Assessment of antihistamine efficacy and potency

Current recommendations and emerging options for the treatment of allergic rhinitis

Allergic rhinitis (AR) is one of the most common diseases and represents a global health problem, currently affecting up to 30% of the general population, with a continuously increasing prevalence and significant comorbidities and complications. The aim of this review is to provide an update on AR treatment, with a focus on current therapies defined by AR and its impact on asthma guidelines and with a particular emphasis on new and future therapeutic perspectives.

The effects of antihistamines with varying anticholinergic properties on voluntary and involuntary movement

OBJECTIVE

Recent evidence indicates that antihistamines can affect movement, which is most likely due to altered neurotransmission in cholinergic and histaminergic pathways. The purpose of this study was to determine if antihistamines with varying anticholinergic properties differentially affect voluntary and involuntary movement control.

METHODS

Eleven healthy subjects were enlisted into a human double blind, placebo-controlled, five-way crossover study. Drowsiness, reaction time, and physiological tremor were examined 1-, 2-, and 3-hr post-ingestion of antihistamines with known anticholinergic profiles. These were the first-generation promethazine, and second-generation loratadine, desloratadine, and fexofenadine. Hyoscine butylbromide was used in an additional experiment to determine how a peripheral antimuscarinic drug influenced neuromotor function.

RESULTS

Promethazine, desloratadine and fexofenadine increased drowsiness. Promethazine increased simple and choice reaction time and reduced tremor. Desloratadine increased choice reaction time and tremor, while loratadine slowed simple and choice reaction time.

CONCLUSION

Central anticholinergic and antihistaminergic properties of antihistamines potentially contribute to movement dysfunction.

SIGNIFICANCE

Second-generation antihistamines have provided the consumer with a safer alternative to the first-generation sedating antihistamine. However, the results of this study suggest that loratadine and desloratadine have the potential to affect movement control, and further research is warranted to understand the clinical relevance of these findings.

Atopy: pediatric ENT manifestations in children

OBJECTIVE

The aim of the present study is to discuss the basics of atopy in children in relationship to the principal ENT allergic disorders such as allergic rhinitis, rhinosinusitis and their impact on lower airways, allergic otitis media, and oral cavity focusing on their natural history.

METHODS

An updated and exhaustive review of principal literature on these topics is performed, underlining the constant but growing interest evoked by these disorders most of all the possible sequelae or complications. Considering the different districts which can be selectively or simultaneously affected by the allergic sensitisation, diagnosis can be a really hard task; in this paper, we tried to draw an integrated diagnostic approach to atopic children and some guidelines for a correct therapeutic approach.

CONCLUSIONS

Atopic disorders could expose young patients to years of chronic diseases that interferes with their development and with many important aspects of their lives. For these reasons, and considering the high social and medical costs of this disease, it is extremely important to adequately treat allergic pathologies from the early phases of its natural history. Moreover, we cannot forget that an appropriate therapy of allergic pathologies should not be only able to decrease symptoms but, it should also be able to improve patients health related quality of life.

Ebastine in the light of CONGA recommendations for the development of third-generation antihistamines

In 2003 a consensus group on new-generation antihistamines (CONGA) defined the characteristics required for a third-generation H(1) antihistamine as there had been much controversy about this issue since the early 1990s. One of the antihistamines that had been claimed to belong to such a group is the second-generation antihistamine, ebastine. The objective of this review is to analyze the pharmacology of ebastine, in light of the CONGA recommendations for the development of new-generation antihistamines: (1) anti-inflammatory properties, (2) potency, efficacy and effectiveness, (3) lack of cardiotoxicity, (4) lack of drug interactions, (5) lack of CNS effects, and (6) pharmacological approach. Ebastine seems to have anti-inflammatory properties that help to ameliorate nasal congestion, though this has not yet been conclusively demonstrated. Its pharmacological-therapeutic profile does not differ greatly from that of other second-generation antihistamines. Its cardiac safety has been widely assessed and no cardiac toxicity has been found at therapeutic doses despite initial concerns. The risk of potentially relevant drug interactions has been investigated and ruled out. Ebastine does not produce sedation at therapeutic doses and drug interaction studies with classical CNS depressants have not demonstrated a synergistic effect. Pharmacologically, ebastine is an H(1) inverse agonist. Perhaps the answer to the quest for new-generation antihistamines lies not only in H(1) but in a combined approach with other histamine receptors.

