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At least 829 records · Page 46Linked to original sources
PubMed1994

In vitro effects of H1-antihistamines on histamine and PGD2 release from mast cells of human lung, tonsil, and skin.

Mast cells from different anatomic sites differ in cytochemistry and response to various secretory stimuli. We have investigated whether responsiveness to the second-generation H1-receptor antagonists, which are important first-line drugs for the relief of symptoms in patients with chronic urticaria and allergic rhinoconjunctivitis, also differs according to the site of origin of mast cells. The effects of terfenadine, ketotifen, and cetirizine were therefore examined in relation to the IgE-dependent release of histamine and prostaglandin D2 (PGD2) from dispersed human lung, tonsil, and skin mast cells. Terfenadine had a biphasic effect on lung and skin mast cells: at low concentrations, a concentration-dependent inhibition of histamine release from lung and skin mast cells was observed, whereas at higher concentrations the drug stimulated mediator release. Even at a high concentration, terfenadine inhibited mediator release from tonsil mast cells. Ketotifen had low potency as an inhibitor of mediator release from lung and tonsil mast cells. In skin mast cells, no inhibition of mediator release was observed below 1.0 microM, and above that concentration it induced mediator release. Cetirizine, a much less lipophilic drug than the others tested, did not induce mediator release from mast cells even at concentrations up to 100 microM. This drug showed concentration-dependent inhibition of IgE-dependent mediator release from lung and tonsil mast cells only. Our results show that human mast cells are heterogeneous with respect to modulation of mediator release by these H1-antihistamines. In particular, differences were observed between skin mast cells and those dispersed from lung and tonsils.

Cetirizine↗
PubMed1995

Antihistamine effects on actual driving performance in a standard test: a summary of Dutch experience, 1989-94.

The review summarizes the major results of eight double-blind, placebo-controlled, volunteer studies undertaken by three independent institutions for showing the effects on actual driving performance of "sedating" and "nonsedating" antihistamines (respectively, triprolidine, diphenhydramine, clemastine and terfenadine, loratadine, cetirizine, acrivastine, mizolastine, and ebastine). A common, standardized test was used that measures driving impairment from vehicular "weaving" (i.e., standard deviation of lateral position (SDLP)). Logical relationships were found between impairment and dose, time after dosing, and repeated doses over 4-5 days. The newer drugs were generally less impairing, but differences existed among their effects, and none was unimpairing at doses 1-2x the currently recommended levels. One or possibly two of the newer drugs possessed both performance-enhancing and -impairing properties, depending on dose, suggesting two mechanisms of action.

Automobile Driving↗
PubMed1997

Onset of action in the nasal antihistaminic effect of cetirizine and loratadine in patients with allergic rhinitis.

Several studies have compared the cutaneous efficacy of cetirizine and loratadine and their onset of action. We assessed the nasal effect of these two antihistamines in a randomized, double-blind, crossover, placebo-controlled trial in order to compare objectively their efficacy and onset of action in the noses of patients with allergic rhinitis. Nasal challenge was performed by nebulization of increasing doubling doses of histamine (0, 0.04-1.28 mg/nostril) in 12 patients (eight men, four women, aged 22-39 years). Nasal airway resistance (NAR) was measured by posterior rhinomanometry either 1.5 h or 4 h after intake of cetirizine (10 mg), loratadine (10 mg), or placebo. Baseline NAR was identical between all study days (2.60-2.88 cmH2O.l-1.s). One and a half hours after intake, the increase in NAR induced by histamine was significantly reduced by both cetirizine and loratadine in contrast to placebo. However, with cetirizine the nasal obstruction was significantly lower than with loratadine (P < 0.05). Four hours after intake, a similar inhibition of the nasal obstruction caused by histamine was observed with both cetirizine and loratadine (P < 0.05). In conclusion, this study found cetirizine and loratadine to have similar nasal efficacy at therapeutic dosage 4 h after intake, whereas cetirizine was more effective than loratadine 1.5 h after intake. In agreement with the results observed in the skin, our study suggests a more rapid onset of action of cetirizine in the nose in allergic rhinitis.

Adult↗
PubMed1997

Can an antihistamine delay appearance of hay fever symptoms when given prior to pollen season?

