Inhibition of the histamine‐induced weal and flare response: a valid surrogate measure for antihistamine clinical efficacy?

Histamine plays a central role in allergic responses. Inhibition of the weal and flare response to histamine is a traditional pharmacodynamic tool to measure the activity of H(1)-receptor antagonists. The time course and duration of cutaneous weal and flare inhibition are often used as surrogate measures of clinical efficacy. Pharmacodynamic differences among antihistamines are often interpreted to indicate differences in clinical efficacy. A systematic review of literature from 1980 to 2006 regarding the histamine induced weal and flare was undertaken. Search terms included 'histamine', 'skin test', 'weal', 'flare', and 'antihistamine'; retrieved articles were searched for relevant studies not identified initially. Data from human studies on the inhibition of the weal and flare by second-generation antihistamines were extracted and assessed. A literature search from 1980 to 2006 was undertaken for comparative studies of second-generation antihistamines in the clinical settings of allergic rhinitis (AR) and chronic idiopathic urticaria; data extracted from these studies underwent systematic review. Differences were noted among second-generation antihistamines in terms of their ability to inhibit the histamine-induced weal and flare. Corresponding differences in terms of clinical efficacy in AR and chronic urticaria were not identified following a systematic review. The reasons for the disconnect between pharmacodynamic effects and clinical efficacy may include differences between the route and concentration of histamine, the involvement of mediators other than histamine in the allergic response, and the short time course of pharmacodynamic studies. The histamine-induced weal and flare response is a pharmacodynamic test that should not be used to compare the clinical efficacy of different antihistamines, and is not an adequate alternative to clinical end-point assessments in AR or chronic idiopathic urticaria.     

Skin responses to intradermal histamine and leukotrienes C4, D4, and E4 in patients with chronic idiopathic urticaria and in normal subjects

Mast cell inflammatory mediators, such as histamine, and newly formed compounds, such as the leukotrienes, cause wheal and flare when they are injected intradermally into normal subjects and may therefore play a role in the formation of urticaria. The effects of intradermal injections (50 microliters) of six different concentrations of histamine (range, 3.3 x 10(-4) to 3.3 x 10(-9) mol/L) and the leukotrienes C4, D4, and E4 (range, 2 x 10(-4) to 2 x 10(-9) mol/L) have been compared in 10 normal subjects and in 10 patients with chronic idiopathic urticaria. Wheal-and-flare sizes were measured at timed intervals up to 4 hours, and area under the curve for each response over time was calculated. There were no significant differences in leukotriene-induced responses between groups. Maximum sizes of histamine-induced wheal and flare were similar in each group of subjects. There were, however, significant increases in mean areas under the response curve of histamine wheal and flare in the patients with urticaria (wheal, p less than 0.001; flare, p less than 0.001; analysis of variance). These findings demonstrate a prolongation of skin responses to histamine in patients with urticaria and suggest an impaired clearance of histamine (or other vasoactive agents released by histamine) from the skin of these patients.     

A randomized, double-blind, crossover comparison among cetirizine, levocetirizine, and ucb 28557 on histamine-induced cutaneous responses in healthy adult volunteers

