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PubMedDate not supplied

Cardiovascular safety of second-generation antihistamines.

Reports of serious cardiac arrhythmia associated with some second-generation antihistamines have prompted concern for their prescription. This article reviews the nature of the adverse events reported and concludes that the blockade of potassium channels, particularly the subtype responsible for the rapid component of the delayed rectifier current (IKr), is largely responsible for such adverse cardiac events. Consequently, antihistamines with little or no interaction with these channels are expected to have the greatest safety margin. The main cardiac arrhythmia of concern is that of torsades de pointes, a potentially fatal phenomenon characterized by prolonged ventricular depolarization that manifests as a prolonged QT interval and polymorphic ventricular tachycardia, with twisting of the QRS complexes. Based on pre-clinical and clinical evidence, it appears that loratadine, cetirizine, and fexofenadine are safe from cardiac arrhythmia via the IKr channel, whereas astemizole and terfenadine have a propensity to cause ventricular tachyarrhythmias.

Animals↗
PubMed1985

Treatment of allergic rhinitis with a new selective H1 antihistamine: terfenadine.

The effectiveness of 60 mg b.i.d. of a novel antihistamine, terfenadine, was compared with an active control, 4 mg t.i.d. of chlorpheniramine, and placebo in 560 patients with seasonal allergic rhinitis. In contrast to the gradual decrease in seasonal symptoms observed over a 7 day period of study in placebo-treated patients, both antihistamines produced a prompt significant decrease in sneezing and rhinorrhea, and a gradual decrease in nasopharyngeal pruritus. Terfenadine-related sedation did not differ from that produced by the placebo and was less than the sedation produced by the active control.

Administration, Oral↗
PubMedDate not supplied

Methods of studying antihistamines.

A variety of ingenious methods have been devised to challenge and incite episodes of acute allergic rhinitis in susceptible individuals. These methods teach us much about basic mechanisms involved in the disease. There is some danger in using them for efficacy trials because antihistamines are only partially effective treatment for hay fever and the challenge administered could easily overcome the degree of protection. Additional studies may lead to a better understanding of the factors involved in challenges and hence, their usefulness in clinical testing. The out-patient trial design is successful in demonstrating efficacy in 40 to 60 per cent of trials. The field trial is 70 to 90 percent accurate in its findings. The clinical design of antihistamine trials has improved remarkably in the past 10 years. Because of the nature of the disadvantages discussed throughout this report, I would doubt that further improvements in design will occur in future years unless a substitute is found for subjective evaluations.

Animals↗
PubMedDate not supplied

Metachromatic reaction and antihistaminic drugs.

We studied the effect of antihistaminic substance on the dye-polysaccharide interaction, using a model in vitro system consisting of heparin-Na and the basic dye o-toluidine blue. The results are recorded on absorption curves in the visible range under standard and modified experimental conditions. We concluded that both histamine and antihistaminic drugs interact in vitro with mucopolysaccharide substances. The results are discussed on a pharmacological basis.

Color↗
PubMed1998

Suppressive effects of antihistaminic and/or anti-PAF agents on passive anaphylactic shock in mice sensitized with allogeneic monoclonal IgE and IgG1 antibodies and hyperimmune serum.

For the immunopharmacological characterization of murine passive anaphylactic shock, the effects of antihistaminics and/or anti-platelet-activating factor (anti-PAF) agents were studied on the shock mediated by allogeneic monoclonal IgE and IgG1 antibodies and hyperimmune serum. IgE antibody-mediated shock was strongly suppressed by cyproheptadine (10 mg/kg, ip) in every strain regardless of the age and sex of the mice and the presence or absence of a shock potentiator. As far as tested with CTS, DS, and B6D2F1 mice, IgE antibody-mediated shock was also suppressed by the other two antihistamines, triprolidine (10 mg/kg, ip) and oxatomide (100 mg/kg, po). This type of shock was not suppressed by an anti-PAF agent, CV-6209 (3.3 mg/kg, iv), when tested on aged CTS mice given no shock potentiator and young DS mice given a potentiator such as Bordetella pertussis organisms or DL-propranolol. IgG1 antibody-mediated shock was also suppressed by cyproheptadine in general except for CTS mice. Suppression in the DL-propranolol-treated DS and C3H/He mice was not very marked on sensitization with undiluted or slightly diluted IgG1 ascites but quite striking on sensitization with properly diluted ascites. In contrast with the effect of cyproheptadine, suppression by CV-6209 was obvious in aged CTS mice but not in young DL-propranolol-treated DS mice. The shock in DL-propranolol-treated DS mice sensitized with undiluted or slightly diluted ascites was completely abolished by the combined use of these two agents. These results suggest that histamine and/or PAF play a major role in IgE antibody- and IgG1 antibody-mediated shock. However, so far as tested in young DS mice, the shock mediated by hyperimmune serum differed in drug susceptibility from that mediated by the monoclonal antibodies. In the absence of shock potentiators, prevention was produced by cyproheptadine in the males which had been sensitized with the 1:4 or 1:8 dilution of the immune serum. In the presence of DL-propranolol, prevention was not produced even by the combined treatment with cyproheptadine and CV-6209. Therefore, it is likely that some mediators other than histamine and PAF, whose release is triggered by antibody isotypes other than IgE and IgG1, play a greater role for the shock mediated by hyperimmune serum than for the shock mediated by IgE or IgG1 antibody, especially in the presence of shock potentiators.

