Allergies are one of the most frequent health problems, impacting millions of people around the world every year. Antihistamines, which target the body’s histamine response to allergens, like cetirizine, provide relief for many patients. 

Cetirizine, which produces less sleepiness than previous antihistamines, is well-known for effectively managing symptoms such as hives, itchy eyes, runny nose, and sneezing. For NEET PG aspirants, understanding cetirizine’s pharmacology, uses, safety profile, and interactions is crucial because it is a frequently prescribed drug in clinical practice. 

A clear grasp of its mechanism of action, clinical applications, and precautions can help in patient care and competitive exam performance. This article is a comprehensive guide to cetirizine—covering its therapeutic uses, side effects, precautions, and drug interactions.

Keep reading for a detailed insight.

What is Cetirizine?

Cetirizine is an antihistamine used to treat allergy symptoms, such as a runny nose, itchiness in the nose, throat, eyes, or skin, sneezing, and watery eyes. This drug is available through prescription as well as over-the-counter. 

Cetirizine is a second-generation H1 histamine receptor antagonist (antihistamine) derived from the first-generation antihistamine hydroxyzine. It is used to treat allergy symptoms and works by blocking the receptors of histamine, a chemical released in the body to fight off invading allergens.

Unlike its first-generation counterparts, cetirizine is designed to have fewer sedative effects as it blocks the effects of histamine without crossing the blood-brain barrier to the same extent as the first-generation drugs do.

The H1 receptors on which cetirizine has an inhibitory effect are located on the respiratory smooth muscle cells, vascular endothelial cells, gastrointestinal tract and immune cells. As this drug doesn’t cross the blood-brain barrier to a large extent, it doesn’t significantly affect the neurons of the central nervous system. This produces minimal sedation.

Cetirizine demonstrates signature anti-inflammatory activity and has also been found to lessen the migration of neutrophils and eosinophils.

Pharmacokinetics of Citerazine

Here’s how Citerazine affects the body after administration:

• Absorption: Rapidly absorbed in the gastrointestinal tract. It reaches peak concentration in the plasma at 1 hour. The effects of this drug start at around 20-60 minutes. The effects wear off in 24 hours.
• Distribution: 93% of the cetirizine binds to plasma proteins. It stays in the blood longer and moves into tissues more slowly.
• Metabolism: After consuming the drug, the body changes a part of the drug through a process named oxidative O-dealkylation. The cytochrome P450 (CYP450) liver enzyme does not break down cetirizine.
• Excretion: The half-life of cetirizine is 8.3 hours. It is excreted through the kidneys.

Cetirizine is available under different brand names and as an over-the-counter drug at a lower dose of 5-10 mg and by prescription in higher doses of specialised formulas.

What are the Uses of Cetirizine? 

While cetirizine provides relief from allergy symptoms, it doesn’t prevent them. When the body produces histamine in response to various allergens, it leads to an allergic reaction. By blocking the effects of histamine, cetirizine helps relieve mild to moderate allergy symptoms.

Cetirizine helps manage symptoms of both seasonal allergic rhinitis (due to pollens, grass, tree) and perennial allergic rhinitis (due to mould, dust mites, pet dander) in adults and children.

Cetirizine is used for the following allergy symptoms:

• Constant sneezing
• Runny nose
• Watery eyes 
• Itchy throat or nose

Cetirizine can be used to treat uncomplicated skin issues like hives and itching that arise from chronic idiopathic urticaria. The drug reduces the frequency and severity of the symptoms in individuals.

Cetirizine is also used in combination with other drugs for the symptomatic treatment of flu caused by influenza and respiratory allergy.

The drug is also available in other formulations:

• Intravenous Injection: To treat acute urticaria in patients 6 months or older. 
• Ophthalmic (Eye Drops): To treat allergic conjunctivitis in patients 2 years and above.
• Topical Cetirizine: To treat androgenic alopecia (hair loss)

What are the Side Effects of Cetirizine?