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.

Efficacy and central nervous system impairment of newer-generation prescription antihistamines in seasonal allergic rhinitis

Allergic rhinitis is a highly prevalent disorder and oral antihistamines are often used to manage patient symptoms. Older-generation antihistamines, such as diphenhydramine and chlorpheniramine, are effective at relieving the symptoms of seasonal allergic rhinitis (SAR); however, they are associated with adverse events, including sedation and impairment, at, or above, the recommended dose. Newer-generation antihistamines, such as desloratadine, cetirizine and fexofenadine, were developed to minimize adverse events. In this article, studies examining newer-generation antihistamines in adults and children were reviewed. The clinical evidence confirms that desloratadine, cetirizine and fexofenadine are effective at managing the symptoms of SAR in adults and children; however, cetirizine is more likely to cause sedation. Physician intervention is paramount to SAR symptom management. It is essential that appropriate treatment relieves SAR symptoms with absent or minimal adverse events. This is particularly important for those patients involved in skilled and cognitive activities or safety-critical jobs.

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.

Evaluation of the optimal oral antihistamine for patients with allergic rhinitis

Because of its bothersome symptoms, allergic rhinitis (AR) is 1 of the top 10 reasons for patient visits to primary care physicians. This highly prevalent disease also results in loss of productivity, both at work and in school. Oral antihistamines are one of the most frequently prescribed medications for the management of AR and, with several agents available, it is important to discern the specific benefits and detriments of each. To assess the differences in efficacy and safety factors among antihistamines, the Individual therapeutic window of each agent can be used as a comparative reference tool because it defines the dose range over which an antihistamine is efficacious and free of adverse effects. As such, the therapeutic window includes both undesired effects, such as sedation, and desired properties, such as rapid onset of action, long duration of efficacy, broad age range of applicability, and potential to Improve quality of life. Therefore, agents with broad therapeutic windows, based on both efficacy and safety, are expected to be more favorable; this therapeutic window should be understood by the primary care physician when prescribing a medication.

Management of Seasonal Allergic Rhinitis: Comparative Efficacy of the Newer-Generation Prescription Antihistamines

PURPOSE

To discuss the efficacy and safety of second-generation prescription antihistamines, cetirizine, desloratadine, and fexofenadine, and to inform nurse practitioners (NP) who are in a position to optimally manage patients presenting with seasonal allergic rhinitis (SAR).

DATA SOURCES

Selected published clinical trials.

CONCLUSIONS

NP, who are ideally placed to successfully manage the majority of patients with SAR, should be fully aware of the treatment options available. Although first-generation over-the-counter antihistamines are convenient to use and are readily accessible, patients run the risk of experiencing adverse effects, such as sedation. For this reason, second-generation antihistamines should be considered a better alternative; however, they need to be evaluated individually on the basis of their proven efficacy and safety. Both cetirizine and fexofenadine are equally effective at relieving the symptoms of SAR; however, cetirizine has been shown to be more likely to cause sedation and impairment.

IMPLICATIONS FOR PRACTICE

If left untreated, SAR can have a substantial effect on patients' quality of life, resulting in fatigue, irritability, sleep disorders, and cognitive impairment.

Desloratadine partially inhibits the augmented bacterial responses in the sinuses of allergic and infected mice

BACKGROUND

Allergic rhinitis (AR) is considered a major predisposing factor for the development of acute bacterial rhinosinusitis. How AR augments a bacterial infection is unknown.

OBJECTIVE

Our purpose in this study was to test whether an H1 receptor antagonist, desloratadine, could reduce the augmented effect of an ongoing allergic reaction on acute bacterial rhinosinusitis.

