Nonsedating second-generation antihistaminics

It is virtually impossible to list all of the analogues, and several reviews have dealt with the structure-activity relationships (SAR) of antihistamines [6-9]. Together, these reviews provide an almost complete listing of the classic (first-generation) and the so-called nonsedating (second-generation) antihistamines. 

Although terfenadine was the first member of a new class of so-called nonsedating or second-generation antihistamines, several similar compounds were to follow. Terfenadine is pharmacologically an intriguing compound, as the chiral center neither plays a role in Ef blocking, nor is involved in receptor binding. It... 

The first-generation Hi antihistamines, also referred to as sedating antihistamines, and the second-generation antihistamines, the less or nonsedating antihistamines, are among the most frequently used oral medications for ocular allergies. Table 13-3 lists commonly used oral antihistamines and some of their important pharmacologic properties. 

Terfenadine, astemizole, loratadine, and cetirizine are second-generation antihistaminic agents that are relatively nonsedating. Other Hj-receptor antagonists currently undergoing clinical trials are azelastine, ebastine, and levocabastine. 

Histaminei (Hj) receptors mediate such actions as bron-choconstriction and the contraction of smooth muscles in the gastrointestinal tract. Ebastine is a histamine,-receptor blocker. Terfenadine, astemizole, loratadine, and certirizine are second-generation antihistamine agents that are relatively nonsedating. Other H,-receptor antagonists currently undergoing clinical trials are azelastine, ebastine, and levo-cabastine (see also Figures 34 and 59). 

Loratadine, a second-generation antihistamine, is well tolerated, nonsedating, and has not been associated with cardiac arrhythmias. 

Second-generation nonsedating antihistamines (e.g., loratadine) are not associated with erectile dysfunction. 

Acrivastine, an acidic congener of triprolidine in which a carboxylic acid-substituted chain has been attached, also is a second-generation, nonsedating antihistamine. Penetration of the blood-brain barrier is limited, and it is less sedating than triprolidine. It is used principally in a combination with a decongestant. 

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