The side effects of cetirizine are not as adverse as those of first-generation antihistamines, but the drug can still cause some side effects:

• Drowsiness or fatigue 
• Excessive tiredness
• Dry mouth 
• Stomach discomfort, like abdominal pain
• Nausea 
• Diarrhea 
• Dizziness 
• Headaches
• Sore throat

It is rare to experience any serious side effects with cetirizine; however, some people report having difficulty breathing and swallowing.

What are the Precautions for Cetirizine Use? 

Some safety considerations need to be taken into account when using cetirizine. Individuals who are allergic to cetirizine or related medications like hydroxyzine should avoid taking the drug. Furthermore, those with kidney, liver, and renal problems should take a lower dose of cetirizine under monitoring.

Cetirizine is considered safe for pregnant women and recommended for those who need antihistamine treatment. However, it should only be used when it’s necessary. When it comes to breastfeeding, prolonged or large doses of cetirizine are known to reduce the supply of breastmilk and cause drowsiness in the infant.

Individuals prescribed ophthalmic cetirizine are advised to remove contact lenses and wait 10 minutes before reinsertion after use. This is because cetirizine hydrochloride contains benzalkonium, which can be easily absorbed by the body and can cause irritation and redness of the eyes.

Since cetirizine can cause drowsiness, it becomes crucial to be cautious while operating cars or performing attention-heavy tasks. The drug is also known to be more sensitive to the geriatric population. For this reason, a lower dose and special monitoring are again recommended.

When it comes to food, unless suggested by the physician, a regular diet should be followed. However, consumption of alcohol can increase the sedative effects of the drug.

Interactions of Cetirizine with Other Drugs 

There are 254 drugs that are known to interact with cetirizine. A brief detail is provided in the table below:

Drug or Substance	Interaction
Sedatives, MAOIs (Monoamine Oxidase Inhibitors), or Other Drowsiness-Causing Medications	May increase sedation
Alcohol and Other CNS (Central Nervous System)Depressants	Can increase drowsiness and slow reaction times.
P-glycoprotein (P-gp) Inhibitors	May affect how much cetirizine stays in the body system, potentially increasing side effects.
Pseudoephedrine Combinations (e.g., Zyrtec-D)	Adds a decongestant effect but may raise blood pressure or heart rate

FAQs about Cetirizine

1. What is cetirizine used for?

Cetirizine is a second-generation antihistamine drug used to manage allergy and urticaria by inhibiting the release of histamine. It helps with symptoms such as sneezing, itchiness, hives, a runny nose or watery eyes.

2. Does cetirizine make you sleepy?

While cetirizine is considered to be less sedative than its first-generation counterpart, it can still cause mild drowsiness. It is usually recommended to avoid operating heavy machinery or driving a car after taking the medication.

3. Can cetirizine be taken every day?

Yes, cetirizine can be taken daily for ongoing allergy relief; however, the medical expert or the package label should follow proper dosage instructions. Under certain conditions, a lower dosage of cetiriine is recommended, such as for individuals with hepatic and renal impairment.

4. Is cetirizine safe during pregnancy or breastfeeding?

Cetirizine appears to be generally safe during pregnancy, but it should only be prescribed when it is necessary. As traces of cetirizine can enter breastmilk and thereby affect the nursing infant, the drug is not recommended for breastfeeding mothers.

5. Can cetirizine be taken with other medications?

Cetirizine can interact with some medicines, especially sedatives, alcohol, and drugs that cause drowsiness. Interaction with other drugs might also worsen the side effects of cetirizine.

Conclusion 

Cetirizine remains a cornerstone in allergy management due to its effectiveness, rapid onset of action, and relatively low sedative effects compared to first-generation antihistamines. For medical professionals and students alike, knowing the mechanism, uses, precautions, and interactions is essential for safe and effective prescribing.

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