight.

Some of the common side effects of first-generation antihistamines also include: dry mouth and dry eyes; blurred or double vision; dizziness and headache; low blood pressure; mucus thickening in the airways, increased heart rate, difficulty urinating and constipation.

Second-generation antihistamines are newer and generally safe, and do not cause many side effects. They are the basis of antiallergic therapy, which is related to their anti-inflammatory effect and influence on the natural course of allergic diseases.

Some of the common side effects of second-generation antihistamines include: headache, cough, fatigue, sore throat, abdominal pain or discomfort, and nausea or vomiting.

However, the above-mentioned side effects result from the action of antihistamines acting on the H1 receptor. In turn, the common side effects of antihistamines affecting the H2 receptor include: drowsiness, joint or muscle pain, headache, confusion (in the elderly), dizziness, and breast swelling and tenderness.

There are not only prescription drugs available on the market (eg Zyrtec Krople), but also those that can be purchased without a prescription. These include those that include:

1. cetirizine, which inhibits the action of histamine; we find it in a drug called Zyrtec UCB;
2. loratadine relieves the symptoms of hay fever by unblocking a stuffy nose and stopping the sneezing reflex; medicines that contain it are Aleric, Loratadine.

Available forms of antihistamines

Antihistamines come in several forms, including:

1. fluids;
2. balsamic;
3. syrups;
4. gels;
5. eye drops;
6. tablets;
7. aerozolach do nosa;
8. creams;
9. capsules;
10. suppositories.

How to choose an antihistamine drug?

Since there are so many antihistamines, both over-the-counter and prescription, and because they are used to treat a wide variety of health conditions, you may need help figuring out which drug to take. For minor ailments, you can probably go for over-the-counter products. You can read the package labeling and match the symptoms with the labeled symptoms. However, never hesitate to ask your pharmacist for help. They are highly educated in the effects and side effects of drugs. You may need to try different antihistamines (but not more than one at a time, unless your doctor tells you to do so) to find the best drug to deal with your symptoms.

If you need a prescription antihistamine, please check with your doctor to determine which medication is best for you. Many medications interact with antihistamines, so your doctor will want to know what conditions you are suffering from and what medications you are currently taking. The specialist will also want to know if the patient is pregnant, planning to become pregnant, or breastfeeding. Some antihistamines are not recommended in pregnancy as they can cause birth defects in very high doses. Antihistamines can pass into breast milk, so consult your doctor before taking antihistamines if you are breastfeeding.

Also check: Over-the-counter drugs. Are you taking them safely?

Antihistamines – contraindications

In the case of first-generation antihistamines, the contraindications include:

1. glaucoma;
2. prostate hypertrophy;
3. bone marrow damage;
4. hypersensitivity to the drug.

In the case of second-generation antihistamines, the contraindications are:

1. hypersensitivity;
2. heart problems (in some cases).

Remember to read the leaflet carefully before using the medicine.

Antihistamines – overdose

In the case of antihistamines, overdosing can cause symptoms such as:

1. dizziness;
2. dry mouth;
3. feeling sleepy;
4. tiredness;
5. weakness.

In addition, it is also possible to:

1. depression of the adrenal glands causing muscle weakness;
2. increased salt demand;
3. reducing blood sugar levels;
4. darker color of the skin;
5. depression.

Antihistamines for children

Allergy may appear in the youngest years of a person’s life. Antihistamines for children can be used only when recommended by a doctor who will determine a dose that is safe for a small patient. In a situation where we notice symptoms indicating an allergy in a child, it is worth consulting a pediatrician or an allergist.

Read also: Warning, these drugs can be dangerous to children

Antihistamines – drug interactions

People with HIV, tuberculosis and those treating fungal infections should be careful about drug interactions. It can also be dangerous to combine allergy medications with antacids. This is because antacids may cause the antihistamine to be absorbed in smaller amounts.

Antihistamines – Frequently Asked Questions

Can antihistamines cause constipation?

Yes, some antihistamines, such as diphenhydramine, cause constipation as a side effect.

Can antihistamines cause depression?

One study of 92 people with chronic itching found that patients who took the antihistamines cetirizine and hydroxyzine reported increases in depression and anxiety. The effect of all antihistamines on mood disorders has not yet been studied.

Can Antihistamines Cause High Blood Pressure?

If you are already taking medications for high blood pressure, combining them with an antihistamine can increase your heart rate and raise your blood pressure. Talk to your doctor about your options.

Can antihistamines cause weight gain?

In addition to calming down and dry mouth, antihistamines can have the undesirable side effect of increased appetite and weight gain. This may be due to the similar chemical structure of antihistamines and some psychiatric drugs, such as antidepressants, known to increase appetite and lead to weight gain.

Many people who have used levocetirizine have reported an increase in appetite and weight gain. This side effect is believed to occur in only 0,5% of the people in the studies who took the drug. Older antihistamines such as cyproheptadine have actually been used to increase appetite and weight gain in underweight children and cancer patients undergoing chemotherapy.

