Though both loratadine and cetirizine are types of antihistamines, they are each a different chemical compound that treats the symptoms of allergies in different ways. Both of these drugs are given for the same types of allergies, and they are both effective against sneezing, nose itchiness, and watery eyes and ineffective against symptoms such as hives and systemic allergic reactions. Despite the similarities in the effects of these drugs, their chemical compositions are different and as a result, they have different effects on patients who take them.
Molecularly, these substances are structured in different ways. Loratadine is made up of 22 carbon atoms, 23 hydrogen atoms, two nitrogen atoms, two oxygen atoms and a chlorine atom. These atoms are arranged into a molecule that has a number of different branches. Cetirizine is made up of 21 carbon atoms, 25 hydrogen atoms, three oxygen atoms, two nitrogen atoms and one chlorine atom that are arranged into a long chain and connected to two molecules of hydrochloride. Though the building blocks are similar, the arrangement of these molecules allows them to fight allergy symptoms in different ways.
One of the main differences between loratadine and cetirizine are the types of side effects that patients may experience when taking them. While dry mouth and gastrointestinal discomfort are seen with the use of both of these medications, loratadine is also known to cause headaches, mouth sores, nervousness, and restlessness. Cetirizine, on the other hand, can cause drowsiness that may be severe in some patients. It is also possible for patients taking cetirizine to experience difficulty breathing, a side effect not usually seen in patients taking loratadine unless the patient is going into anaphylaxis.
Another difference between loratadine and cetirizine is the way each drug can be administered. Adults are usually given a dose of 10 milligrams once per day of either of these medications, while children over the age of two are often given half that amount. There is no established dosage of loratadine for children younger than two, whereas children between the ages of six months and two years can safely take 2.5 milligrams of cetirizine.
The long-term effects of high doses of loratadine and cetirizine are also different. In laboratory tests, cetirizine did not increase the risk of cancer or decrease fertility, even when given at doses well above the recommended maximum dose. Extremely high doses of loratadine did lead to an increased cancer risk, however, as well as a decrease in male fertility.