METHODS

Three groups of infected and ovalbumin (OVA)-sensitized mice were studied: (1) infected and allergic mice treated with desloratadine, (2) infected and allergic mice treated with placebo, and (3) infected mice. A fourth group of uninfected, non-sensitized mice served as a control for the cellular changes. BALB/c mice were sensitized by two intraperitoneal injections of OVA given 8 days apart. One day after the second injection, the mice were nasally exposed daily to 6% OVA (the groups treated with desloratadine or placebo) or phosphate-buffered saline (PBS) (the infection-only group) for 5 days. After the second OVA exposure, the mice were intranasally inoculated with Streptococcus pneumoniae. Desloratadine or placebo was given daily throughout the OVA exposure period. Nasal allergic symptoms were observed by counting of nasal rubbing and sneezing for 10 min after OVA or PBS nasal challenge. On day 5 post-infection, nasal lavage culture was done, and the inflammatory cells in the sinuses were evaluated by flow cytometry.

RESULTS

Mice that were made allergic, infected, and treated with placebo showed more organisms and phagocytes than did only infect mice. They also manifested allergic nasal symptoms and eosinophil influx into the sinuses. Desloratadine treatment during allergen exposure reduced allergic symptoms and reduced sinonasal infection (P<0.05). There tended to be less myeloid cell and neutrophil influx (P=0.09 both), but not eosinophil influx (P=0.85) compared with that in the placebo-treated group.

CONCLUSION

Desloratadine treatment during nasal challenge inhibited allergic symptoms and reduced sinonasal infection, suggesting that histamine via an H1 receptor plays a role in the augmented infection in mice with an ongoing allergic reaction.

Evaluation of the efficacy of antihistamines using human monocyte-derived dendritic cells stimulated with histamine

BACKGROUND

It has been reported that histamine induces CD86 expression and chemokine production in human immature monocyte-derived dendritic cells (MoDCs), which can be blocked by both H(1)- and H(2)-receptor antagonists.

OBJECTIVE

We sought to examine whether the efficacy of H(1)-type antihistamines can be assessed by using MoDCs.

METHODS

We examined the suppressive effects of 1 H(2)-type antihistamine (cimetidine) and 5 different H(1)-type antihistamines (cetirizine, diphenhydramine, ketotifen, olopatadine, and emedastine) on the induction of CD86 and IL-8 production by MoDCs from 23 healthy individuals stimulated with histamine. We also examined the responses of MoDCs from 13 patients with chronic urticaria to these antihistamines, and compared the in vitro efficacy with the actual clinical response to antihistamines evaluated by patient and physician assessments.

RESULTS

All the antihistamines we examined suppressed the increase of CD86(+) cells after histamine stimulation in a dose-dependent fashion, and all H(1)-type antihistamines were more efficacious than cimetidine. IL-8 production stimulated with histamine was also suppressed by cetirizine, ketotifen, and olopatadine. Unexpectedly, the suppressive effect of these antihistamines on the CD86 augmentation was highly variable among different healthy control participants. Interestingly, in 10 of 13 cases of chronic urticaria, this in vitro analysis of antihistamines correlated with the clinical response to antihistamines.

CONCLUSION

This study suggests that the evaluation of antihistamines using MoDCs can be a useful method for the screening of effective antihistamines, for the comparison of the efficacy of antihistamines, and for predicting the efficacy of antihistamines on an individual basis.

Role of antihistamines in ocular allergy

Although H(1) antihistamines are commonly used to treat allergic disorders and have demonstrated efficacy in allergic rhinoconjunctivitis, data on the effects of these agents specifically on ocular symptoms are limited. Oral H(1) antihistamines inhibit some symptoms of pruritus and erythema in laboratory models and have been shown to be superior to placebo for relief of symptoms in clinical trials. Eye drops typically provide faster relief of ocular symptoms than oral agents, and combination therapy with a topical agent and an oral agent has been found to be superior to the oral agent alone. In general, oral H(1) antihistamines have been considered superior to intranasal corticosteroids for relief of ocular symptoms, but some studies have shown equal efficacy for these agents, or even superior efficacy for intranasal corticosteroids.

Does potency predict clinical efficacy? Illustration through an antihistamine model

OBJECTIVE

The concepts of potency and efficacy are often confused and used interchangeably within the scientific and pharmaceutical industry. It is important that the distinction between the two is understood, and that the terms are defined within their correct context. After reading this article, readers should have an understanding of the relationships between receptor potency and clinical efficacy.