BACKGROUND: Cetirizine is a highly efficacious and long-acting second-generation H1-receptor antagonist for the treatment of allergic diseases, such as allergic rhinitis and chronic idiopathic urticaria, in adults and children. Pharmacologic studies have demonstrated that cetirizine, a racemate mixture composed of equal amounts of two enantiomers, does not undergo hepatic metabolism to any significant level. The enantiomers are excreted mainly unchanged, predominantly in the urine and to a lesser extent in the faeces. METHODS: The pharmacologic activity and potency of the two enantiomers of cetirizine in the management of allergic skin conditions were investigated by studying the effect of treatment with 5.0 mg cetirizine; 2.5 mg levocetirizine, the (R)-enantiomer; and 2.5 mg ucb 28557, the (S)-enantiomer, on histamine-induced wheal and flare response in 18 healthy volunteers. Each treatment was administered as a single oral dose in randomized, double-blind, and crossover manner, and the efficacy of treatment was assessed over a period of 32 h, as per cent inhibition of the histamine-induced wheal and flare areas before treatment. Blood and urine samples were collected in a time-dependent manner and analyzed for the total amounts of each study drug, to elucidate their pharmacokinetic profiles. RESULTS: Both cetirizine and levocetirizine caused a marked inhibition of histamine-induced wheal and flare, whereas ucb 28557 was inactive in this model. Inhibition of the wheal response observed for cetirizine and levocetirizine was apparent by 1 h after dosage and lasted for mean durations of 24.4 and 28.4 h, respectively. In addition, the response for cetirizine and levocetirizine became maximal by 6 h after treatment, rising to 79.5% and 83.8%. Similarly, cetirizine and levocetirizine also markedly inhibited the histamine-induced flare response. This effect was evident for both drugs by 1 h after dosage and lasted over a mean period of 28.4 and 26.0 h, respectively, for cetirizine and levocetirizine. The inhibitory effect of these compounds on histamine-induced flare response was also maximal by approximately 6 h after dosage, peaking at 88.5%) and 83.6%, respectively. Statistical evaluation showed that cetirizine and levocetirizine were equivalent for maximum inhibition of histamine-induced wheal and flare. However, levocetirizine was found to be superior to cetirizine when area under the curve was compared. In contrast, ucb 28557 was not found to inhibit histamine-induced wheal and flare responses at any time during the study period. Plasma concentrations of levocetirizine were found to be approximately double those of ucb 28557 at 4 and 8 h after dosing, and 50-60% of the drugs were excreted unchanged in urine over a period of 32 h. CONCLUSIONS: The finding that, in this model, levocetirizine 2.5 mg has comparable antihistaminic activity to cetirizine 5 mg, whereas its other enantiomer ucb 28557 has no pharmacodynamic effect, suggests that the antihistaminic properties of cetirizine observed in the management of allergic skin conditions are likely to be attributable to levocetirizine.     

Comparison of the effects in the nose and skin of a single dose of desloratadine and levocetirizine over 24 hours

BACKGROUND: Desloratadine (DL) and levocetirizine (LCZ) are the newest commercialized antihistamines. Pharmacokinetics, pharmacodynamics and clinical data are available for both drugs, but there is to date no direct comparison involving the nose and skin at the same time. We compared the effects of a single dose of the two drugs in the nose and skin over 24 h. METHODS: Twenty-three patients with symptomatic allergic rhinitis were enrolled in a randomized double-blind crossover administration of DL and LCZ. The histamine-induced wheal and flare was measured at baseline and 2 and 24 h after dosing. A reflective total symptom score (rTSS) for the previous 24 h was assessed before and after each dose. An instant symptom score was also measured at various time points after each drug. RESULTS: LCZ provided greater inhibition of the flare at 2 h (p = 0.05) and at 24 h (p = 0.007) and greater inhibition of the wheal only at 2 h (p = 0.02). The decrease in wheal and flare was significant versus baseline (p = 0.007) with both drugs. The rTSS of the previous 24 h decreased significantly with both LCZ (11.53 vs. 8.0; p < 0.05) and DL (11.3 vs. 7.9; p < 0.05). The instant TSS progressively decreased in parallel with both drugs, but a difference in favor of LCZ was seen 2 h after dosing. CONCLUSIONS: Single doses of DL and LCZ had a comparable effect on nasal symptoms, but LCZ was faster and displayed a greater effect on histamine wheal.     

Comparative activity of cetirizine and desloratadine on histamine-induced wheal-and-flare responses during 24 hours.

BACKGROUND: Cetirizine and desloratadine are antihistamines active in the treatment of symptoms associated with seasonal allergic rhinitis and chronic urticaria. OBJECTIVE: To compare the antihistamine activity of desloratadine, the active metabolite of loratadine, with that of cetirizine in the skin wheal-and-flare responses during 24 hours. METHODS: This was a double-blind, randomized, placebo-controlled, single oral dose, crossover study. Skin reaction to histamine (100 mg/mL), administered by prick tests, was measured by the wheal and flare surface areas for 24 hours (before treatment and at 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and 24 hours). Eighteen healthy volunteers (mean age, 33.9 years; 13 women) participated in this study. The areas under the curves of the wheal-and-flare responses as a function of time (primary efficacy variables) were compared using analysis of variance. RESULTS: A highly significant overall treatment effect (P < .001) was detected for wheal and flare inhibition, with the activity of cetirizine and desloratadine significantly superior to that of placebo (P < .001). In addition, the activity of cetirizine was significantly superior to that of desloratadine (P < .001). With desloratadine, only 3 of the 18 subjects achieved a wheal inhibition of at least 70%, occurring between 2 and 4 hours, whereas all subjects using cetirizine reached a wheal inhibition of at least 70% between 0.5 and 3 hours (median time, 1.7 hours). The difference between the 2 active drugs was highly significant (P < .001). The median duration of wheal inhibition of at least 70% was zero with placebo and desloratadine and was 21.9 hours with cetirizine (P < .001). No serious adverse events were reported, and no subject withdrew from the study due to an adverse event. CONCLUSION: Cetirizine was associated with significantly greater suppression of skin reactivity to histamine compared with desloratadine during 24 hours after a single dose, with a consistent duration of action for cetirizine, as previously reported.     

