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PubMedDate not supplied

Antihistamines in the treatment of dermatitis.

BACKGROUND: Atopic dermatitis (AD) is an inflammatory skin disorder that is exceedingly challenging to treat. A prominent feature of AD is chronic pruritus. Early evidence suggested that pruritus in AD was partially due to mast cell release of histamines. Conversely, recent studies do not validate the role of histamine in the pathogenesis of pruritus. Conventional management continues to include the wide use of antihistamines to treat the persistent itch, however, there is an urgent need for therapy which will reduce the severity of pruritus for these patients. OBJECTIVE: To review the evidence in the literature for the use of antihistamines in the treatment of atopic dermatitis. METHODS: A MEDLINE search (1966-2002) was performed to obtain studies examining the use of antihistamines in the treatment of atopic dermatitis. Search terms included: atopic dermatitis; eczema; antihistamines; azatadine; brompheniramine; cetirizine; chlorpheniramine; clemastine; cyclizine; cyproheptadine; desloratadine; diphenhydramine; fexofenadine; hydroxyzine; loratadine; meclizine; promethazine; trimeprazine. Further references were gathered from these publications. RESULTS: Historically, antihistamines have been used in the treatment of AD. However, this review shows that the evidence for its use is inconclusive. At present, several antihistamines continue to provide relief of pruritus by central sedation, and they can also be used therapeutically for concomitant allergic conditions associated with AD. More clinical trials examining the therapeutic efficacy of antihistamines, especially with the newer nonsedating antihistamines, are necessary to elucidate their role in the treatment of AD. CONCLUSION: Dermatologists require additional evidence regarding the efficacy of antihistamines and their mechanism of action in the treatment of AD to enhance patient care.

Dermatitis, Atopic↗
PubMed2006

Assessment of the first and second generation antihistamines brain penetration and role of P-glycoprotein.

PURPOSE: The sedating effect of first generation H(1)-antihistamines has been associated with their ability to penetrate the blood-brain barrier (BBB) and lack of efflux by P-glycoprotein (Pgp). Second generation H(1)-antihistamines are relatively free of sedation and their limited brain penetration has been suggested to arise from Pgp-mediated efflux. The objective of this work was to evaluate the role of Pgp in brain penetration of first and second generation antihistamines. METHODS: Potential of antihistamines to be Pgp substrates was tested in vitro using Madin Darby canine kidney cells transfected with human Pgp. The role of Pgp in limiting brain penetration of antihistamines was tested by using the in situ brain perfusion technique. RESULTS: Majority of antihistamines were Pgp substrates in vitro. Following in situ brain perfusion, the first generation antihistamines substantially penetrated into rat brain independently from Pgp function. The second generation antihistamines terfenadine and loratadine, achieved substantial brain penetration, which was further enhanced by Pgp inhibition by cyclosporin A (CSA). In contrast, fexofenadine and cetirizine, penetrated brain poorly regardless of CSA administration. CONCLUSIONS: Antihistamines greatly differ in their ability to cross the BBB as well as in the role of Pgp in limiting their transport into the CNS in vivo.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1994

Incidence and clinical importance of perioperative histamine release: randomised study of volume loading and antihistamines after induction of anaesthesia. Trial Group Mainz/Marburg.

Although histamine release is recognised as a common event during anaesthesia and surgery, few clinicians judge the resultant cardiorespiratory disturbances serious enough to warrant prophylaxis with antihistamines. We have assessed the incidence and importance of histamine release in a randomised 2 x 2 factorial study. 240 patients representing a routine throughput of major general surgery were studied during a standardised induction of anaesthesia and preoperative loading of the circulation with either Ringer solution or Haemaccel-35, with or without antihistamine prophylaxis with dimetindene (H1) plus cimetidine (H2). Cardiorespiratory disturbances were graded as detectable, clinically relevant, or life-threatening from observers' records of the anaesthesia and the actions taken by the anaesthetists. Disturbances that were accompanied by significant rises in plasma histamine were further designated histamine-related, and those that were not were designated histamine-unrelated. Anaesthetists, observers, and designators were blinded to whether or not the patients had received antihistamines and to which solution was used for circulatory volume loading. Clinically relevant or life-threatening histamine-related disturbances occurred in 8% of the patients who after induction of anaesthesia received Ringer without antihistamines, in 26% of those who received Haemaccel without antihistamines, and in 2% or less of those who received antihistamines (p < or = 0.0001). There were 4 life-threatening histamine-related disturbances, all in patients who received Haemaccel without antihistamines (p < 0.01). Histamine-unrelated disturbances occurred in 16% overall, with no obvious effect of Haemaccel or antihistamines. The histamine-related disturbances under anaesthesia were remarkable for their severity (even with small rises in histamine concentrations), for the prevalence of bradycardia, and for the absence of skin signs. Their likelihood and severity were increased in patients with tumours. The results of the trial make a case for routine prophylaxis with antihistamines as part of anaesthetic management.