Anaphylaxis↗
PubMed1993

Non-traumatic rhabdomyolysis complicating antihistamine overdose.

Antihistamines are common over the counter medications which are frequently involved in overdoses. The usual clinical course is dominated by the anticholinergic affects of these agents; it includes significant autonomic and central nervous system effects and direct cardiac toxicity (1). We report a case of a suicide attempt in a young adult male where ingestion of the antihistamines diphenhydramine and doxylamine was complicated by non-traumatic rhabdomyolysis and acute renal failure.

Acute Kidney Injury↗
PubMed1992

Effects of antihistamines on cutaneous reactions and influx of eosinophils after local injection of PAF, kallikrein, compound 48/80 and histamine in patients with chronic urticaria and healthy subjects.

The effects of one week's daily treatment with dexchlorpheniramine (3 + 3 mg x 2) and loratadine (10 mg x 2) on the cutaneous reactions to putative mediators of urticarial reactions were studied in healthy subjects and in patients with chronic urticaria. Biopsy specimens were taken from skin with delayed reactions and studied immunohistochemically for the presence of eosinophilic cationic protein (ECP). In healthy subjects both antihistamines significantly decreased the weal and flare induced by histamine and the histamine releaser compound 48/80. They also reduced the flare seen after injection of PAF (platelet activating factor) and kallikrein. In patients with chronic urticaria the delayed reactions to PAF and kallikrein were larger than in healthy subjects. The immediate flare seen after injection of histamine, 48/80 and PAF, and the delayed reaction to 48/80, were significantly decreased by treatment with loratadine. No correlation was found between the clinical response and test reactions. In the group of healthy subjects, eosinophils were increased in the skin of all subjects after intradermal injection of 100 micrograms of PAF and in 50% after 1 microgram of PAF, but no eosinophils were seen after injection of 1 ng of PAF. In patients with chronic urticaria the eosinophils were increased at all sites where 1 ng of PAF had been injected and also at a limited number of sites of injection of histamine, 48/80, kallikrein and saline. Treatment with the antihistamines had no effect on the influx of eosinophils in the skin.

Adult↗
PubMed2000

Antihistamines and aircrew: usefulness of fexofenadine.

INTRODUCTION: The aim of this study was to establish whether fexofenadine hydrochloride, an antihistamine, modulates daytime sleepiness or performance. METHODS: The effects of fexofenadine (120, 180, and 240 mg) on digit symbol substitution, tracking, and vigilance tasks, and on objective (multiple sleep latency test) and subjective sleepiness, were studied in six healthy volunteers (two males, four females, aged 20-34 [mean 26.5] yr) from 1 h pre-ingestion to 8 h post-ingestion. The study was placebo-controlled and double-blind with a six-way cross-over design. The centrally acting antihistamine, promethazine (10 mg), was used as an active control to confirm the sensitivity of the experimental procedures. RESULTS: There were no changes in performance or sleepiness with any dose of fexofenadine at any time, compared with placebo. Promethazine, compared with both placebo and fexofenadine, impaired performance on the digit symbol substitution task (2.5 h post-ingestion), vigilance task (2.5-5h post-ingestion) and tracking task (2.5-3.5 h post-ingestion), increased objective sleepiness (1.5-2.5 h post-ingestion) and subjective sleepiness (1.5-8h post-ingestion). CONCLUSION: Consideration may be given to the clinical use of currently licensed doses of fexofenadine (120-180 mg) by individuals involved in skilled activity. Fexofenadine may be potentially useful for aircrew.

