Advantages of Levocetirizine vs. Cetirizine
Levocetirizine offers minimal advantages over cetirizine, as it is the active R-enantiomer of cetirizine with comparable efficacy but potentially slightly better antipruritic effects, though possibly with increased sedation.
Pharmacological Differences
- Levocetirizine is the active R-enantiomer of cetirizine, which is a racemic mixture containing both levocetirizine and dextrocetirizine 1
- Levocetirizine has shown superior H1 receptor binding affinity compared to cetirizine 2
- Levocetirizine has a slower dissociation rate from the H1 receptor, making it an insurmountable antagonist 1
- The S-enantiomer (ucb 28557) has been found to be pharmacologically inactive in histamine-induced wheal and flare responses 3
Efficacy Comparison
- In histamine-induced wheal and flare studies, 2.5 mg of levocetirizine demonstrated comparable antihistaminic activity to 5 mg of cetirizine 3
- When comparing area under the curve measurements, levocetirizine was found to be superior to cetirizine in histamine-induced wheal and flare studies 3
- In chronic idiopathic urticaria, clinical efficacy between cetirizine and levocetirizine was comparable, with levocetirizine showing a marginal advantage in antipruritic effect 4
Sedation Profile
- Despite theoretical advantages, a randomized, double-blind, crossover, placebo-controlled trial found no significant difference in sedation between levocetirizine and cetirizine as measured by both the modified Epworth Sleepiness Scale and a Likert scale 5
- The British Association of Dermatologists' guidelines note that cetirizine may be sedating, especially at higher doses 6
- Patients who reported significant sedation with cetirizine in the past were able to tolerate both levocetirizine and cetirizine when given in a masked manner 5
Clinical Implications
- Guidelines do not specifically recommend one over the other for allergic rhinitis or urticaria 6
- Both medications should be used with caution in patients with renal impairment, with dose adjustments required 7
- For patients with a history of mild to moderate sedation with cetirizine, switching to levocetirizine is unlikely to provide a significantly different sedation profile 5
Practical Considerations
- The recommended dose of levocetirizine (5 mg once daily) is half that of cetirizine (10 mg once daily), reflecting that levocetirizine is the active enantiomer 1
- Both medications have similar pharmacokinetic half-lives (about 7 hours for levocetirizine) 1
- Both have negligible interactions with liver enzymes and are mainly excreted unchanged in urine 1
Caveats and Pitfalls
- Individual patient responses to antihistamines can vary significantly
- Patients who report sedation with one antihistamine may experience similar effects with others in the same class
- Cost considerations may influence choice between the two medications, as levocetirizine is often more expensive than generic cetirizine
- Neither medication has been conclusively shown to have superior efficacy compared to other second-generation antihistamines 6
In conclusion, while levocetirizine represents the active component of cetirizine with some theoretical pharmacological advantages, clinical studies show minimal practical differences between the two medications for most patients.