Adolescent↗
PubMed1999

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.

Benzimidazoles↗
PubMedDate not supplied

Identification of allergic disease among users of antihistamines.

OBJECTIVE: Patients exhibit a multitude of symptoms that may or may not be allergy related. In this study, we examined the consistency between results obtained by a multiallergen-specific immunoglobulin E (IgE) test and frequent use (3 months or more) of prescribed antihistamines. METHODS: A retrospective examination of 1-year prescription claims records from January 1, 2000, through December 31, 2000, for 4,643 patients enrolled in a 115,000-member managed care organization who received 1 or more prescriptions for an oral antihistamine (loratadine, fexofenadine, or cetirizine). RESULTS: A total of 1,343 health plan enrollees who received an oral antihistamine prescription were continuously enrolled during the year 2000 and diagnosed with allergic rhinitis. Of these patients, 246 (18%) consented to a multiallergen- specific IgE test, and 159 patients (64.6%) had a negative IgE test result. A total of 163 patients were classified as frequent antihistamine users (3 or more antihistamine prescriptions), and 101 (62.0%) of these patients had negative test results. Our study demonstrated no relation between prescribed antihistamine use and patient sensitization status. CONCLUSIONS: Only 35.4% of the patients who used an oral antihistamine and were diagnosed with an allergy tested positive to the multiallergen-specific IgE test, and only 38% of the patients with records of frequent antihistamine use and who were diagnosed as allergic tested positive to the multiallergen-specific IgE test. Apparently, there are patients taking medications prescribed for allergic rhinitis who are, in fact, not allergic, which is both wasteful economically and not indicated medically. Additional evaluation may be advisable to support the clinical diagnosis of allergy for patients presenting with allergy-like symptoms who use antihistamines frequently.

Adult↗
PubMed1999

Comparative tolerability of second generation antihistamines.

Second generation histamine H1 receptor antagonists, the so-called 'nonsedating' antihistamines, have high potency and additional antiallergic properties as well as H1 antagonism and are associated with fewer adverse effects compared with the first generation antihistamines. A number of drugs in this class are approved for use: acrivastine, astemizole, azelastine, cetirizine, ebastine, fexofenadine, loratadine, mizolastine and terfenadine. All of them have a more favourable risk-benefit ratio with regard to the CNS adverse effects. Even those second generation antihistamines that are not actually 'nonsedating' are less impairing than their predecessors, but not one of them is entirely devoid of CNS activity. Under certain circumstances some antihistamines may affect cardiac repolarisation resulting in cardiovascular adverse effects. Serious cardiovascular effects have been reported with terfenadine and astemizole when they are used in high dosages or when they are given to 'at risk' patients. Animal models indicate that there might be a potential risk of cardiovascular adverse effects with other antihistamines as well. However, up to now there is no clinical evidence for this assumption, despite some confusing reports. Likewise there has been much discussion about a link between these agents and carcinogenicity. However, there is no evidence that any of the second generation antihistamines increase the risk of tumour growth in humans. Small children, elderly patients and persons with chronic renal or liver impairment are special groups in which the individual adverse effects of the second generation antihistamines must be kept in mind. The dosage for an individual has to be modified with respect to their metabolic situation. Despite the fact that some of the second generation antihistamines are listed in the US Food and Drug Administration pregnancy risk classification as class B, the use of second generation antihistamines should be avoided during pregnancy and they should never be administered to nursing mothers. Taking into account their negligible CNS activity, the low incidence of cardiovascular adverse effects, their lack of anticholinergic effects and other benefits, this class of antiallergic drugs represents a definite advance in therapy.

Age Factors↗
PubMed2006

New antihistamines: a critical view.

