Nonsedating second-generation

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. 

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

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). 

Second-generation Hj-receptor antagonists lack anticholinergic side effects and are described as nonsedating... 

The second-generation ( nonsedating ) Hj antagonists e.g., loratadine, cetirizine, and fexofenadine) are largely excluded from the brain when given in therapeutic doses because they do not cross the blood-brain barrier. An interesting and useful property of certain Hj antagonists is the capacity to counter motion sickness see Chapters 7 and 37). This effect was first observed with dimenhydrinate and subsequently with diphenhydramine (the active moiety of dimenhydrinate), various piperazine derivatives, and promethazine. 

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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