Loratadine

Loratadine, commonly known by the brand name Claritin, is a medication belonging to the second-generation antihistamine class, used primarily to treat allergic conditions such as hay fever (allergic rhinitis) and hives (urticaria), including chronic idiopathic urticaria and other skin allergies. It is effective for both nasal symptoms like sneezing and a runny nose, as well as eye symptoms such as itching or burning. The drug is also available in a fixed-dose combination with pseudoephedrine, a nasal decongestant. Unlike older antihistamines, loratadine causes less sedation and psychomotor impairment because it penetrates the blood-brain barrier to a lesser degree, though some individuals may still experience sleepiness, dry mouth, or headache. It is largely free of antimuscarinic effects such as urinary retention or blurred vision. Serious side effects, including allergic reactions, seizures, and liver problems, are rare. Loratadine is considered safe during pregnancy (U.S. Category B) and is usually compatible with breastfeeding, but it is not recommended for children under two years old. The drug was patented in 1980 and brought to market in 1988 by Schering-Plough, which developed it as a nonsedating alternative to earlier antihistamines. It is on the World Health Organization's List of Essential Medicines and is available as a generic and over the counter in the United States. In 2023, it was the 105th most prescribed medication in the U.S., with over six million prescriptions. Loratadine is a tricyclic compound that acts as a selective inverse agonist at peripheral histamine H1 receptors. It is well absorbed orally, undergoes rapid first-pass metabolism in the liver via CYP3A4 and CYP2D6 enzymes, and has a biological half-life averaging eight hours, while its active metabolite, desloratadine, has a half-life of about 27 hours, providing a long-lasting effect. Drugs that inhibit CYP3A4, such as ketoconazole, erythromycin, cimetidine, and grapefruit compounds, can increase plasma levels of loratadine, but this does not typically cause clinically significant heart rhythm problems.