OBJECTIVES: To perform a critical evaluation of the more recent H1 antihistamines and the various terms used to describe them, based on a review of evidence on their role in the treatment of allergic disorders. SOURCES OF DATA: Original articles, reviews and consensus documents published from 1998 to 2006 and indexed in the MEDLINE and PubMed databases. Keyword: antihistamines. SUMMARY OF THE FINDINGS: Second-generation antihistamines differ from first-generation ones because of their elevated specificity and affinity for peripheral H1 receptors and because of their lower penetration of the central nervous system (CNS), having fewer sedative effects as a result. Whilst second-generation antihistamines are in general better tolerated than their predecessors, some adverse effects, principally cardiotoxicity, have been observed with some of them. Over the last 20 years, new compounds with different pharmacokinetic properties have been synthesized. The majority of these exhibit anti-inflammatory properties that are independent of their action on the H1 receptor. More recent improvements, generally in the form of active metabolites, led to the use of the term third-generation antihistamines. This term emerged spontaneously, with no clear definition of its meaning or clinical implications, creating great confusion among healthcare professionals. CONCLUSION: On the basis of the evidence on H1 antihistamines, none of them deserve the title "third-generation antihistamine." As the Consensus Group on New Generation Antihistamines concluded, to merit this definition, a new class of antihistamines would have to demonstrate distinct clinical advantages over existing compounds and fulfill at least three prerequisites: they should be free from cardiotoxicity, drug interactions and effects on the CNS.

Anti-Allergic Agents↗
PubMed1999

The current cardiac safety situation with antihistamines.

Antihistamines (H1-receptor antagonists) are amongst the most frequently prescribed drugs worldwide for the treatment of allergic conditions. The clinical interest of classical 'first generation' antihistamines is currently rather limited by their anticholinergic and sedative properties. The second generation of antihistamines, so-called non-sedating antihistamines, are free of these side-effects. However, since the 1990s, there have been reports that certain non-sedating antihistamines, mainly terfenadine and astemizole, might be associated with the risk of rare but severe dysrhythmias. These drugs prolong the monophasic action potential and surface electrocardiographic QT interval and may lead to the development of early after-depolarization and possibly torsades de pointes through an inhibition of potassium channel repolarization. Concomitant administration with drugs that inhibit the hepatic cytochrome P-450 (imidazole antifungals, macrolide antibiotics) or those that prolong the QT interval by the same or other mechanism (e.g. antiarrhythmics, antipsychotics, tricyclic antidepressants) increases their effect on the cardiac repolarization. The cardiac safety profile of newer non-sedating antihistamines requires confirmation. Drugs with low or no potential to block the K + rectification channel (e.g. IKr channels) are likely to possess cardiac safety advantages. Other drug-related factors such as the physico-chemical properties of the antihistamines and its metabolic profile may also contribute to the cardiac response. Mizolastine is a new non-sedating antihistamine with antiallergic properties. It has a good bioavailability and a metabolism via the cytochrome P-450 oxidation accounting for only 35% of its hepatic clearance. In addition, mizolastine displays low lipophilicity and consequently low cardiac tissue fixation. In clinical studies, mizolastine has not shown any dose-related increase in QT intervals. Its clinical use has not been associated with ventricular dysrhythmias. Thus, although the post-marketing experience with mizolastine is still limited, mizolastine offers a safe alternative for the therapeutic management of allergic rhinitis and urticaria. However, more data are still needed on the cardiac safety of this and other non-sedating antihistamines.

Benzimidazoles↗
PubMed2002

Antihistamines in urticaria and angioedema.

H1-antihistamines are the cornerstone of symptomatic treatment in acute and chronic urticaria, in which they not only relieve itching, but also reduce the number, size, and duration of urticarial lesions. Relief of whealing, flaring, and erythema may be incomplete as the vascular effects of histamine are mediated to its action at H2-receptors as well as at H1-receptors, and other vasoactive substances may also be involved. In randomized, prospective, placebo-controlled, double-blind studies, the new low-sedating H1-antihistamines have been found to be effective and safe in urticaria. Sedating antihistamines, although effective, place patients at risk for adverse effects, including decreased psychomotor performance. The response to H1-antihistamines in some types of urticaria, for example, in urticarial vasculitis, is unsatisfactory. An H2-antihistamine administered concurrently with an H1-antihistamine may modestly enhance relief of itching and wheal formation in some patients with urticaria refractory to treatment with an H1-antihistamine alone. The available evidence does not justify the routine addition of H2-antihistamine treatment to H1-antihistamine treatment.

