Fexofenadine

What it is

Fexofenadine is a second-generation antihistamine and the active metabolite of terfenadine; it blocks peripheral H1 receptors, cutting the itching, sneezing, nasal discharge and hives caused by histamine. It barely enters the brain, so it is among the least sedating of the antihistamines. It is used for allergic rhinitis and chronic urticaria.

Used for

• Allergy

What to know while taking it

It is taken without food, because a meal, especially a fatty one, reduces how much is absorbed. Fruit juices, in particular grapefruit, apple and orange, block the intestinal transporters that carry it into the body and can substantially lower its effect, so it is taken with water rather than juice. Antacids containing aluminium or magnesium interfere with absorption in a similar way and are best separated in time. Because it is largely eliminated unchanged, it interacts with fewer other medicines than most in its class.

When to see a doctor

Allergic symptoms that fail to improve on regular use, or hives that persist for weeks, warrant a doctor's assessment. Swelling of the face or throat, wheezing or difficulty breathing needs urgent medical care.

Worth knowing

• Do not take with fruit juice