Mizolastine is a new, nonsedating antihistamine providing satisfactory symptom relief in allergic conditions. The purpose of this study was to determine whether the onset of hay fever symptoms could be delayed in patients known to suffer seasonal allergic rhinoconjunctivitis symptoms if mizolastine was given before the pollen season. This double-blind study involved 342 patients, randomly allocated to once-daily 10 mg mizolastine (n = 115), once-daily 120 mg terfenadine (n = 116), or placebo (n = 111) groups. All patients started treatment on 1 May, before the onset of the grass pollen season. The prophylactic effect of test drugs was assessed on their ability to delay the time to the first hay fever crisis of the season, which was defined by the occurrence of one of the following events: use of rescue medication, study withdrawal because of treatment failure, or total diary symptom score over 18. Active treatments prolonged the time to the first crisis by approximately 1 week (mizolastine 55 days, terfenadine 57 days) in comparison with placebo (50 days) (survival curve analysis: Logrank test, P = 0.01; Wilcoxon test, P = 0.03). Tolerability was satisfactory and comparable between groups. Thus, mizolastine can be safely used to delay and to treat symptoms of seasonal allergic rhinitis.

Adult↗
PubMed1958

Sensitization of the heart and nictitating membrane of the cat to sympathomimetic amines by antihistamine drugs.

Sensitization to the cardio-accelerator action of adrenaline and noradrenaline by five antihistamines was examined on the acutely denervated heart of the cat. Antazoline (Antistin), chlorcyclizine and promethazine (Phenergan) increased the cardio-accelerator responses to both amines equally. Mepyramine (Anthisan) increased noradrenaline more than adrenaline action. Diphenhydramine (Benadryl) resembled cocaine in potentiating the responses to noradrenaline but not to adrenaline.On the nictitating membrane mepyramine caused sensitization to the actions of adrenaline, noradrenaline and tyramine, an effect similar to that of chronic preganglionic denervation. Diphenhydramine enhanced the action of noradrenaline more than that of adrenaline and had little effect on tyramine action, giving a sensitization which bears a greater resemblance to the type caused by cocaine or chronic postganglionic denervation.It is suggested that two distinct mechanisms are required to account for the phenomena of sensitization.

Amines↗
PubMed1999

Block of HERG potassium channels by the antihistamine astemizole and its metabolites desmethylastemizole and norastemizole.

INTRODUCTION: The selective H1-receptor antagonist astemizole (Hismanal) causes acquired long QT syndrome. Astemizole blocks the rapidly activating delayed rectifier K+ current I(Kr) and the human ether-a go-go-related gene (HERG) K+ channels that underlie it. Astemizole also is rapidly metabolized. The principal metabolite is desmethylastemizole, which retains H1-receptor antagonist properties, has a long elimination time of 9 to 13 days, and its steady-state serum concentration exceeds that of astemizole by more than 30-fold. A second metabolite is norastemizole, which appears in serum in low concentrations following astemizole ingestion and has undergone development as a new antihistamine drug. Our objective in the present work was to study the effects of desmethylastemizole, norastemizole, and astemizole on HERG K+ channels. METHODS AND RESULTS: HERG channels were expressed in a mammalian (HEK 293) cell line and studied using the patch clamp technique. Desmethylastemizole and astemizole blocked HERG current with similar concentration dependence (half-maximal block of 1.0 and 0.9 nM, respectively) and block was use dependent. Norastemizole also blocked HERG current; however, block was incomplete and required higher drug concentrations (half-maximal block of 27.7 nM). CONCLUSIONS: Desmethylastemizole and astemizole cause equipotent block of HERG channels, and these are among the most potent HERG channel antagonists yet studied. Because desmethylastemizole becomes the dominant compound in serum, these findings support the postulate that it becomes the principal cause of long QT syndrome observed in patients following astemizole ingestion. Norastemizole block of HERG channels is weaker; thus, the risk of producing ventricular arrhythmias may be lower. These findings underscore the potential roles of some H1-receptor antagonist metabolites as K+ channel antagonists.

Astemizole↗
PubMed2001

Antihistamine agent Dimebon as a novel neuroprotector and a cognition enhancer.