Adult↗
PubMed2000

[Pharma-clinics. How I treat ... pruritus by an antihistamine].

Pruritus is a symptom originating from multiple etiologies. Its pathogeny involves various mediators including histamine. Antihistamines, particularly the anti-H1 type can improve a few pruritic disorders. However, they do not compare with specific etiology based therapies. Choosing an antihistamine relies on the balance between efficacy and unwanted side effects which are sometimes serious.

Decision Making↗
PubMed1991

Is there a role for nonsedating antihistamines in motion sickness? Fallout from space research may soon benefit your patients.

The rotating chair test, a novel research technique for simulating motion sickness, is used to study the effect of nonsedating oral antihistamines in preventing or forestalling motion sickness. After receiving terfenadine, astemizole, doxepin, or placebo, four groups of male volunteers were rotated at accelerating speed, and they made head movements out of the axis of rotation until they perceived that vomiting would occur if additional head movements were made. Those pretreated with doxepin or terfenadine experienced a statistically significant prophylactic effect, as measured by increased tolerance to Coriolis stimulation. This suggests that selective peripheral H1 antihistamine action may protect against motion sickness.

Aerospace Medicine↗
PubMedDate not supplied

[H1 antihistaminics: can we precisely define the characteristics of the ideal molecule?].

The experience of the past twenty years in the field of H1 antihistamines prompts us to consider that these drugs are more dissimilar than has previously been reported in the scientific literature. In fact, the H1 antihistamines that are used in man seem to be effective, even if there are some differences in clinical efficacy. Nevertheless they may have marked differences as far as the following aspects are concerned: their possible binding to various biological targets, their pharmacokinetics, their metabolism and their volume of distribution. All these differences must be taken into consideration when judging the real quality of each of these drugs.

Animals↗
PubMed2002

Synthesis of new 2-substituted-[1,3,4]-oxadiazino-[6,5-b]-indoles with H1-antihistaminic, antimuscarinic and antimicrobial activity [corrected].

New 2-substituted-[1,3,4]-oxadiazino-[5,6-b]-indoles have been prepared and tested for their antibacterial, antifungal, H1-antihistaminic and antimuscarinic activities. Among them, compounds 5b, 5d, 5k exhibited higher H1-antihistaminic activity than pheniramine maleate. Compounds 5c, 5d showed higher antibacterial activity than ampicillin against Staphylococcus aureus and E. coli, respectively.

Animals↗
PubMed2002

[Influence of treating atopic dermatitis with oral antihistamine and topical steroids on selected parameters of cell and humoral immunity].

UNLABELLED: Pathogenesis of atopic dermatitis (AD) is multifactorial, therefore despite many different treatment protocols none of the available methods is effective enough. In the present study we analysed the effects of oral antihistamines and topical steroids on selected parameters of humoral (immunoglobulin levels) and cellular (lymphocyte proliferation index, granulocyte oxidative burst, lymphocyte phenotype CD4:CD8) immunity. These parameters were analysed in 34 AD subjects during the exacerbation of the disease and after 4 and 12 weeks of the treatment. RESULTS: Along with the clinical status improvement (change form 3.17 +/- 0.1 to 1.3 +/- 0.2; 0-4 scale; p < 0.001), total serum IgE levels decreased significantly from 1563 +/- 459 to 1266 +/- +/- 364 IU/ml (p < 0.05). Other immunoglobulin levels did not change. Total blood chemiluminescence in response to latex stimulation was relatively higher during exacerbation than during remission, but this difference was not significant (p = 0.1). Mean spontaneous or PMA stimulated chemiluminescence did not differ either. CD4:CD8 index decreased significantly during the treatment (from 2.7 +/- 0.3 to 1.8 +/- 0.2; p = 0.03). Lymphocyte proliferation in response to PHA was significantly lower during exacerbation than during remission (10.4 +/- 2.8 vs. 27.1 +/- +/- 5.2; p < 0.03) and the improvement was observed after first 4 weeks of the treatment reaching the levels found in healthy controls. Proliferation index in response to anti-CD3 mAb (OKT-3) was in turn significantly higher during exacerbation (19.1 +/- 3.4 vs. 11.2 +/- 2.0; p = 0.04). CONCLUSIONS: Oral antihistamine in combination with topical steroids leads to several significant changes in the immune parameters (IgE levels, CD4:CD8 and proliferation indexes) which may explain its high effectiveness in majority of patients with AD.

