No. 1 trending search! Loratadine suddenly became popular. What is so special about this drug?

Recently, sneezing, nasal congestion, itchy nose... have begun to "harass" the lives of patients with allergic rhinitis (allergic rhinitis). In order to relieve the symptoms, many citizens urgently took out "loratadine tablets". Today, the topic # loratadine # has even become a hot search on Weibo, attracting everyone's attention.

Weibo screenshot

In addition to loratadine, many netizens pointed out in the Weibo comment area that "cetirizine" can also fight allergies, which also caused some netizens to wonder, what is the difference between loratadine and cetirizine? What matters need to be paid attention to when taking the medicine? Today we will interpret these issues one by one.

Loratadine and cetirizine

What kind of medicine is it?

Loratadine and cetirizine are both antihistamines . In addition to anti-allergic effects, these drugs are also used for urticaria, allergic conjunctivitis, and obvious itching after mosquito bites.

When we have urticaria, allergic rhinitis and other conditions, the body's immune system will release a substance called "histamine", which will then bind to the histamine receptors in the body, causing us to experience discomfort such as itching, sneezing, and runny nose.

Antihistamines , as the name suggests, are drugs that can prevent histamine from binding to receptors, making it unable to exert its effect.

More than 100 years ago, scientists discovered histamine and soon discovered its role in allergic reactions. Regarding antihistamines, Italian pharmacologist Daniel Bovet discovered the first synthetic compound with antihistamine effects, which can protect guinea pigs from histamine-induced allergic reactions. However, due to the toxicity of the compound, it was not used clinically, but it laid the foundation for the subsequent development of antihistamines.

Antihistamines ≠ anti-allergic drugs

Antihistamines refer to drugs that prevent histamine from exerting its effects. Histamine is not only involved in allergic reactions, but also in the occurrence of other diseases. Therefore, antihistamines may be used in addition to allergies as well as in other situations.

Antiallergic drugs do not have this category in pharmacology. They are usually a summary of many drugs, referring to drugs used for allergies. In addition to histamine, other substances in the body may also be involved in allergic reactions. Different drugs are selected in different situations. For example, systemic allergic reactions will be treated first with epinephrine.

However, because we often use antihistamines when allergic symptoms occur in our daily lives, we mistakenly equate antihistamines with anti-allergic drugs. In fact, they just have some overlap.

What are antihistamines?

There are currently four types of histamine receptors found in the body, including H1, H2, H3 and H4. In order to help us relieve symptoms, antihistamines target these receptors, making histamine unable to work. Among them:

H1 antihistamines are the antihistamines we often discuss and use, mainly used for urticaria, allergic rhinitis, etc., including cetirizine, loratadine, etc.;

H2 antihistamines (such as cimetidine) are mainly used for peptic ulcer and gastroesophageal reflux disease;

Many H3 antihistamines are in clinical trials, and currently tilorixen is approved for narcolepsy;

H4 antihistamines are still in clinical trials.

Because H1 antihistamines have the most varieties and are the ones we usually come into contact with most often in treatment, today we will briefly learn about H1 antihistamines.

Note: Unless otherwise specified below, antihistamines refer to H1 antihistamines.

H1 antihistamines

H1 antihistamines are currently divided into two categories, first-generation H1 antihistamines and second-generation H1 antihistamines.

The first generation of H1 antihistamines , common ones include diphenhydramine, chlorpheniramine, etc.

Poor selectivity for H1 receptors (in addition to H1 receptors, it will also cause trouble for other receptors);

It is easy to pass through the blood-brain barrier (a structure between blood and brain tissue that can prevent some substances from entering the brain tissue and play a protective role), causing adverse reactions such as drowsiness, fatigue, and dizziness. It is a type of antihistamine with a sedative effect;

It may produce anticholinergic effects, which may cause blurred vision, dry eyes, nose and mouth, urinary retention, constipation, etc.

Multiple doses per day are generally required.

Therefore, first-generation antihistamines are no longer the first choice for urticaria and allergic rhinitis. However, in the case of motion sickness, first-generation antihistamines (such as diphenhydramine, dimenhydrinate, etc.) are preferred, while non-sedating second-generation antihistamines are not recommended.

Second-generation H1 antihistamines , common ones include cetirizine, loratadine, olopatadine, etc.

Highly selective for H1 receptors (basically only looking for H1 receptors, rarely bothering other receptors);

It is not easy to pass through the blood-brain barrier and has a weak sedative effect;

No obvious anticholinergic adverse reactions;

Generally , the drug can be administered once a day.

In general, it has fewer adverse reactions and is the recommended antihistamine for urticaria and allergic rhinitis. Second-generation antihistamines can also be used if obvious itching occurs after mosquito bites.

Cetirizine and loratadine

What exactly is the difference?

Cetirizine and loratadine are both commonly used second-generation antihistamines, but they belong to different types of compounds. However, there is not much difference in effectiveness and safety.

Some small sample studies have found that cetirizine is better than loratadine in improving symptoms in the treatment of allergic rhinitis and relieving mosquito bites, but it is more likely to cause sedation (such as drowsiness) than loratadine.

There is no data to indicate which drug is more effective for acute urticaria, but several studies on chronic urticaria suggest that cetirizine and levocetirizine may be slightly better than other drugs.

Cetirizine vs Loratadine, which one is better?

No one has been found to be optimal. Based on current evidence, when the indications are met, it can be used according to the doctor's advice, according to the applicable age and dosage (the medication recommendations for children, pregnant women and breastfeeding women can be found below).

In addition, due to individual differences in medication use, if one of the drugs is not effective or has obvious adverse reactions, another drug can be considered.

What should I pay attention to when using antihistamines?