Mizolastine: antihistaminic activity from preclinical data to clinical evaluation

Mizolastine, a new H₁-receptor antagonist, is highly selective for histamine H₁ receptors and has no anticholinergic, antiadrenergic, or antiserotonin activity. It is rapidly absorbed after oral ingestion, with peak plasma concentrations occurring at 1.5 h. The distribution and terminal elimination half-life values are 2 and 13 h, respectively, in healthy young adult volunteers. Half-life values are longer in the elderly and in subjects with chronic renal insufficiency; however, the differences are not large enough to be clinically relevant or to necessitate a dose adjustment in these populations.
  Mizolastine produces prompt, sustained, peripheral blockade of histamine H₁ receptors in the skin. Suppression of the histamine-induced wheal and flare begins 40–60 min after ingestion of a 10-mg dose, peaks at 3–4 h, lasts for at least 24 h, and does not decrease during regular once-daily dosing. The amount of wheal suppression is comparable to that produced by other leading new H₁-receptor antagonists.
  These pharmacokinetic and pharmacodynamic studies of mizolastine provide its clinical pharmacology 'signature'. They also provide the scientific rationale for recommending a once-daily 10-mg dose and suggest that the efficacy and effectiveness of mizolastine will be widely confirmed in allergic disorders, especially rhinitis and urticaria.     

Suplatast tosilate inhibits eosinophil production and recruitment into the skin in murine contact sensitivity

Antiallergic drugs and antihistamines have been widely used for controlling mucosal allergic diseases in which eosinophilia is prominent. Although H1-receptor antagonists are effective for treating histamine-induced wheal and itch in urticaria, the effects of antihistamines and antiallergic agents on other eosinophilic skin diseases remain to be determined. We investigated the effects of oral administration of antiallergic drugs and antihistamines, such as suplatast tosilate, emedastine difumarate, and azelastine hydrochloride, on a novel murine model of eosinophilia in contact sensitivity to picryl chloride. Among the drugs tested, only suplatast tosilate remarkably inhibited blood and tissue eosinophilia and the ear swelling responses. The inhibitory effects on eosinophilia seemed to be mediated by the suppression of IL-5 production in spleen cells during eosinophil development, while the effects on the ear swelling response seemed to be mediated by suppression of IL-4 production in immune lymph node cells in the efferent phase. Suplatast tosilate may effectively treat eosinophilic skin diseases in which Th2-cell-derived cytokines are predominant.     

The effect of ascorbic acid on cutaneous and nasal response to histamine and allergen

The effect of ascorbic acid (AA) on the skin wheal and flare response to histamine and allergen and on the nasal response to allergen was evaluated in eight adults with seasonal allergic rhinitis. The above parameters were measured after 3 days of AA administration (2 gm/day) and again after 3 days of a similar-appearing lactose placebo. An additional study was conducted in which six subjects took 0 (placebo), 1, 2, and 4 gm/day of AA to determine the dose-response effect of AA on histamine skin tests. Overall there was no difference in skin or nasal reactivity between AA and placebo regimens. The findings in this study suggest that AA in relatively high doses would have no beneficial effects on symptoms resulting from allergen exposure and that AA in doses of up to 4 gm/day will not suppress the histamine skin response.     