What antihistamines can I take together?

Antihistamines should not be combined, unless directed by a doctor, the drugs themselves will be taken under his guidance and supervision. Antihistamines should only be used as directed, otherwise serious side effects may occur.

What should I do if my antihistamines are not working?

Talk to your doctor, pharmacist or allergist to help us find treatments for allergies. Some allergies can be treated with decongestants or immunotherapy.

Can I take antihistamines while pregnant or breastfeeding?

It is safest to talk to your doctor if you are pregnant, planning to become pregnant, or are breastfeeding. Animal studies have shown that some antihistamines can cause birth defects. Small amounts of antihistamines are passed on to the baby during breastfeeding. For these reasons, your doctor will want to talk to you and make careful choices if there are any concerns about your or your baby’s safety.

Can you become addicted to antihistamines?

Antihistamines are generally considered safe for daily use and have a low risk of addiction. However, there are reports that people become addicted to certain types of antihistamines. In particular, diphenhydramine, which is a first-generation antihistamine, can lead to withdrawal symptoms when taken in high doses for long periods of time. If you are concerned about the use of antihistamines, consult your doctor.

Do antihistamines cause dementia?

Long-term use of some antihistamines may increase the risk of dementia. Diphenhydramine blocks the action of a neurotransmitter called acetylcholine. This neurotransmitter is essential for remembering and learning. In a 2010 study in the Journal of Child and Adolescent Psychopharmacology of 3000 patients followed for seven years, diphenhydramine increased the risk of dementia by 54%.

Antihistamines – Natural Alternatives

Antihistamines are effective in relieving symptoms, but can cause side effects such as sleepiness and nausea. As a result, some allergy sufferers may find relief by using natural plant extracts and foods that act as antihistamines.

Vitamin C

Vitamin C strengthens the immune system. It also works as a natural antihistamine.

According to a 2018 study published in the Journal of International Medical Research on vitamin C in the treatment of allergies, oxidative stress plays a key role in allergic disease. Since vitamin C is a powerful antioxidant and anti-inflammatory agent, it can act as an allergy medicine. Scientists observed that high doses of intravenous vitamin C reduced allergy symptoms. They also reported that vitamin C deficiency can lead to allergy-related diseases.

The vitamin is present in many fruits and vegetables, incl. in citrus fruits, peppers, tomatoes, strawberries or broccoli.

Also read: Do you like oranges and mandarins? Eat them with white crusts

Butterbur

Butterbur is a plant extract from a shrub that grows in Asia, Europe, and some parts of North America. People often use butterbur to treat migraines and hay fever, also known as allergic rhinitis.

According to the National Center for Complementary and Integrative Health (NCCIH), butterbur may have an antihistamine effect.

A 2007 study review published in the Annals of Allergy, Asthma & Immunology, including 16 randomized, controlled trials testing 10 herbal products, suggests that butterbur may be an effective herbal remedy for hay fever. This review suggested that butterbur was better than placebo or as effective as antihistamines in relieving allergy symptoms. However, the review’s authors note that some large studies have received funding from industrial producers, so further independent research is needed.

Bromelain

Bromelain is an enzyme found in pineapple core and juice and is also available as a supplement. Bromelain is also a popular natural remedy for swelling or inflammation, especially of the sinuses, and following injuries or surgery. A 2013 study in Evidence-Based Complementary and Alternative Medicine suggests that bromelain may reduce allergic sensitization and allergic respiratory disease through its anti-inflammatory and anti-allergic properties.

probiotics

Probiotics are microorganisms that can offer health benefits by helping the body maintain a healthy balance of gut bacteria. Probiotics can boost the human immune system, which can help the body fight allergies. However, the National Center for Complementary and Integrative Health says the evidence for probiotics is mixed and that some probiotics may help and others may not.

Kwercetyna

Quercetin is an antioxidant flavonoid found in many plants and foods. Research suggests that adding quercetin to your diet may help relieve allergy symptoms.

A 2016 study, published in the journal Molecules, suggests that quercetin may have antiallergic and antihistamine properties. In turn, in one animal study, researchers found that quercetin could reduce the effects of respiratory allergies in mice by reducing airway inflammation.

However, the evidence for its effectiveness is mixed, and according to the previously mentioned NCCIH, there is insufficient evidence to suggest that quercetin may alleviate allergic rhinitis. Quercetin is naturally present in many foods and herbs, including apples, blueberries, black and green tea, and grapes.

Antihistamines and immunotherapy

People with severe allergies may benefit from immunotherapy. This treatment is also appropriate if antihistamines do not improve symptoms.

Your healthcare professional will give you a series of injections that contain small amounts of the allergen during immunotherapy. This procedure may take several years to numb the body against the allergen. Doctors may recommend sublingual immunotherapy for people allergic to pollen. This involves placing the tablet under your tongue until it dissolves.

See also: Immunotherapy in the fight against the most severe cancers. The research results give hope