Loratadine is an oral antihistamine used to relieve symptoms of allergy, particularly allergic rhinitis and urticaria (hives). It blocks the effects of histamine and belongs to the group of less-sedating antihistamines commonly described as second-generation agents. It is sold under brand names including Claritin and Alavert. (medlineplus.gov)
Mechanism of action
Loratadine is a tricyclic drug with selective activity at peripheral histamine receptors. By blocking histamine’s effects at these receptors, it reduces histamine-mediated allergic symptoms. At labeled doses, most people do not experience clinically significant sedation or anticholinergic effects, although drowsiness remains possible. (medicines.org.uk)
In studies measuring histamine-induced skin wheals, antihistamine activity appeared within one to three hours, peaked at eight to twelve hours, and lasted more than 24 hours. These measurements describe a pharmacological response rather than a guaranteed timetable for symptom relief in every individual. (medicines.org.uk)
Clinical uses and formulations
Loratadine relieves sneezing, a runny nose, itching of the nose or throat, and itchy or watery eyes associated with hay fever and other upper respiratory allergies. It is also used to reduce the itching and redness associated with hives. (medlineplus.gov)
Available oral formulations include conventional tablets, chewable tablets, rapidly disintegrating tablets, capsules, and liquids. Administration is generally once daily, with or without food. Products such as Claritin-D contain loratadine together with pseudoephedrine and are combination medicines rather than loratadine alone. (medlineplus.gov)
The United States label for Claritin 10 mg tablets specifies once-daily administration for adults and children aged six years and older. Pediatric age limits and suitable formulations are product-specific; the tablet label treats younger children separately. (dailymed.nlm.nih.gov)
Metabolism and elimination
After oral administration, loratadine is rapidly absorbed and undergoes extensive first-pass metabolism, mainly through the enzymes CYP3A4 and CYP2D6. Its principal active metabolite, desloratadine, accounts for a substantial part of its clinical effect. (medicines.org.uk)
Mean elimination half-lives reported in healthy adults are approximately 8.4 hours for loratadine and 28 hours for desloratadine, with considerable variation between individuals. Elimination occurs through urine and feces, predominantly as metabolites. Liver impairment can increase exposure and prolong elimination. (medicines.org.uk)
Adverse effects and interactions
Reported adverse effects include drowsiness, headache, increased appetite, and insomnia. Product information also lists very rare hypersensitivity reactions, including anaphylaxis, and reports of palpitations and abnormal liver function. Overdose has been associated with drowsiness, a rapid heart rate, and headache. (medicines.org.uk)
Drugs that inhibit CYP3A4 or CYP2D6 can raise loratadine concentrations. Controlled studies with ketoconazole, erythromycin, and cimetidine found increased concentrations without clinically significant changes, including electrocardiographic changes. Loratadine can also suppress reactions in allergy skin testing. (medicines.org.uk)
The United States tablet label identifies previous allergic reactions to the product or its ingredients as a contraindication and includes precautions concerning liver or kidney disease, pregnancy, and breastfeeding. Its “non-drowsy” description does not mean that drowsiness is impossible, particularly when more than the labeled amount is taken. (dailymed.nlm.nih.gov)
Regulatory history
The United States Food and Drug Administration approved Claritin tablets on April 12, 1993. Their switch from prescription-only to over-the-counter status was approved on November 12, 2002. Subsequent approvals covered additional formulations and combination products. (accessdata.fda.gov)
References
- Loratadine: MedlinePlus Drug Informationmedlineplus.gov
- Antihistamines for allergies: MedlinePlus Medical Encyclopediamedlineplus.gov
- Loratadine 10 mg Tablets — Summary of Product Characteristicsmedicines.org.uk
- Loratadine 10 mg Tablets (P) — Summary of Product Characteristicsmedicines.org.uk
- DailyMed — CLARITIN- loratadine tabletdailymed.nlm.nih.gov
- FDA Medical Review: Application 021891accessdata.fda.gov