Administration, Oral↗
PubMed1977

Gastrin, antral g cells, and gastric acid in secretagogue-induced and antihistamine-inhibited duodenal ulcers.

In fasting control rats there was continuous basal gastric acid secretion, with a low plasma gastrin and antral G-cells full or immunofluroescent gastrin. After subcutaneous infusion of the gastric secretagogues, pentagastrin + carbachol, there was a six-hour period of gastric hypersecretion, but no change in plasma and G-cell gastrin. Pretreatment with the antihistamine derivative, Pfizer UK-9040, decreased both basal and stimulated acid secretion, whereas plasma gastrin levels increased and the antral G-cells were emptied of gastrin. These results suggest that this antihistamine derivative decreases gastric acid secretion by a direct action on the parietal cells and not by reducing gastrin release from the G-cells. The increased release of gastrin from the G-cells may be secondary to decreased gastric acid production, or more probably by a direct stimulation of the antral G-cells.

Animals↗
PubMed1992

Pharmacodynamics and pharmacokinetics of mizolastine (SL 85.0324), a new nonsedative H1 antihistamine.

The antihistaminic activity, clinical safety, and pharmacokinetics of mizolastine (SL 85.0324) were studied in a 5-way, double-blind crossover study of ten healthy volunteers with doses of 1 to 75 mg. Inhibition of the histamine-induced wheal and flare showed clear dose-dependent antihistaminic activity beginning from the 2-mg dose with a maximum attained between 10 and 20 mg. The onset of action was rapid (one hour) and the effect persisted for more than 24 hours after a 10-mg dose or more. Mizolastine was well tolerated at doses up to 75 mg; subjective and objective signs of transient sedative activity were not observed at doses below 30 mg. The pharmacokinetic profile (rapid absorption with Tmax congruent to 1 h and elimination T1/2 of about eight hours) parallels the pharmacodynamic activity. Within the considered dose range, the pharmacokinetics was linear with no saturation phenomena.

Adult↗
PubMed1992

Antihistamine activity of Bryophyllum calycinum.

1. The juice obtained by pressing the leaves of Bryophyllum calycinum (Crassulaceae) exhibited histamine-blocking activity. 2. The juice contains flavonoid compounds, carbohydrates and mineral salts. A flavonoid fraction (fraction B) obtained by partitioning the juice between n-butanol and water contained the substance responsible for the antihistamine activity. 3. When assayed on the isolated guinea pig ileum, 50 mg/ml juice and 0.15 mg/ml fraction B produced parallel and concentration-dependent rightward displacement of the concentration-response curve to histamine (EC50 (FL): 1.30 (0.26-5.28) x 10(-7) M, 15.80 (5.90-23.30) x 10(-7) M, 12.50 (7.62-14.90) x 10(-7) M, in the absence and presence of 50 mg/ml juice and 12 mg/ml fraction B, respectively) apparently in a competitive manner. The antagonism was specific for histamine, i.e., did not modify the response to acetylcholine, KCl and BaCl2 and was reversible upon washing. Vascular permeability responses of rats to intracutaneous 1.0, 5.0 or 10.0 micrograms histamine were decreased by about 20-25% in animals pretreated with 4 ml/kg of juice or with 12 mg/kg fraction B. The juice (4 ml/kg) protected guinea pigs from death by asphyxia induced by 5 mg histamine and the protection lasted at least 1 h. 4. However, since the juice was ineffective in protecting the gastric mucosa from histamine-induced ulceration, we conclude that the antihistamine effect of the juice and fraction B was produced by blockade of H1 and not H2 receptors.

Animals↗
PubMed1992

Clinical experience with non-sedating antihistamines in paediatric allergic rhinitis.

This paper reviews all clinical studies involving the use of astemizole in children. The indications of seasonal allergic rhinitis, perennial rhinitis and various allergic disorders were considered in a total of 21 studies (1,008 patients). Reference compounds were placebo and other antihistamines, such as chlorpheniramine and terfenadine. Astemizole and other antihistamines were effective in the treatment of these disorders with a more favourable result for those treated with astemizole. Astemizole appeared very satisfactory as regards laboratory data and absence of side effects.

Adolescent↗