Levocetirizine vs Cetirizine: what is the difference?

How they differ

Cetirizine is a mixture of two mirror-image forms of the same molecule, and levocetirizine is just one of them isolated. The active half is levocetirizine, and the other half contributes very little H1 blocking, which is why levocetirizine works at about half the amount of cetirizine for a similar effect. Everything else about them is identical: same formula, same weight of 388.9, same receptor, same once-daily pattern. Whether isolating the active half produces a meaningfully better medicine or mainly a new patent is a debate that has followed several single-isomer products. Cetirizine is generally sold over the counter and levocetirizine varies by country.

Side by side

Structural similarity 1.00 of 1, computed as a Morgan fingerprint Tanimoto coefficient. It measures shape, not effect.

Common questions

What is the difference between Levocetirizine and Cetirizine?

Cetirizine is a mixture of two mirror-image forms of the same molecule, and levocetirizine is just one of them isolated. The active half is levocetirizine, and the other half contributes very little H1 blocking, which is why levocetirizine works at about half the amount of cetirizine for a similar effect. Everything else about them is identical: same formula, same weight of 388.9, same receptor, same once-daily pattern.

Do Levocetirizine and Cetirizine have the same formula?

Yes. Both are C21H25ClN2O3 at 388.9 g/mol. They are isomers: the same atoms arranged differently, which is why they behave differently despite weighing the same.