Clinical advantages of dual activity in urticaria

Urticaria is a common disorder that adversely affects quality of life; work-related and recreational activities are restricted, while rest, sleep, and emotions are seriously disturbed in a significant proportion of patients. The pathogenic mechanisms vary, but cutaneous mast-cell activation with release of histamine and other vasoactive or proinflammatory mediators is thought to be the final common pathway for lesion induction in most cases. A subsequent, but incompletely understood, late-phase allergic reaction seems to prolong the inflammatory process, particularly in certain chronic forms of the disorder. Although histamine is considered an important mediator of urticaria, additional substances, including the cysteinyl leukotrienes (LTs), are putative mediators of the immediate urticarial responses and the inflammatory events that follow in some types of urticaria. A second-generation antihistamine, mizolastine, which exhibits dual activity with selective H₁-receptor antagonism and, as shown in animal studies, anti-5-lipoxygenase activity, represents an advance in the treatment of urticaria. It has rapid, potent and sustained action. At the recommended 10-mg dose, mizolastine suppresses the histamine-induced wheal reaction as early as 1 h after oral administration. Compared to placebo, mizolastine significantly reduces overall patient discomfort and pruritus in patients with chronic idiopathic urticaria. Double-blind, placebo-controlled studies have also shown mizolastine to be at least as effective as other second-generation antihistamines. Furthermore, with long-term use of mizolastine over 1 year, a reduction in pruritus and the number of urticarial episodes was maintained with no evidence of tachyphylaxis or tolerance. Mizolastine has also been shown to be an effective treatment for cold-induced urticaria, causing significant delay in the whealing response to the ice-cube test and also reducing the wheal diameter.     

A double-blind, randomized, single-dose, crossover comparison of levocetirizine with ebastine, fexofenadine, loratadine, mizolastine, and placebo: suppression of histamine-induced wheal-and-flare response during 24 hours in healthy male subjects.

BACKGROUND: Levocetirizine is the active enantiomer of cetirizine, a potent drug with little metabolism widely used for allergic rhinitis and urticaria. OBJECTIVE: This study compares the potency, consistency, onset, and duration of action of levocetirizine with other popular antihistamines. METHODS: Levocetirizine 5 mg, ebastine 10 mg, fexofenadine 180 mg, loratadine 10 mg, mizolastine 10 mg, or placebo in single doses were given to 18 healthy male volunteers in a double-blind, crossover, randomized fashion. Wheal-and-flare responses to epicutaneous histamine dihydrochloride (100 mg/mL) challenge were measured at 0, 0.5, 1, 2, 4, 6, 8, 10, 12, and 24 hours after each dose. RESULTS: The overall effect of each drug was evaluated by the area under the curve (0 to 24 hours). Levocetirizine was the most potent and consistently effective drug for inhibiting the histamine-induced wheal-and-flare surface areas. Ebastine, fexofenadine, and mizolastine ranked next and had almost identical effects for inhibiting the wheal. Loratadine was the least potent drug. Levocetirizine, fexofenadine, and mizolastine inhibited the wheal-and-flare response after 1 hour and reached their peak for inhibition after 4 hours. Ebastine and loratadine could be distinguished from placebo only after 4 hours. After treatment with levocetirizine, all 18 subjects had >95% inhibition of the wheal response at one timepoint. Fexofenadine, mizolastine, and ebastine were inhibitory in declining order. All treatments were considered safe and well tolerated. CONCLUSIONS: Levocetirizine, the active enantiomer of cetirizine, is more potent and consistent than other popular H1 antihistamines for blocking the cutaneous response to histamine. These findings may predict the efficacy of this drug in treating allergic disorders.     

Lack of subsensitivity to mizolastine over 8-week treatment

Mizolastine is a new, nonsedating antihistamine providing satisfactory symptom relief in allergic rhinitis and urticaria. The purpose of this study was to use the wheal and flare skin reactions model to assess the maintenance of the pharmacodynamic effect of mizolastine, administered for 2 months. This double-blind, parallel-group study involved 60 atopic patients randomly allocated, after a J-week placebo run-in, to once-daily 10 mg mizolastine ( n =29) or placebo ( n =31) groups. Treatment continued for 8 weeks. Pricks tests were performed in duplicate with histamine chlorhydrate (10 mg/ml), codeine phosphate (9%), and five increasing concentrations (1–500 reactivity index/ml) of standardized allergen extracts (grass pollen or mites) at days 0,7,28,42, and 56. After 7 days of treatment, inhibition of histamine-induced wheal was -76% and +20%, respectively, with mizolastine and placebo ( P =0.0001), in comparison with baseline; inhibition of flare was -86% and +5%, respectively, with mizolastine and placebo ( P =0.0001). Suppression was maintained to a similar extent throughout the study. Results were consistent between histamine-, codeine-, and allergen-induced tests. Safety was satisfactory in both groups. This study confirms mizolastine as a potent antihistamine which does not induce subsensitivity when taken for 81 weeks, and which can be safely recommended in allergic conditions.     

