Cetirizine, Oxatomide, Ketotifen and Placebo: Pharmacological Evaluation of their Respective Anti-H1-Histamine, Antipruritic and Sedating Effects

Sedation and antihistamines: a review of inter-drug differences using proportional impairment ratios

The use of antihistamines (AHs) has until recently been associated with a number of undesirable side effects, the most troublesome of which is sedation. There are two aspects to sedation. The first, an objectively determined measure based on the results of psychometric tests from controlled trials, and the second, the subject's response to the administration of a drug. Since AHs are largely used in ambulant patients, a complete evaluation of sedation should be performed through standardised objective and subjective tests, shown to be sensitive to the central effects of AHs.An extensive review of the literature identified 76 studies of H(1) receptor antagonists in healthy volunteers, in which assessment of sedation was the primary objective. Results from studies published in peer-reviewed journals which employed a placebo condition as well as a positive internal control using a crossover design were analysed to determine the extent to which a particular antihistamine produced impairments on a battery of psychometric tests. The impairment index for each antihistamine was calculated and subsequently compared with the impairment index obtained for all other AHs.The calculation of this proportional impairment ratio enabled the sedative potential of an individual antihistamine to be identified relative to all other AHs and thus allowed the ranking of AHs with respect to their ability to cause impairments of cognitive and psychomotor function.Findings from this review clearly demonstrate that there are distinct classes of AHs with respect to their ability to impair cognitive function and psychomotor performance. Copyright 2000 John Wiley & Sons, Ltd.

Antihistamines: models to assess sedative properties, assessment of sedation, safety and other side-effects

Behavioural changes are produced by any drug that enters the central nervous system. These psychoactive effects include changes in alertness, concentration, attention, memory, cognition, psychomotor accuracy, skilled performance and affect. Changes in psychological performance may affect the safety of both the individuals taking the drug and of those people coming into contact with them. The aims of psychopharmacological performance tests are to describe the nature, extent and severity of these changes and identify drugs without deleterious effects upon performance. Use of traditional antihistamines has until recently been associated with a number of undesirable side-effects, the most troublesome of which is sedation. There are two aspects to sedation. Firstly, an objectively determined one based on the results of psychometric tests from controlled trials and secondly, the subjects response to the administration of a drug. Although the second generation of antihistamines have a much more favourable therapeutic index, use of these agents has also been reported to cause varying degrees of sedation. As antihistamines are largely used by ambulant patients, a complete evaluation of sedation should be performed through standardized objective tests, shown to be sensitive to the central effects of antihistamines as well as reliable ratings of subjective experiences. An extensive review of the literature has identified a number of tests which appear to be sensitive to the central effects of antihistamines. These include tests of psychomotor performance, sensori-motor co-ordination speed, information processing, sensory skills as well as physiological measures and subjective rating scales. Using this battery of cognitive and psychomotor tests, it is evident that only a very limited number of antihistamines can claim to be virtually free of both objective and subjective sedative effects, although the second generation of antihistamines are generally less impairing than the original ones; when prescribed at their recommended doses.

Agonist-antagonist interactions in the skin: comparison of effects of loratadine and cetirizine on skin vascular responses to prick tests with histamine and substance P

The skin vascular responses (weal, flare, blood flow measurements) elicited by intradermal administration by pricking of histamine (HS) and substance P (SP) were evaluated 6 h after a single intake of anti-H1 agents displaying different activity profile on skin tests at currently recommended dosages (loratadine 10 mg, cetirizine 10 mg) as compared to placebo (P). The weal and flare response and the increases of blood flow occurring in the usual flare area after HS and SP were almost completely abolished by cetirizine. Inhibition of HS- and SP-induced weal and flare reactions was less marked after loratadine and blood flow in the expanding flare after HS and SP showed significant fluctuations over time. In view of the present results and of data obtained in previous experiments with intradermal injection of agonists, we hypothesize that mode of administration of agonists significantly influences the size of the residual weal after anti-H1 agents. We demonstrate that SP weals induced by pricking are largely inhibited by a potent H1 blockade which supports the view that this phenomenon, as well as the SP-flare, is due to SP-induced histamine liberation. We also, for the first time, report on fluctuations recorded at the edge of the developing flare with laser Doppler flowmetry early after prick testing with a weak H1 blockade. This opens up new avenues in dynamically testing H1-receptor occupancy in vivo and in situ in human skin.