Levocetirizine vs Cetirizine: what is the difference?
Cetirizine is a mix of two mirror-image forms and levocetirizine is the active one alone, so it works at about half the amount for a similar effect.
The same atoms; levocetirizine is one mirror-image form, cetirizine a mix of both.
Sources and notes
- The sentence under the titlefrom sourceMoleculeFinder comparison notesThe pair's answer line.
- The two drawingscomputedMoleculeFinder rule (RDKit MCS)Drawn the same way round on the skeleton they share; the amber marks where the two differ. Aligned; the same atoms, marked where their arrangement in space differs.
- The captionfrom sourceMoleculeFinder curated
- What is highlightedfrom sourceMoleculeFinder curatedOne line under each drawing, written from the atoms the amber marks.
- Structural similaritycomputedRDKit Morgan/Tanimoto1.00 of 1, a Morgan fingerprint Tanimoto coefficient. It measures shape, not effect.
Side by side
| Levocetirizine | Cetirizine | |
|---|---|---|
| Molecular weightCalculated PubChem | 388.9 g/molC21H25ClN2O3 | 388.9 g/molC21H25ClN2O3 |
| Hydrogen-bond donorsCalculated PubChem | 1 | 1 |
| Also sold asEditorial MoleculeFinder curated | Not recorded | Zyrtec |
| FamilyEditorial MoleculeFinder curated | Antihistamines | Over-the-counter medicines |
| Everyday groupEditorial MoleculeFinder curated | OTC medicine | OTC medicine |
| Chemical groupsCalculated Found by rule (RDKit) | Carboxylic Acids, Aromatics, Ethers, Halogenated | Carboxylic Acids, Aromatics, Ethers, Halogenated |
| Hazard labelReported ECHA via PubChem | Not recorded | Warning |
| The supplier-filed hazard label's signal word, not a statement about ordinary use. | ||
Sources and notes
- Molecular weightcomputedPubChemComputed from the structure; the formula is under each weight.
- Hydrogen-bond donorscomputedPubChemThe hydrogens on nitrogen or oxygen that each molecule can lend to a hydrogen bond, counted from its structure.
- Also sold asfrom sourceMoleculeFinder curated
- Familyfrom sourceMoleculeFinder curated
- Everyday groupfrom sourceMoleculeFinder curated
- Chemical groupscomputedFound by rule (RDKit)Each group is found in the structure by a chemical pattern.
- Hazard labelfrom sourceECHA via PubChem
- ECHAfrom sourceAttributionSource: European Chemicals Agency, echa.europa.eu.
- Identifiersfrom sourcePubChemPubChem CID 1549000 (Levocetirizine) and 2678 (Cetirizine).
In more detail
The two forms are mirror images of the same molecule. 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.
Sources and notes
- The paragraphfrom sourceMoleculeFinder comparison notes
Questions
- What is the difference between Levocetirizine and Cetirizine?
- Cetirizine is a mix of two mirror-image forms and levocetirizine is the active one alone, so it works at about half the amount for a similar effect.
- 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.
Sources and notes
- The answersfrom sourceMoleculeFinderThe first is the pair's answer line; the others are read off the table above.