Dimebon, launched earlier in Russia as an antihistamine drug, was evaluated as a representative of a new generation of anti-Alzheimer's drugs that have two beneficial actions: (1) to alleviate symptoms, and (2) to prevent progression of the disease. The drug demonstrated cognition and memory-enhancing properties in the active avoidance test in rats treated with the neurotoxin AF64A, which selectively destroys cholinergic neurons. Dimebon protected neurons in the cerebellum cell culture against the neurotoxic action of beta-amyloid fragment (A beta 25-35, EC50 = 25 microM). In vitro, Dimebon displayed Ca(2+)-blocking properties (IC50 = 57 microM, on isolated rat ileum intestine) and pronounced anticholinesterase activity (IC50 = 7.9 microM and 42 microM for butyrylcholine esterase and acetylcholine esterase, respectively). It also exhibited strong anti-NMDA activity in the prevention of NMDA-induced seizures in mice (EC50 = 42 +/- 6 mg/kg i.p.). A beneficial effect of Dimebon in the therapy of Alzheimer's disease was demonstrated in a pilot clinical trial performed in the Moscow Center of Gerontology. Fourteen patients who participated in the trial were evaluated for their state of personality and for the severity of the disease. The evaluation included orientation (space, place, time, and patient personality), memory for the past and present, life in present, speech, irritability, and so forth. During and after the eight-week therapy with Dimebon, cognitive and self-service functions of patients improved significantly, and psychopathic symptoms, anxiety, depression, tearfulness, and headache were substantially diminished. The results of these studies suggest Dimebon as a new candidate for the therapy of Alzheimer's-like disorders.

Aged↗
PubMed1975

The surface activity of some antihistamines at the air-solution interface.

The surface activity of some antihistamines at the air-solution interface has been examined. Change of the counterion associated with the drug from chloride to maleate or chloro-theophyllinate considerably decreased the critical micelle concentration and increased the surface activity. The effect on surface activity of changes in the nature of the hydrophobic and hydrophilic groups have also been evaluated.

Air↗
PubMed1975

Aggregation of antihistamines in aqueous solution. The effect of electrolyte on the miscellar properties of some diphenylmethane derivatives.

The effect of sodium chloride on the micellar properties of the antihistamines, dephenhydramine hydrochloride, bromodiphenhydramine hydrochloride, chlorcyclizine hydrochloride and diphenylpyraline hydrochloride in aqueous solution has been investigated by light scattering and viscometric methods. The drugs behaved as typical ionic surfactants showing an increase in aggregation number and decrease in critical micelle concentration as the electrolyte concentration was increased over the range 0.05 to 0.154 mol kg-minus1. A linear relation between log critical micelle concentration and log counterion concentration was established, from which values of the degree of ionization and the free energy of micellization were calculated. The intrinsic viscosity was decreased by the addition of electrolyte and this has been attributed to a decrease in micellar hydration due to a removal of hydrogen-bonded water.

Benzhydryl Compounds↗
PubMed1984

Increased brain uptake of morphine in the presence of the antihistamine tripelennamine.

Disposition of [6 3H (N)]morphine in plasma, brain and liver of rats was studied 15 min after intravenous injection of either a 2 mg kg-1 dose of morphine or a combination of the same dose of morphine with a 6 mg kg-1 dose of tripelennamine. The concentrations of morphine in brain and the brain to plasma morphine ratios in animals receiving the combination of drugs concurrently were significantly higher than those in the control morphine group. No significant differences were seen in the morphine or morphine metabolite concentrations in plasma and liver or liver to plasma morphine concentration ratios in the 2 groups. Data suggest that pharmacokinetic factors play a role in the potentiation of opiate effects by antihistamine on concurrent i.v. administration of the two drugs.

Animals↗
PubMed1988

Antihistaminic and anticholinergic activities of mequitazine in comparison with clemizole.