Wheal-and-flare reactions induced by allergen and histamine: evaluation of blood flow with laser Doppler flowmetry

Dermal blood flow was evaluated after skin prick test with histamine and allergen in six patients with seasonal allergic rhinitis. Blood flow was registered continuously for 60 minutes after the test procedure with laser doppler flowmetry, which allows noninvasive measurements. Blood flow was measured close to the skin test in the wheal obtained, and at a greater distance from the prick in the flare reaction. Tests were performed with preloaded skin test needles with histamine and the appropriate allergen freeze-dried on the point of the lancet, as well as with the appropriate negative control. The prick test procedure, by itself, induced a transient increase in blood flow that was normalized again after 9 minutes for the closest measurement. Histamine induced a rapid increase in blood flow in both the flare and wheal reaction that was normalized after about 45 minutes. The increase was significantly higher in the flare compared to the wheal for the time points from 6 1/2 to 13 minutes. Allergen induced a similar increase in blood flow. However, the increase was not noticeable until 2 1/2 minutes after the allergen application and was not completely abolished within 60 minutes. Furthermore, the difference between the flare and wheal reaction, with the higher values for the flare reaction, was present for a longer period of time than for the equivalent histamine measurements. In conclusion, laser doppler flowmetry appears useful for continuous evaluation of vascular changes induced at skin prick tests.(ABSTRACT TRUNCATED AT 250 WORDS)     

Histamine is released in the wheal but not the flare following challenge of human skin in vivo: a microdialysis study

Background The mediator mechanisms of the cutaneous wheal and flare response, which underlies allergic skin and urticarial conditions, are controversial. The wheal results primarily from a direct effect of histamine on the local vascular bed, but to what extent does histamine diffuse within the wheal? The flare is neurogenic in origin, being disseminated within the dermis by axon reflexes, but do the neuropeptides released from the nerve endings cause the vasodilatation directly or do they induce the further release of histamine which then transduces the fiare? Objective We have addressed these questions by inserting 216 μm diameter microdialysis fibres into the dermis within the different areas of the wheal and flare to monitor changes in histamine levels provoked by intradermal injections of histamine, allergen, codeine and substance P. Twenty-one subjects participated in the investigations. Results The histamine concentration in unprovoked skin was 10.5 ± 0.6 nM. As the dialysis efficacy was 50%, this equates to tissue concentrations of 20 nM. All provicants released large amounts of histamine at the injection site, maximum histamine levels being 337–1293 nM. Diffusion of histamine within the wheai was poor, levels at 2.3 mm and 3.7 mm from the site of injection being 4–22% and 0.2–3.7% respectively of those 1 mm from the injection site. No increased histamine levels were detected in the flare with any provicant. Atraumatic delivery to the skin of histamine in infusion concentrations of 30–10000 nM caused concentration-related effects, at least 100 nM being necessary to induce a significant increase in skin blood flow, a threshold of 300–1000 being required to stimulate a visible flare and a measurable erythema, and 3000–10000 nM being the minimum for induction of a wheal. Thus the skin blood vessels and nerves are responsive to histamine, but at relatively high concentrations Conclusions These data support the theory that the flare reaction to local histamine injection or release is a neurogenic reflex not involving histamine release at its effector end.     

Comparative efficacy of H1 antihistamines.

Second-generation H1 receptor antagonists (cetirizine, terfenadine, astemizole, loratadine, azelastine, and acrivastine) offer several important advantages over the older first-generation antihistamines. They are substantially less sedating and have little or no anticholinergic activity. Many of them are effective for 12 to 24 hours, thereby increasing compliance. In addition to acting as competitive inhibitors of histamine, several seem to have other antiallergic mechanisms as well. They are all absorbed well when taken orally. Many studies demonstrate their effectiveness compared with placebo in the treatment of seasonal and perennial rhinitis and chronic urticaria, and several studies suggest that they have a role in the treatment of bronchial asthma. A number of multicenter, double-blind, placebo-controlled studies comparing the effectiveness of terfenadine, 60 mg bid, with chlorpheniramine, 8 mg bid, in seasonal allergic rhinitis demonstrate that both drugs are approximately equally potent in reducing the symptoms of sneezing, rhinorrhea, and nasal itching and are statistically significantly better than placebo. Ocular symptoms were reduced somewhat less but still significantly. No differences from placebo were recorded in their effect on nasal congestion. The effectiveness of cetirizine, 10 mg once daily, compared with astemizole, 10 mg once daily, was measured in double-blind, placebo-controlled studies of patients with seasonal allergic rhinitis. These studies also demonstrate statistically significant benefit from the study drugs compared with placebo in relieving all nasal symptoms except congestion. Both drugs also relieved ocular pruritus. Fewer studies have assessed azelastine, acrivastine, and loratadine, but all have been shown to provide significant relief of seasonal allergic rhinitis compared with placebo.(ABSTRACT TRUNCATED AT 250 WORDS)     

