H1- and H2-antagonists in allergic and pseudoallergic diseases

Combination of H1 and H2 Histamine Receptor Antagonists: Current Knowledge and Perspectives of a Classic Treatment Strategy

Histamine receptor antagonists, which can bind to specific histamine receptors on target cells, exhibit substantial therapeutic efficacy in managing a variety of histamine-mediated disorders. Notably, histamine H1 and H2 receptor antagonists have been extensively investigated and universally acknowledged as recommended treatment agents for numerous allergic diseases and acid-related disorders, respectively. Historically, the combination of H1 and H2 receptor antagonists has been considered a classic treatment strategy, demonstrating relatively superior efficacy compared with single-drug therapies in the treatment of diverse histamine-mediated diseases. The latest emerging studies have additionally suggested the underlying roles of histamine and H1R and H2R in the development of anxiety disorders, arthritic diseases, and postexercise hypotension. Nevertheless, there is still a lack of systematic reviews on the clinical efficacy of combination therapy, greatly limiting our understanding of its clinical application. Here, we present a comprehensive overview of the current knowledge and perspectives regarding the combination of H1 and H2 histamine receptor antagonists in various histamine-mediated disorders. Furthermore, we critically analyze the adverse effects and limitations associated with combination therapy while suggesting potential solutions. Our review can offer a systematic summary and promising insights into the in-depth and effective application of the combination of H1 and H2 receptor antagonists.

Pharmacogenomics for the efficacy and side effects of antihistamines

Antihistamines, especially H1 antihistamines, are widely used in the treatment of allergic diseases such as urticaria and allergic rhinitis, mainly for reversing elevated histamine and anti-allergic effects. Antihistamines are generally safe, but some patients experience adverse reactions, such as cardiotoxicity, central inhibition, and anticholinergic effects. There are also individual differences in antihistamine efficacy in clinical practice. The concept of individualized medicine has been deeply rooted in people's minds since it was put forward. Pharmacogenomics is the study of the role of inheritance in individual variations in drug response. In recent decades, pharmacogenomics has been developing rapidly, which provides new ideas for individualized medicine. Polymorphisms in the genes encoding metabolic enzymes, transporters, and target receptors have been shown to affect the efficacy of antihistamines. In addition, recent evidence suggests that gene polymorphisms influence urticaria susceptibility and antihistamine therapy. Here, we summarize current reports in this area, aiming to contribute to future research in antihistamines and clinical guidance for antihistamines use in individualized medicine.

Comparison of cellular mechanisms underlying histamine release from rat mast cells induced by ionic and nonionic radiographic contrast media

PURPOSE

To determine the cellular mechanisms underlying mast cell histamine release induced by ionic and nonionic radiographic contrast media.

MATERIALS AND METHODS

Histamine release from rat pulmonary mast cells was measured after incubation with various radiographic contrast media. The cellular cAMP content was determined by an enzymatic immunoassay.

RESULTS

Both ionic and nonionic contrast media stimulated the histamine release, although the former was more potent than the latter. Dibutyryl cAMP suppressed histamine release evoked by ionic but not nonionic contrast media in a manner dependent on A kinase. The cellular cAMP content was lowered only by ionic contrast media. However, a secretory phospholipase A2 inhibitor p-bromophenacyl bromide inhibited both ionic and nonionic contrast media-evoked histamine releases.

CONCLUSION

We demonstrated for the first time the difference and similarity in the cellular mechanisms underlying histamine release induced by ionic and nonionic contrast media, in which the reduction in cAMP was specific for ionic materials and the activation of secretory phospholipase A2 may be common to both agents.

Desloratadine in the treatment of chronic idiopathic urticaria

Chronic idiopathic urticaria (CIU) is a common dermatologic disorder that may severely impair quality of life. Patients may suffer symptoms such as pruritus and disfigurement due to wheals for years or decades. Advances have been made in the last 10 years with the identification of an autoimmune pathogenesis in a significant proportion of patients. Despite this, treatment remains symptomatic, and antihistamines are the first choice of therapy once the diagnosis of CIU has been established. The goal of treatment is rapid, long-lasting symptom relief, and currently available antihistamines fail to provide this in many cases. Desloratadine is a novel, potent H1-receptor antagonist with additional inhibitory effects on inflammatory mediators such as cytokines and adhesion molecules. Newly published data on the efficacy and safety of desloratadine in CIU is highly encouraging, suggesting that the drug may improve symptom control above that currently available.

