Loratadine
Second-Generation Antihistamine for Allergic Conditions: Effects, Indications and Notes
Loratadine is a second-generation antihistamine used for allergic complaints. Compared with first-generation antihistamines, loratadine causes substantially less sedation, i.e. fatigue and drowsiness. This makes it more compatible with everyday life and has established it as one of the most widely used anti-allergy agents worldwide.
The compound is available both with and without prescription in many countries, depending on dosage and formulation. Since the expiry of patent protection, loratadine has been available as a generic from various manufacturers, improving both availability and affordability.
Mechanism of Action
Loratadine acts as a selective antagonist at the H1 histamine receptor. Histamine is an endogenous mediator released from mast cells and basophilic granulocytes during allergic reactions and triggers typical complaints such as pruritus, sneezing, runny nose, watery eyes and swollen mucous membranes. Loratadine competitively blocks the H1 receptor, preventing histamine from binding there and exerting its effects.
An important difference from first-generation antihistamines lies in the limited ability of loratadine to cross the blood-brain barrier. As a result, the compound acts preferentially at peripheral H1 receptors and causes fewer central nervous system effects. The sedating effects typical of older antihistamines occur significantly less frequently with loratadine at therapeutic doses. First-generation antihistamines such as diphenhydramine or clemastine cross the blood-brain barrier readily and consequently cause fatigue and impaired reaction ability more frequently.
Loratadine is converted in the liver to the active metabolite desloratadine, which also has antihistaminic activity and is approved as an independent compound. Desloratadine is considered to be even less sedating than loratadine itself in some studies.
Indications
Allergic Rhinitis
The most common indication for loratadine is allergic rhinitis, commonly known as hay fever. Typical symptoms such as sneezing, nasal pruritus, runny or blocked nose and watery eyes can be relieved by loratadine. This applies to both seasonal allergies such as pollen allergy and perennial allergies such as house dust or animal hair allergy.
Loratadine is effective against the histamine-mediated acute symptoms of allergic rhinitis. Nasal congestion, which is more strongly mediated by other factors than histamine, may respond less well than sneezing and pruritus.
Chronic Idiopathic Urticaria
Loratadine is also used in chronic spontaneous urticaria (hives). This condition is characterised by recurrent wheals and pruritus on the skin. Second-generation antihistamines such as loratadine are considered first-line therapy for this condition. With an inadequate response to standard doses, the dose may be adjusted under medical supervision.
Allergic Conjunctivitis
In allergic conjunctivitis with pruritus and watery eyes, loratadine as a systemic antihistamine can contribute to symptom relief, often in combination with local eye drops.
Other Allergic Reactions
For other allergic skin manifestations with pruritus and insect-sting reactions, loratadine can be used for symptom relief, always considering the underlying cause and in consultation with a physician.
Formulations and Dosage
Loratadine is available as tablets, orally disintegrating tablets, syrup and capsules. The usual dosage for adults and children aged 12 years and over is 10 mg once daily. For younger children, weight-adapted dosages should be taken from the package leaflet or physician recommendation: children aged 2 to 12 years weighing less than 30 kg generally receive 5 mg daily.
The dose may be taken independently of meals. In persons with impaired renal or hepatic function, an adjusted dosage with a prolonged dosing interval may be necessary, as the metabolism of the compound may be slowed.
Notes on Administration
Although loratadine belongs to the less sedating antihistamines, fatigue can still occur in individual cases. Individual reaction to the compound can vary. Anyone who is sensitive to loratadine or belongs to the rare group who still experiences drowsiness should not drive vehicles or operate machinery until the individual response is clear.
Alcohol can enhance the sedating effect of antihistamines. Even though loratadine causes comparatively little sedation, caution is warranted with concurrent alcohol consumption. Excessive alcohol consumption should be avoided when taking loratadine.
Adverse Effects
Loratadine is generally well tolerated. Possible adverse effects include:
- Headache
- Fatigue (less common than with first-generation antihistamines)
- Dry mouth
- Nausea (occasional)
- Very rarely, allergic reactions to the compound itself
- Rarely, palpitations or cardiac arrhythmias
Drug Interactions
Loratadine is metabolised via hepatic enzymes (CYP3A4 and CYP2D6). Compounds that inhibit these enzymes may increase loratadine plasma levels. These include certain antifungals and macrolide antibiotics. These interactions are generally clinically less relevant for loratadine than for first-generation antihistamines; however, concurrent use with other medications should be discussed with the treating physician.
Comparison with Other Antihistamines
In addition to loratadine, other second-generation antihistamines are available, including cetirizine, fexofenadine and the loratadine metabolite desloratadine. All of these compounds have a similar activity profile but differ slightly in duration of action, metabolism and individual tolerability. Cetirizine is often considered somewhat more sedating than loratadine but shows good efficacy against pruritus in some patients. Fexofenadine crosses the blood-brain barrier even less easily than loratadine and is considered particularly non-sedating. The choice of the appropriate antihistamine should be made individually and in consultation with a physician.
Use in Pregnancy and Breastfeeding
The use of loratadine in pregnancy should be discussed with a physician. Available data do not show an increased risk of malformations with loratadine; however, the general principle of taking medications in pregnancy only when medically necessary applies. Loratadine passes into breast milk; medical advice should be sought if anti-allergic treatment is needed during lactation.
Frequently Asked Questions
How quickly does loratadine take effect?
Loratadine generally begins to act within one to three hours of intake. The maximum plasma concentration is reached after approximately one to two hours. Duration of action is 24 hours, which is why loratadine is taken once daily. For seasonal allergies, it is advisable to start loratadine before the pollen season begins, as prophylactic maintenance is more stable than as-needed use.
Can I take loratadine daily over a longer period?
Loratadine is designed for long-term use, particularly in chronic conditions such as perennial allergic rhinitis or chronic urticaria. With persistent complaints over more than a few weeks, medical evaluation is advisable, however, to clarify the cause of the allergic reaction and to consider further therapies if necessary. Allergen-specific immunotherapy (hyposensitisation) may reduce complaints in the long term when a proven allergy is present.
May I take loratadine and cetirizine simultaneously?
Simultaneous use of two antihistamines of the same generation is generally not useful and not recommended, as no additional benefit is to be expected but the risk of adverse effects may increase. If an anti-allergic treatment is not providing adequate relief, the treating physician should be consulted to discuss alternative or complementary therapies.