Xyzal -- "Son" of Zyrtec

Xyzal (levocetirizine) is the new levo isomer derivative of Zyrtec (cetirizine) which will be marketed and sold similarly to:

Claritin --> Clarinex
Prevacid --> Nexium

On 5/29/2007, the FDA approved Xyzal once-daily tablets for relief of symptoms of seasonal and perennial allergic rhinitis and chronic idiopathic urticaria in adults and children 6 years of age and older.

Sedation side effects

Second generation antihistamines have greater H1-receptor specificity than first generation. Cetirizine, loratadine, and desloratadine have dose-related sedation which is not detectable in the FDA approved doses. Fexofenadine has no greater sedative effect than placebo in every dose studied.

F
Fexofenadine
Free of sedation at any dose

It is probably safer to use fexofenadine (Allegra) in pilots and operators of vehicles and heavy machinery rather than the other second generation antihistamines currently available on the market.

References:

Zyrtec Looks in Mirror and Sees Xyzal. WSJ Health Blog.
Antihistamine implicated in a helicopter crash
Allergic Rhinitis. Allergy Cases.
Image source: Wikipedia, GNU Free Documentation License.

Related:

The Best Antihistamines for Sneezing and Nasal Congestion. Paul Enright, MD, 04/2008.
Comparison of the sedating effects of levocetirizine and cetirizine: no difference http://goo.gl/lGu3Q