Angioedema↗
PubMed1999

An evidence-based review of the efficacy of antihistamines in relieving pruritus in atopic dermatitis.

OBJECTIVE: To critically review the body of clinical trials that refute or support the efficacy of antihistamines in relieving pruritus in patients with atopic dermatitis. DESIGN: Review of MEDLINE from 1966 through March 1999, the Cochrane Database of Systematic Reviews, and Best Evidence to identify therapeutic trials of antihistamines in patients with atopic dermatitis. MAIN OUTCOME MEASURES: All randomized controlled trials or clinical trials of antihistamines used in the treatment of atopic dermatitis. We found 16 studies throughout the literature. RESULTS: Large, randomized, double-blind, placebo-controlled clinical trials with definitive conclusions (grade A trials) have not been performed. Two grade B trials (small, rigorous, randomized trials with uncertain results due to moderate to high alpha or beta error) refuted the use of antihistamines in relieving pruritus. One grade B trial supported the efficacy of antihistamines in relieving pruritus. All remaining trials (grade C) lacked placebo controls or randomization, or contained fewer than 20 patients in each treatment group. CONCLUSIONS: Although antihistamines are often used in the treatment of atopic dermatitis, little objective evidence exists to demonstrate relief of pruritus. The majority of trials are flawed in terms of the sample size or study design. Based on the literature alone, the efficacy of antihistamines remains to be adequately investigated. Anecdotally, sedating antihistamines have sometimes been useful by virtue of their soporific effect and bedtime use may be warranted. There is no evidence to support the effectiveness of expensive nonsedating agents.

Clinical Trials as Topic↗
PubMed1994

Optically active analogues of ebastine: synthesis and effect of chirality on their antihistaminic and antimuscarinic activity.

A series of optically active analogues of the H1-antihistamine ebastine, with chiral center(s) at the benzhydryl and/or phenylbutyl part of the molecule, have been synthesized. Their in vitro antihistaminic and antimuscarinic activities were investigated, along with a molecular modelling study. It was found that introduction of the benzhydryl chiral center yielded significant stereoselectivity for both antihistaminic and antimuscarinic activities. The steric preferences of the benzhydryl chiral center for antihistaminic and antimuscarinic actions were mirror images of each other. The (-)-isomer of 4-methylebastine (6d) showed more than 10-fold higher in vitro antihistaminic potency than ebastine. Meanwhile the selectivity of 6d for histamine H1-receptors was also increased by more than 20 times in comparison with ebastine. The chirality at the phenylbutyl part of the molecule does not significantly alter the antihistaminic or antimuscarinic activity of the compounds although the (S)-isomers showed slightly but unanimously higher antihistaminic activity than the (R)-isomers. These results have been discussed with existing stereoselectivity data of antihistamines and an asymmetric pharmacophore model for H1-antagonists has been described.

Animals↗
PubMed2003

H1-Antihistamines: more relevant than ever in the treatment of allergic disorders.

Histamine is an important chemical mediator of inflammation, vasodilation, increased vascular permeability, decreased peripheral resistance, airway smooth muscle contraction, and sensory nerve stimulation causing itching. It also plays a significant role in neurotransmission and in cardiac function. In allergic rhinoconjunctivitis and urticaria, there is strong evidence for the role of H(1)-antihistamine treatment. In asthma, additional dose-response studies, including higher doses of antihistamines than those used in allergic rhinitis, are needed to determine the role of antihistamines. In atopic dermatitis, the itch-relieving topical glucocorticoid-sparing effects of H(1)-antihistamines also require further documentation. The potential benefits of each H(1)-antihistamine should be weighed against the potential risks, and second-generation H(1)-antihistamines with excellent, well-documented safety records should be used in preference to older, less safe H(1)-antihistamines. Second-generation H(1)-antihistamines are more relevant than ever in the treatment of allergic disorders.

Dose-Response Relationship, Drug↗
PubMed2005

Second-generation antihistamines: actions and efficacy in the management of allergic disorders.

