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Montelukast and levocetirizine are both medicines that work against allergic reactions, but the exact ways in which they do this differ. Conditions that either or both drugs are suitable for are those that are caused by oversensitive immune systems, such as pollen allergies. The function of both drugs is to interfere with an allergic reaction like asthma, and dampen down its effects. To do this, both montelukast and levocetirizine prevent certain molecules from binding to a receptor on cells, but the exact receptor is not the same for both.
Hay fever and other allergic conditions that are caused by inhalations of particles occur because the body launches an unnecessarily strong response to irritants like dust or pollen. At the core of the bodily response involved is the inflammation process. Normally, inflammation is useful for the body, as it helps to raise temperature and produce irritation at sites that are infected or exposed to dangerous foreign matter. In some people, however, inflammation occurs when it is unnecessary, and the lungs and nose, for instance, become inflamed for no good reason.
Inflammation in the lungs causes the airways to become smaller and narrower and this prevents air from getting in and out of the lungs. When the tissues of the nose are affected, the nose produces lots of thin mucus, and the eyes can also run. Some people experience a longterm allergy condition that is uncomfortable to live with, and so require special medication to keep the inflammation under control.
Both montelukast and levocetirizine act on the body to regulate an overly aggressive immune response. They do this by blocking a step in the inflammation cascade, which prevents the inflammation from getting worse, or can reduce the inflammation. Although for both montelukast and levocetirizine the target step involves a receptor on the outside of a cell, the specific receptor is different for each.
Levocetirizine is a medicine that is very closely related to another common allergy medicine called cetirizine. Its target cell receptor is peripheral H1-receptor. This receptor plays a role in the recognition of inflammation signals called histamines, and the medicine blocks the receptors from identifying instructions to continue the inflammation process.
On the other hand, montelukast also interferes with signal reception on cells. The particular cell receptor it affects is cysteinyl leukotriene receptor, which also forms part of the inflammation response, but in a different way to the levocetirizine target. Both montelukast and levocetirizine can be absorbed through the gastrointestinal tract, and as they work in parallel ways, are available together in some allergy medications.