Oral Antihistamines: Be free from allergy misery


No more allergy misery

What does oral antihistamine do?

Oral antihistamines are medications used to treat allergies. They are also sometimes prescribed to people who suffer from chronic hives. Oral antihistamines are usually taken once daily at bedtime.

There are several types of oral antihistamines. Some are designed to relieve allergy symptoms, while others are intended to prevent allergic reactions.

Are They Safe For Children?

Anti-allergy medications are used to treat allergies, hay fever, colds, and other conditions. However, there has been a lot of controversy surrounding the safety of these drugs for children.

Many parents wonder if their child needs an anti-allergy medication, especially if they are under two years old. The answer to this question depends on several factors, including the severity of the allergy symptoms, whether or not the child is experiencing any side effects, and whether or not a doctor has prescribed the medication.

Oral antihistamines for dogs

Oral antihistamines are used to treat allergies in dogs. They are also used to prevent itching and to scratch in dogs that suffer from flea allergy dermatitis.

Two types of oral antihistamines are commonly prescribed for dogs: first-generation and second generation. Both types are effective at treating allergies in dogs. However, there are differences between the two.

First-generation antihistamines are considered safer because they are less likely to cause side effects such as drowsiness. Second-generation antihistamines are more potent and therefore more likely to cause side effects.

Oral antihistamines and their side effects

Oral antihistamines are commonly used to treat seasonal allergies, hay fever, and other forms of allergic rhinitis. As an added benefit, these medications also reduce symptoms of colds and flu.

However, certain types of oral antihistamines can cause serious side effects if taken incorrectly.

These side effects include drowsiness, dry mouth, nausea, headaches, blurred vision, and constipation. In some cases, these side effects can even lead to addiction.

If you’re using an oral antihistamine for the first time, be sure to read the medication’s label carefully before taking it. If you notice any side effects, speak to your doctor immediately.

How long does it take for an oral antihistamine to work

The onset of action varies depending on the type of antihistamine being used. There are three main categories of antihistamines: H1 blockers, H2 antagonists, and leukotriene modifiers. Each class works differently, but all have similar benefits.

H1 blocker

An H1 antagonist blocks histamine receptors located within cells throughout the body. This means that when applied topically, H1 blockers will help alleviate itchiness caused by insect bites and poison ivy rashes. When ingested, however, H1 blockers only affect the stomach lining where acidity levels are lower than those found elsewhere in the digestive tract. Therefore, H1 blockers cannot effectively block histamine receptors inside the gut wall.

When administered orally, H1 blockers act quickly on the brain. Within minutes of swallowing them, users begin feeling relief from sneezing, runny nose, watery eyes, and stuffy sinuses.

Side effect profile

Because H1 blockers do not penetrate the bloodstream, they rarely produce sedative or psychotropic effects like many other prescription drugs. Instead, they tend to make people feel alert and energetic. Common side effects associated with H1 blockers include headache, dizziness, nervousness, anxiety, insomnia, agitation, restlessness, irritability, diarrhea, heartburn, indigestion, abdominal pain, flatulence, bloating, cough, vomiting, rash, urticaria, pruritus, and ushing. Some patients may experience tachycardia.

H2 receptor antagonist

When swallowed, H2 receptor antagonists travel through the gastrointestinal system without affecting its contents. Once absorbed, they enter circulation and reach target organs via blood vessels. Because they pass directly through the liver, most H2 receptor antagonists undergo little metabolism once they arrive at their destination. Consequently, they usually stay active longer than conventional antihistamines.

Like H1 blockers, H 2 receptor antagonists relieve nasal congestion, wheezing, coughing, and sneezing. Unlike H 1 blockers, H2 receptor antagonists also protect against asthma attacks. Side effects vary widely among different brands of H2 receptor antagonists. For example, cimetidine tends to leave users feeling tired, while ranitidine makes them feel energized.

Leukotriene modifier

These medications inhibit a chemical called leukotrienes, which play a role in allergic reactions such as hay fever. Leukotrienes cause inflammation, swelling, mucus production, and itching. They can also trigger asthma symptoms. By blocking these chemicals, leukotriene inhibitors prevent the formation of new ones. As a result, fewer allergy-related problems occur. However, because leukotriene modulators don’t treat existing allergies, they should never replace traditional treatment methods prescribed by allergists.

Side effect profile

The most common adverse events reported with leukotriene inhibitor use were nausea, dry mouth, constipation, drowsiness, fatigue, headaches, backache, and throat irritation.

Who should not take antihistamines

People who have had an anaphylactic shock after taking any medication should avoid all forms of antihistamines. These individuals must seek immediate medical attention if they develop severe respiratory distress such as difficulty breathing, chest tightness, rapid heartbeat, or low blood pressure.

Other contraindications for using antihistamines include:

• People with known sensitivity to antihistamines;

• Those suffering from chronic obstructive pulmonary disease ;

• Pregnant women;

• Children under 12 years old;

• Anyone over 65 years old;

• Patients with cardiovascular disorders including high blood pressure, angina pectoris, and arrhythmias;

• Individuals with peptic ulceration;

• Diabetics;

• Hypersensitivity to sulfonamides or antacids;

• History of seizures;

• Any condition involving an increased risk of bleeding;

• Women who are pregnant or nursing;

• Active hepatic disease ;

• Severe renal impairment;

• Chronic alcohol abuse;

• Use of MAOIs within 14 days before starting therapy;

• A history of drug dependence or addiction;

• Persons on concurrent antidepressant therapy;

• Concurrent use of corticosteroids;

What is it used for?

Antihistamine drugs work best when given before exposure to triggers that produce histamine release. When taken regularly, antihistamines reduce the amount of histamine released during an attack. This helps keep you symptom-free until your next dose.

The main types of antihistamines available today include:

Cetirizine hydrochloride


Hydroxyzine hydrochloride



Consult a doctor before use!


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