Antihistamines are useful medications for the treatment of a variety of allergic disorders. Second-generation antihistamines avidly and selectively bind to peripheral histamine H1 receptors and, consequently, provide gratifying relief of histamine-mediated symptoms in a majority of atopic patients. This tight receptor specificity additionally leads to few effects on other neuronal or hormonal systems, with the result that adverse effects associated with these medications, with the exception of noticeable sedation in about 10% of cetirizine-treated patients, resemble those of placebo overall. Similarly, serious adverse drug reactions and interactions are uncommon with these medicines. Therapeutic interchange to one of the available second-generation antihistamines is a reasonable approach to limiting an institutional formulary, and adoption of such a policy has proven capable of creating substantial cost savings. Differences in overall efficacy and safety between available second-generation antihistamines, when administered in equivalent dosages, are not large. However, among the antihistamines presently available, fexofenadine may offer the best overall balance of effectiveness and safety, and this agent is an appropriate selection for initial or switch therapy for most patients with mild or moderate allergic symptoms. Cetirizine is the most potent antihistamine available and has been subjected to more clinical study than any other. This agent is appropriate for patients proven unresponsive to other antihistamines and for those with the most severe symptoms who might benefit from antihistamine treatment of the highest potency that can be dose-titrated up to maximal intensity.

Adolescent↗
PubMed2002

Potential cardiac toxicity of H1-antihistamines.

Nonsedating H1-antihistamines are widely prescribed for the treatment of allergic disorders because of their lack of sedative and anticholinergic effects; however, certain nonsedating antihistamines such as terfenadine and astemizole are now known to cause QT prolongation and TdP, particularly in overdosage or with concomitant ingestion of imidazole antifungals or macrolide antibiotics. Mechanistic studies showed that the cardiotoxic effects of some nonsedating antihistamines are due to the inhibition of repolarization potassium channels, particularly IKr, which leads to prolongation of the action potential and QT interval, and the development of early after-depolarization, which triggers TdP. Patients at risk of developing TdP, such as those with congenital long QT syndrome, cardiac disease, liver disease, electrolyte disturbance, or those taking drugs that can prolong QT interval, should avoid nonsedating antihistamines that are also capable of prolonging the QT interval. Many questions still need to be answered, such as the role of other potassium channels (IKs, ITo, and Iped) and the relative expression of various potassium channels in different individuals, which may be important in the pathogenesis of TdP with nonsedating antihistamines. There is also a lack of information on the cardiac actions of newer nonsedating antihistamines. The evidence so far indicates that the potential to cause ventricular arrhythmias is not a class effect and that loratadine, cetirizine, and fexofenadine are not associated with QT prolongation, TdP, or other ventricular arrhythmias. It is hoped that with a better understanding of the arrhythmogenic mechanism of nonsedating antihistamines, we will be able to identify patients at risk and prevent any cardiac toxicity associated with H1-antihistamines, and ultimately, death.

Action Potentials↗
PubMed2003

[Mesenteric traction syndrome during the operation of aneurysms of the abdominal aorta--histamine release and prophylaxis with antihistaminics].

Mesenteric traction syndrome occurs during abdominal surgery and is described as sudden tachycardia, hypotension and flush. Among other etiological factors, eventeration or mesenteric traction of the small intestine may cause histamine release from mesenteric mast cells. Therefore, our hypothesis was that mesenteric traction syndrome could be positively influenced by prophylactic administration of H1- and and H2-antihistamines. Seventeen male patients (ASA groups III-V, 48-78 years old) were investigated in a randomised double blind study during elective abdominal aortic aneurysm (AAA) repair; which, in our opinion, is one of the most standardised surgical procedures. Eight patients had pre-anaesthetic prophylaxis with 0.1 mg/kg BW dimetindene (H1-receptor antagonist) plus 5 mg/kg BW cimetidine (H2-receptor antagonist) diluted with 100 ml 0.9% NaCl, while 9 patients received a placebo (100 ml 0.9% NaCl). Anaesthesia and invasive haemodynamic monitoring were standardised in all patients. Haemodynamic parameters, plasma histamine concentrations and clinical symptoms were determined one min after skin incision (HS), and 5 and 20 min after mesenteric traction (5' EV and 20' EV). Statistical analyses were performed using the Student's t-test, the Mann-Whitney-U-test for continuous data and Chi2-test for incidences. The incidence of histamine release was 55.5% (5/9) in the placebo group vs. 37.5% (3/8) in the antihistamine group (p > 0.05, Chi2-test). Plasma histamine levels (mean +/- SD) were higher in the placebo group than in the antihistamine group at 5 and 20 min after mesenteric traction, but there was no statistical significance. Arrhythmias were significantly more frequent in the placebo group (6 times) than in the antihistamine group (none) (p = 0.005 Chi2-test). Systolic blood pressure was not statistically different between the groups (e.g. 5 min after mesenteric traction, mean +/- SD; placebo 111 +/- 20 mm Hg vs. antihistamines 119 +/- 35 mm Hg). In the placebo group, however, the haemodynamics only stabilised 5 min after mesenteric traction when anaesthetic gas concentration was repeatedly reduced and vasopressor/volume administration was increased (placebo group = 20 times vs. antihistamine group = 8 times (p = 0.001, Chi2-test). From these results we conclude that prophylactic administration of antihistamines reduces in particular the incidence of arrhythmias and the number of stabilising measures during mesenteric traction. Prophylaxis with H1- and H2-antihistamines may therefore be of perioperative benefit and should be considered in AAA surgery.

