Sedating antihistamines effect is related to
Patients suffering from seasonal allergic rhinitis and urticaria frequently use higher doses.
We therefore believe that warnings about antihistamines' possible adverse effects on driving and other potentially dangerous activities should not be waived for the 2nd generation drugs.
Their prescription-event monitoring study demonstrated that 2nd generation antihistamines differ in their potential to produce sedation.
The odds ratios for the incidence of sedation were 0.63 for fexofenadine, 2.79 for acrivastine and 3.53 for cetirizine compared with loratadine.
The 2nd generation antihistamines were less soluble in lipid and thus less readily penetrated the blood brain barrier.
When given to man in oral therapeutic doses terfenadine produced about 17% H1 receptor occupancy in the frontal lobe whereas the 1st generation antihistamine chlorpheneramine produced about 77% occupancy1.
BMJ 2000; 320: 1184-1186 4 O'Hanlon JF, Ramaekers JG.
Many sedating antihistamines do not require a doctor's prescription.However there is no reason to believe that all 'non- sedating' antihistamines possess exactly the same low tendency to cross the blood brain barrier.The study by Mann et al 3 nicely illustrates this point of view.That means you can control your symptoms with only 1 or 2 doses each day compared with older medications, which usually require doses every 4 to 6 hours to maintain their effectiveness.The newer antihistamines are available only by prescription.
Relationship between occupation of cerebral H1 receptors and sedative properties of antihistamines. Arzneimittelforschung 1982; 32: 1171-1173 3 Mann RD, Pearce GL, Dunn N, Shakir S.