DATA SOURCES

Following a comprehensive review of the literature using MEDLINE, the author observed a lack of relevant references that relate measurements of potency to clinical efficacy. Therefore, the author reviewed the basic pharmacologic principles of potency using examples from the recent antihistamine literature.

RESULTS

Potency is an expression of the activity of a drug in terms of the concentration or amount of the drug required to produce a defined effect, whereas clinical efficacy judges the therapeutic effectiveness of the drug in humans. The differing methods of evaluating the activity of antihistamines in vitro and in vivo can lead to inconsistent results, which complicate the use of potency to predict clinical efficacy. Further, as therapeutic behavior is modulated by pharmacokinetic and pharmacodynamic parameters and by further interactions at sites other than the target receptor, it does not necessarily follow that more potent drugs have greater clinical efficacy.

CONCLUSIONS

Although potency can be a good preclinical marker of the therapeutic potential of a drug, clinical efficacy should only be evaluated within the patient population using appropriate outcome measures.

Effect of cetirizine, levocetirizine, and dextrocetirizine on histamine-induced nasal response in healthy adult volunteers

BACKGROUND

Cetirizine, an effective H1-receptor antagonist, is a racemate mixture of two enantiomers: levocetirizine (R enantiomer) and dextrocetirizine (S enantiomer).

METHODS

To investigate the pharmacologic activity of the two enantiomers of cetirizine, we conducted a randomized, double-blind, four-way, crossover study to assess the effect of treatment with 5 mg levocetirizine, 5 mg dextrocetirizine, and 10 mg cetirizine and matched placebo, on histamine-induced changes in the nasal airways of 24 healthy volunteers. Four hours after a single oral intake, all subjects were challenged by nasal aerosol application with increasing doubling concentrations (from 0.25 to 32 mg/ml) of histamine in both nostrils. Nasal resistance was measured by passive anterior rhinomanometry (PAR), and changes in histamine threshold were calculated together with the absolute number of sneezes after each challenge.

RESULTS

Both levocetirizine and cetirizine significantly attenuated the histamine-induced increase in nasal airway resistance by nearly 50% (from a median resistance of 2.51 Pa per cm3/s to 1.29 and 1.31 Pa per cm3/s, respectively) at the maximal concentration, and they concomitantly increased the histamine threshold by fourfold (from 8 to 32 mg/ml), compared with placebo. Sneezing was also attenuated by both levocetirizine and cetirizine. However, these antihistaminic effects were not seen with dextrocetirizine.

CONCLUSIONS

This study shows a similar activity of levocetirizine and cetirizine on the inhibition of histamine-induced increase in nasal resistance, indicating that the antihistaminic properties of cetirizine are probably attributable to levocetirizine.

A comparison of the anti-inflammatory properties of intranasal corticosteroids and antihistamines in allergic rhinitis

Allergic rhinitis manifests itself clinically due to the local release of mediators from activated cells within the nasal mucosa. Treatment strategies aim either to reduce the effects of these mediators on the sensory neural and vascular end organs, or to reduce the tissue accumulation of the activated cells that generate them. Corticosteroids intervene at a number of steps in the inflammatory pathway, and, by reducing the release of cytokines and chemokines, inhibit cell recruitment and activation. These effects are evident both in vivo and in vitro. While antihistamines also have some anti-inflammatory effects in vitro, these require higher concentrations than with corticosteroids and are not consistently reproduced in vivo. In addition, although antihistamines and corticosteroids might appear to have complementary mechanisms of action, clinical trials suggest that their co-administration does not confer any additional long-term benefits compared with that achieved with corticosteroids alone. Topical corticosteroids are therefore the preferred anti-inflammatory therapy for persistent allergic rhinitis.

Allergic rhinitis: treating the adult

Allergic rhinitis is now recognized as a chronic medical condition that markedly affects patient quality of life and is a cause of substantial medical care expenditures. Effective treatment of adults with allergic rhinitis usually requires an integrated regimen that combines allergen avoidance measures, pharmacotherapy, and possible specific-allergen immunotherapy. This approach can control bothersome symptoms with minimal adverse effects in most patients. New medications, such as anti-immunoglobulin E therapy and cytokine antagonists, may provide relief to patients who are refractory to or do not tolerate currently available treatments.