A double‐blind, single‐dose, crossover comparison of cetirizine, ebastine, epinastine, fexofenadine, terfenadine, and loratadine versus placebo: suppression of histamine‐induced wheal and flare response for 24 h in healthy male subjects

BACKGROUND: New H1-antagonists have become available, but there has been no comparison of their potency for inhibiting histamine in the skin. METHODS: Cetirizine 10 mg, ebastine 10 mg, epinastine 20 mg, fexofenadine 60 mg, terfenadine 60 mg, loratadine 10 mg, or placebo was given to 14 healthy male volunteers in a double-blind, crossover randomized manner. Inhibition of the wheal and flare response to epicutaneous histamine phosphate (100 mg/ml) challenge was measured at 0, 0.5, 1, 2, 4, 6, 8, 10, 12, and 24 h after doses. RESULTS: Epinastine inhibited the wheal and flare after 30 min. Cetirizine commenced acting at 1 h and was superior to other treatments. Ebastine was no better than placebo until 4 h, but was efficacious thereafter until 24 h. Terfenadine induced potent inhibition after 1 h and was superior to its metabolite fexofenadine. Loratadine was the least potent inhibitor. Inhibition of the flare response paralleled the patterns seen for wheals. The rank order for area under the curve (0-24 h) was cetirizine, epinastine, terfenadine, ebastine, fexofenadine, loratadine, and placebo. CONCLUSIONS: The inhibition of histamine effects in the skin may be useful in predicting the clinical utility of newly introduced antihistamines in treating allergic disorders.     

Experimental models for the evaluation of treatment of allergic rhinitis.

OBJECTIVE: To review the experimental models used for the clinical evaluation of treatments for allergic rhinitis. DATA SOURCES: Peer-reviewed clinical studies and review articles were selected from the PubMed database using the following relevant keywords: allergic rhinitis in combination with efficacy, wheal and flare, nasal challenge, park, cat room, or exposure unit. Regulatory guidance documents on allergic rhinitis were also included. STUDY SELECTION: The authors' knowledge of the field was used to limit references with emphasis on recent randomized and controlled studies. References of historical significance were also included. RESULTS: Traditional outpatient studies are universally accepted in the evaluation of treatment for allergic rhinitis. Experimental models provide ancillary information on efficacy at different stages of treatment development. Skin histamine and allergen challenge, as well as direct nasal challenge with histamine and allergen, are often used as early steps in assessing drug efficacy. Exposure units, park settings, and cat rooms better approximate real life by drawing on the natural mode of allergen exposure and delivering the sensitizing allergen to allergic individuals in the ambient air. Park studies make use of allergens in the outdoors, whereas cat rooms and exposure units present the sensitizing allergens indoors, with the latter providing consistent predetermined allergen levels. Exposure unit and park studies are acknowledged for the determination of onset of action and are also suited to the measurement of duration of effect and other measures of efficacy. Onset and duration of effect are 2 important pharmacodynamic properties of antihistamines and nasal corticosteroids as determined by the Allergic Rhinitis and Its Impact on Asthma and the European Academy of Allergology and Clinical Immunology workshop group. CONCLUSIONS: All challenge models serve as important instruments in the evaluation of antiallergic medications and provide additional information to complement traditional studies.     

Efficacy of ebastine, cetirizine, and loratadine in histamine cutaneous challenges.