Although antihistamines are used for many diseases, their use is a decision that weighs the pros and cons and needs to be combined with specific populations, diseases, etc.

When using antihistamines, we can pay attention to the following points:

1

Different diseases may have the same symptoms

The same symptoms that appear every time do not necessarily indicate the same disease. For example, allergic rhinitis and the common cold may both cause sneezing and runny nose.

If it is allergic rhinitis, you can use antihistamines to relieve symptoms. However, it is not recommended for the common cold, because antihistamines cannot effectively relieve the nasal symptoms of the common cold. So when symptoms appear, first analyze the cause and then consider medication.

2

The same disease may have different causes and pathogenesis

Antihistamines may be used for allergic rhinitis and urticaria.

For allergic rhinitis, although antihistamines often reduce itching, sneezing, and rhinorrhoea, they are not as effective as corticosteroid sprays for nasal congestion (nasal obstruction). Therefore, corticosteroids are recommended for patients with chronic symptoms, more severe symptoms, or if they have adverse reactions to antihistamines and prefer topical treatments.

Antihistamines are not always effective for urticaria. For example, for acute urticaria caused by Mycoplasma pneumoniae infection, antihistamines may not be effective. In this case, you may need to consider using anti-infective drugs such as azithromycin. Therefore, even if you have had the disease before, you should use the medicine according to the specific situation this time.

3

Second-generation antihistamines are generally safe and well tolerated

Although second-generation antihistamines generally have good safety and tolerability, the determination of the course of treatment and dosage needs to be comprehensively evaluated based on the type of disease and changes in the condition. Do not stop taking the medicine or increase the dosage at will during the process to avoid delaying treatment or increasing the chance of adverse reactions.

4

Medication recommendations for children

In addition to using it according to the applicable indications of the disease, children need to pay attention to the applicable age and dosage. For example, the applicable age and dosage of commonly used cetirizine and loratadine are:

Cetirizine:

≥6 years: 10 mg once a day

2 to 5 years: 5 mg once a day

6 months to 2 years: 2.5 mg, once a day

Loratadine:

≥6 years: 10 mg once a day

2 to 5 years: 5 mg once a day

Some medicine instructions may have some differences, such as:

Some instructions state that the minimum age for cetirizine is 1 year old, while others suggest that it should be used with caution from 6 months to 1 year old.

Some instructions for loratadine have different reference ages. The reference dosage is 10 mg once a day for children aged ≥12 years. For children aged 2-12 years, it depends on the weight: 10 mg once a day for children aged ≥30 kg and 5 mg once a day for children aged ≤30 kg. If both age and weight are considered, it is prudent to choose the lower dose.

When choosing dosage forms , you can choose appropriate dosage forms according to different age groups to improve children's compliance with medication. For example, liquid dosage forms can be preferred for young children, which are convenient for dosage measurement and administration, and are better than granules and dispersible tablets. In addition, young children have poor swallowing function, so capsules should be avoided.

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5

Medication recommendations for pregnant and lactating women:

Cetirizine or loratadine are the first choice during pregnancy and lactation. There is a large amount of data on the use of these two drugs in pregnant patients, and the results are reassuring. These two drugs are also rarely secreted into breast milk and usually do not cause sedation or feeding difficulties in infants.

Although the evidence-based database considers these two drugs to be relatively safe, some drug instructions mention that cetirizine is not recommended for use during pregnancy and breastfeeding, while loratadine usually advises caution when used during pregnancy and breastfeeding.

Because the scope of application of drugs approved in different countries and regions may be different, and the dosage of drugs for different diseases or for those with obvious renal and/or hepatic dysfunction may also be different, you can consult a doctor or pharmacist for specific medication questions.

References

[1]Tiligada E, Ennis M. Histamine pharmacology: from Sir Henry Dale to the 21st century. Br J Pharmacol. 2020 Feb;177(3):469-489. doi: 10.1111/bph.14524. Epub 2018 Dec 2. PMID: 30341770; PMCID: PMC7012941.

[2]Nayak AS, Berger WE, LaForce CF, Urdaneta ER, Patel MK, Franklin KB, Wu MM. Randomized, placebo-controlled study of cetirizine and loratadine in children with seasonal allergic rhinitis. Allergy Asthma Proc. 2017 May 1;38(3):222-230. doi: 10.2500/aap.2017.38.4050. PMID: 28441993.

[3]Karppinen A, Kautiainen H, Petman L, Burri P, Reunala T. Comparison of cetirizine, ebastine and loratadine in the treatment of immediate mosquito-bite allergy. Allergy. 2002 Jun;57(6):534-7. doi: 10.1034/j.1398-9995.2002.13201.x. PMID: 12028119.

[4] UpToDate: New-onset urticaria

[5] UpToDate: Treatment and prevention of the common cold in adults

[6] UpToDate: Common cold in children: Treatment and prevention

[7] UpToDate: Drug treatment of allergic rhinitis

[8] Part of the instructions for use of cetirizine and loratadine

[9] Zhou Pengxiang, Zhou Wei. Clinical practice guidelines for the rational use of oral H1 antihistamines in children (2022 edition)[J]. Chinese Journal of Evidence-Based Medicine, 2022, 12(22): 1365-1374.

[10]Drugs and Lactation Database (LactMed®): https://www.ncbi.nlm.nih.gov/books/NBK501922/

Planning and production

Source: YaeHer Health (ID: YaeHer)

Author: Hu Yu, pharmacist at Wuhan Puren Hospital

Reviewer: Tang Qin, Director and Researcher of the Science Popularization Department of the Chinese Medical Association

Editor: Zhong Yanping

Proofread by Xu Lailinlin

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