Aged↗
PubMed2006

Urticaria induced by antihistamines.

H1-antihistamines are commonly used drugs, and probably the most frequently used for allergic diseases. They are pharmacologic inverse agonists of histamine at H1 receptor sites and try to shift the equilibrium of this receptor toward the inactive state, preventing H1 response. A wide variety of adverse effects have been attributed to antihistamines, and they can exceptionally induce skin reactions. We report the case of a patient with several episodes of urticaria induced by different families of antihistamines - piperazines and piperidines. We performed skin prick tests (SPT), patch tests and oral challenges to different antihistamines. We found positive SPT to some antihistamines, and positive oral challenge in others with negative SPT. The route of sensitization remained unclear, and our patient could not finally tolerate any antihistamine after the oral challenges we performed. We support the hypothesis that antihistamines may shift the H1 histamine receptor to the active conformation instead of the inactive conformation, prompting adverse reactions after dosing. This is the first report of urticaria induced by different antihistamines in the same patient with positive SPT to several others.

Adult↗
PubMed1985

Antihistamine selection in patients with allergic rhinitis.

Seven hundred eighty-two patients diagnosed as having either seasonal allergic rhinitis or perennial allergic rhinitis in a solo allergy practice were given five different antihistamine products representing each of the five classes of antihistamines. The following products were evaluated for 2 weeks each: tripelennamine, diphenhydramine, chlorpheniramine, hydroxyzine, and trimeprazine. Symptoms and side effects were graded 0 to 4. The more troublesome side effects, graded 3 or 4, were tabulated. The antihistamine products in order of increasing frequency of significant side effects were: trimeprazine, chlorpheniramine, hydroxyzine, diphenhydramine, and tripelennamine. The order of antihistamine preference by the patients was chlorpheniramine (27%), diphenhydramine (22%), tripelennamine (20%), hydroxyzine (16%), and trimeprazine (14%). Only seven of 758 patients (less than 1%) were unable to find an acceptable antihistamine class. Patients remained on their antihistamine class of first choice 78% of the time after 1 year, 71% after 3 years and 51% after 5 years. The antihistamine pack provides a rational approach to antihistamine selection in patients with allergic rhinitis.

Chlorpheniramine↗
PubMed1987

Clinical pharmacodynamics of antihistamines.

Antihistamines act by competing with histamine for H1 or H2 histamine receptors on cell membranes. In addition, most of the common antihistamines bind other receptors and thus exert other pharmacologic actions. For all practical purposes, mast cells and basophils are the main physiologic sources of histamine, and the primary usefulness of antihistamines is in diseases characterized by excessive production and release of histamine by these two cell types. Experimental models have proven useful for evaluating antihistamine compounds in humans. In these model systems, a test drug may be employed to block one or more of the known effects of exogenously administered histamine or a histamine agonist. Or the release of endogenous histamine may be brought about in a controlled fashion by agents such as allergens, opiates, or compound 48/80, and the drug's effects on this process may then be measured. In the case of the central nervous system, unfortunately, such models are not available and other means of evaluation must be devised. The dose response and duration of action of orally administered antihistamines can be determined in a simple skin model by their blocking of the wheal and erythema (flare) resulting from an intradermal challenge with histamine, an allergen, or compound 48/80. Antihistamines can also be evaluated in urticaria induced by scratching or cold. Itching that commonly follows injection of histamine or an allergen into the skin is also inhibited by this class of drugs. Most of the commonly used antihistamines are effective in these models, which form the basis for evaluating antihistamines in the treatment of skin diseases. In the nose and conjunctiva, other model strategies are used.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