BACKGROUND: Few studies have compared the antihistaminic effect of ebastine at 20 mg/day (maximal recommended daily dose) with the effect found for other antihistamines in human pharmacologic models. OBJECTIVE: To compare the inhibition of the histamine-induced skin reaction produced by ebastine (20 mg/day) with that produced by cetirizine (10 mg/day), loratadine (10 mg/day), or placebo in a double-blind, randomized, crossover, placebo-controlled clinical trial. METHODS: Twenty volunteers (10 men and 10 women) received the four treatments once daily for 7 days, with a mean 7-day washout period between treatments. Three intradermal histamine challenges (0.05 mL of a 100 microg/mL histamine solution at 4, 8, and 24 hours after drug administration) were performed at baseline, day 1 (single dose), and day 7 (multiple doses). Wheal and flare areas were measured after 15 minutes. RESULTS: All treatments yielded significant reductions of histamine-induced wheal in comparison to placebo (P < 0.001). Analysis of covariance revealed significant differences between treatments (P < 0.05). Ebastine had a significantly greater antihistaminic effect than did cetirizine or loratadine, except at 4 hours after a single dose versus cetirizine. Further, the effect of cetirizine was similar with single or multiple doses after both 4 and 24 hours, whereas the effect of ebastine showed significant increases in wheal reduction with multiple doses (P < 0.05). No serious adverse events or withdrawals occurred during the study. CONCLUSION: This study shows that ebastine in a 20-mg dose is an effective once-daily antihistamine. Superior efficacy was found in comparison to cetirizine (10 mg) or loratadine (10 mg) on the overall skin wheal response after single and multiple doses.     

Rupatadine for the treatment of allergic rhinitis and urticaria

Allergies are a widespread group of diseases of civilization and most patients are still undertreated. Since histamine is considered to be the most important mediator in allergies such as allergic rhinitis and urticaria, the most commonly used drugs to treat these disorders are antihistamines acting on the histamine 1 (H1) receptor. The currently available antihistamines, however, have significant differences in their effects and safety profiles. Furthermore, the Allergic Rhinitis and its Impact on Asthma initiative calls for additional desirable properties of antihistamines. Here, we review the profile of rupatadine, a new dual platelet-activating factor and H1-receptor antagonist that fulfils these criteria and therefore offers an excellent option for the treatment of allergic diseases.     

An overview of the novel H1-antihistamine bilastine in allergic rhinitis and urticaria

Currently available second-generation H1-antihistamines include a wide group of drugs with a better therapeutic index (or risk-benefit ratio) than the classic antihistamines, although their properties and safety profiles may differ. Bilastine is a newly registered H1-antihistamine for the oral treatment of allergic rhinitis and urticaria, with established antihistaminic and antiallergic properties. Clinical studies in allergic rhinitis and chronic urticaria show that once-daily treatment with bilastine 20 mg is effective in managing symptoms and improving patient's quality of life, with at least comparable efficacy to other nonsedative H1-antihistamines. As far as studies in healthy volunteers, clinical assays and clinical experience can establish, bilastine's safety profile is satisfactory, since it lacks anticholinergic effects, does not impair psychomotor performance or actual driving, and appears to be entirely free from cardiovascular effects.     

Histamine skin test reactivity following single and multiple doses of azelastine nasal spray in patients with seasonal allergic rhinitis.

OBJECTIVE: To determine whether azelastine nasal spray suppresses the dermal response to epicutaneous histamine in allergic patients and the duration of suppression after azelastine use is discontinued. METHODS: Seventy-eight patients with seasonal allergic rhinitis were entered into this randomized, double-blind, parallel-group, placebo-controlled study. Patients received either azelastine nasal spray (2 sprays per nostril twice daily) or placebo nasal spray for 14 days. Skin tests were performed 5 hours after the first dose of study drugs to determine the effect of a single dose of azelastine nasal spray on the wheal-and-flare response to histamine. At the end of the 14-day treatment period, skin tests were performed 5 hours after the last dose of study drugs and at 24-hour intervals thereafter, until each patient's wheal-and-flare response to histamine (1.0 and 5.0 mg/mL) returned to within 20% of baseline values. RESULTS: A single dose of azelastine nasal spray did not significantly alter the wheal-and-flare response to histamine. The wheal response was within 20% of the baseline value in 82% and 88% (1.0 and 5.0 mg/mL of histamine, respectively) of the patients 5 hours after discontinuing 14 days of treatment with azelastine nasal spray. Wheal responses were within 20% of baseline values 48 hours after treatment was discontinued, whereas flare responses returned to within 20% of baseline within 48 hours in 92% of the patients. CONCLUSIONS: Azelastine nasal spray should be discontinued for at least 48 hours before beginning allergy skin test procedures.