Antihistamines in urticaria

Urticaria is one of the most common and, in its chronic course, excruciating dermato-allergic diseases. Apart from the dermatological diagnosis, the identification and evaluation of causal triggering factors is of utmost importance. Here a 'three-step guideline' (according to Ring and Przybilla) has gained acceptance, ranging a general basic examination via an intensive investigation until oral provocation tests for food allergy and oral provocation tests for idiosyncrasy (OPTI) against food additives. Apart from true IgE-mediated allergies, pseudo-allergic reactions against food additives as well as food contents represent a major problem in chronic urticaria. Recently gastric mucosal colonization with Helicobacter pylori as the trigger of chronic urticaria has received attention. New pathophysiological concepts describe autoantibodies that are directed either against IgE or against the high-affinity IgE-receptor on the surface of mast cells and basophil leucocytes. In the intradermal test with autologous serum positive wheal and flare reactions can be observed (Greaves' test). In many patients with chronic urticaria considerable psychosomatic involvement is also observed. Histamine is one of the major mediators of most forms of urticaria although in some cases, especially physical urticaria, other mediators seem to play a role. Therefore antihistamines, and mainly H1 antihistamines, are the mainstay of antiurticaria therapy. Some studies have shown a benefit of combined H1- and H2-antagonist treatment in special forms of urticaria namely urticaria factitia. Similarly pretreatment with combined H1 and H2 antagonists has been proven to reduce effectively the frequency of pseudo-allergic reaction to some histamine-releasing drugs used in radiology or surgery. More than 50 years after the first introduction of an antihistamine into allergy therapy, antihistamines still represent modern and exciting agents contributing to the continuous improvement of antiallergic therapy. Antihistamine therapy can be performed with either the classical or second generation antihistamines. Classical antihistamines are connected with considerable side-effects especially sedation and anticholinergic effects. New non-sedating antihistamines have been developed that do not cross the blood-brain barrier. The efficacy of mizolastine, a new non-sedating H1 antagonist, has been evaluated in several placebo-controlled and comparative clinical trials. Overall, mizolastine 10 mg/day was found to be significantly more effective than placebo and as effective as other second generation antihistamine drugs in the management of patients with chronic urticaria, with a rapid and sustained action.

The influence of the H1 and H2 receptor antagonists, terfenadine and ranitidine on the hypotensive and gastric pH effects of the histamine releasing drugs, morphine and tubocurarine

Morphine and tubocurarine may release histamine by direct mast cell degranulation which may result in systemic effects such as cutaneous flushing, local wheal and flare formation and hypotension. This randomised, double-blind study examined whether preoperative combined oral terfenadine (60 mg) and ranitidine (150 mg) attenuates the reduction in blood pressure and cutaneous flushing after the administration of tubocurarine and morphine in 60 patients undergoing elective gynaecological surgery. In addition, investigation was made of whether tubocurarine and morphine cause a significant decrease in gastric pH in comparison to the nonhistamine-releasing agents fentanyl and vecuronium. Patients were randomly assigned to one of three groups receiving either pre-operative terfenadine and ranitidine and intra-operative tubocurarine and morphine (group A); pre-operative placebo and intra-operative tubocurarine and morphine (group B); pre-operative placebo and intra-operative fentanyl and vecuronium (group C). Compared to group B, group A had less hypotension and tachycardia but no significant decrease in cutaneous flushing immediately following morphine and tubocurarine (p > 0.05). There were no significant differences in haemodynamic changes between the groups A and C. In those patients not pretreated with terfenadine and ranitidine (groups B and C), gastric pH decreased between 5 and 10 min following bolus administration of morphine and tubocurarine (group B), whereas patients receiving fentanyl and vecuronium (group C) had an increase in gastric pH. This suggests that histamine release following administration of morphine and tubocurarine is sufficient to increase gastric acidity.(ABSTRACT TRUNCATED AT 250 WORDS)

Reações de hipersensibilidade imediatas após uso intravenoso de soros antivenenos: valor prognóstico dos testes de sensibilidade intradérmicos

Foram admitidos no Hospital das Clínicas da FMRPUSP, durante os anos de 1983 a 1988, 494 pacientes vítimas de acidentes ofídicos e escorpiônicos que receberam soro antiveneno (SAV) e nos quais foi avaliada a freqüência e tipo das manifestações imediatas, bem como o valor prognóstico do teste de sensibilidade. Do total de pacientes vítimas de ofidismo, 82 (25,6%) apresentaram reações imediatas, das quais as mais comuns foram as cutâneas, isoladas (40%) ou associadas com sintomas respiratórios (19%), seguidas de manifestações gastrintestinais (17%). Choque anafilático foi detectado em 10 pacientes (12%). Em relação aos acidentes escorpiônicos, reações imediatas foram observadas em 13 pacientes (7,5%), também com predomínio de lesões cutâneas. Sintomatologia cardiocirculatória foi detectada em apenas 1 paciente. Devido ao baixo valor preditivo positivo (31,8%) e à baixa sensibilidade (54,6%), propomos que o teste de sensibilidade intradérmico seja abolido da rotina de atendimento de urgência aos pacientes vítimas de acidentes por animais peçonhentos. Anti-histamínicos (bloqueadores dos receptores H1 e H2) e corticosteróides devem ser administrados por via parenteral anteriormente à soroterapia, no sentido de prevenir ou minimizar as reações de hipersensibilidade imediatas que podem ocorrer. O soro antiveneno deve ser sempre administrado por via intravenosa, de preferência sem diluição, gota a gota, durante 15 a 30 minutos, sob contínua supervisão da equipe médica.