The antihistamine and anticholinergic properties of mequitazine have been investigated and compared with those of clemizole. Both mequitazine and clemizole antagonized the effect of histamine in guinea-pig ileum competitively, the pA2 values calculated by Schild plot were 9.95 +/- 0.44 for mequitazine and 10.54 +/- 0.44 for clemizole. Mequitazine at 10(-7) M produced a parallel shift of the dose-response curve to acetylcholine in the rat duodenum, clemizole and the lower doses of mequitazine failed to modify the effect of acetylcholine. The potency of mequitazine and clemizole as H1-histamine blockers is similar, but only mequitazine at highest concentration used showed anticholinergic activity.

Acetylcholine↗
PubMed1990

Antihistaminic activity of pulegone on the guinea-pig ileum.

Pulegone, a natural monoterpene compound, has an antihistamine effect on guinea-pig ileum. Its antagonism is of the competitive type (PA2 = 6.35) like that of mepyramine and dexchlorpheniramine, two H1-antagonists, with PA2 values of 10.15 and 8.74, respectively.

Animals↗
PubMed1974

Antihistamines block radiation-induced taste aversions.

When rats are treated with an antihistamine prior to being given sublethal doses of ionizing radiation, the formation of a conditioned saccharin aversion is completely inhibited. A profound aversion could be conditioned with histamine diphosphate as the aversive stimulus. The increase in histamine production after radiation exposure represents the physiological basis of radiation-induced taste aversions.

Animals↗
PubMed1980

Liver tumors induced in rats by oral administration of the antihistaminic methapyrilene hydrochloride.

The antihistaminic over-the-counter drug methapyrilene hydrochloride, mixed with food at a concentration of 0.1 percent, was administered to 50 male and 50 female Fischer rats. A second group of 50 male and 50 female rats was given the same treatment together with 0.2 percent of sodium nitrite added to the food. Almost all of the rats in both groups developed liver neoplasms, mainly hepatocellular carcinomas and cholangiocarcinomas. The first rat died with a liver neoplasm at the 43rd week. Over 50 percent of the rats in both groups had metastases from the carcinomas of the liver to distant organs. Control rats treated with nitrite only, or untreated, did not develop liver neoplasms. There was no discernible effect of nitrite on the carcinogenicity of methapyrilene hydrochloride.

Aminopyridines↗
PubMed1996

Fungal biotransformation of the antihistamine azatadine by Cunninghamella elegans.

The metabolism of the antihistamine azatadine by the zygomycete fungus Cunninghamella elegans ATCC 9245 was investigated. Within 72 h from the addition of the drug to 48-h-old cultures grown in Sabouraud dextrose broth, 95% of azatadine was biotransformed. Two major metabolites, 7-hydroxyazatadine (25%) and 8-hydroxyazatadine (50%), and two minor metabolites, N-desmethylazatadine and 9-hydroxyazatadine, were isolated by high-performance liquid chromatography and characterized by mass spectrometric and proton nuclear magnetic resonance spectroscopic analyses.

Biotransformation↗
PubMed2000

Sedation with "non-sedating" antihistamines: four prescription-event monitoring studies in general practice.

OBJECTIVES: To investigate the frequency with which sedation was reported in post-marketing surveillance studies of four second generation antihistamines: loratadine, cetirizine, fexofenadine, and acrivastine. DESIGN: Prescription-event monitoring studies. SETTING: Prescriptions were obtained for each cohort in the immediate post-marketing period. SUBJECTS: Event data were obtained for a total of 43 363 patients. MAIN OUTCOME MEASURES: Reporting of sedation or drowsiness. RESULTS: The odds ratios (adjusted for age and sex) for the incidence of sedation were 0.63 (95% confidence interval 0.36 to 1.11; P=0.1) for fexofenadine; 2.79 (1.69 to 4.58; P<0.0001) for acrivastine, and 3.53 (2.07 to 5.42; P<0.0001) for cetirizine compared with loratadine. No increased risk of accident or injury was evident with any of the four drugs. CONCLUSIONS: Although the risk of sedation was low with all four drugs, fexofenadine and loratadine may be more appropriate for people working in safety critical jobs.

Adolescent↗
PubMed2002

Oral antihistamines for allergic disorders.

There are now 17 oral H1-antihistamines available in the UK for treating allergic disorders. Here, we assess their use in treating hayfever, urticaria and pruritus, and consider whether any hold particular advantages.

Administration, Oral↗