Newer antihistaminic agents

Dual hypocretin receptor antagonism is more effective for sleep promotion than antagonism of either receptor alone

The hypocretin (orexin) system is involved in sleep/wake regulation, and antagonists of both hypocretin receptor type 1 (HCRTR1) and/or HCRTR2 are considered to be potential hypnotic medications. It is currently unclear whether blockade of either or both receptors is more effective for promoting sleep with minimal side effects. Accordingly, we compared the properties of selective HCRTR1 (SB-408124 and SB-334867) and HCRTR2 (EMPA) antagonists with that of the dual HCRTR1/R2 antagonist almorexant in the rat. All 4 antagonists bound to their respective receptors with high affinity and selectivity in vitro. Since in vivo pharmacokinetic experiments revealed poor brain penetration for SB-408124, SB-334867 was selected for subsequent in vivo studies. When injected in the mid-active phase, SB-334867 produced small increases in rapid-eye-movement (REM) and non-REM (NR) sleep. EMPA produced a significant increase in NR only at the highest dose studied. In contrast, almorexant decreased NR latency and increased both NR and REM proportionally throughout the subsequent 6 h without rebound wakefulness. The increased NR was due to a greater number of NR bouts; NR bout duration was unchanged. At the highest dose tested (100 mg/kg), almorexant fragmented sleep architecture by increasing the number of waking and REM bouts. No evidence of cataplexy was observed. HCRTR1 occupancy by almorexant declined 4–6 h post-administration while HCRTR2 occupancy was still elevated after 12 h, revealing a complex relationship between occupancy of HCRT receptors and sleep promotion. We conclude that dual HCRTR1/R2 blockade is more effective in promoting sleep than blockade of either HCRTR alone. In contrast to GABA receptor agonists which induce sleep by generalized inhibition, HCRTR antagonists seem to facilitate sleep by reducing waking “drive”.

Duration of the effect of astemizole on histamine-inhalation tests

The aim of the study was to investigate if astemizole, a new, long-acting antihistamine preparation, has an effect on histamine-inhalation tests and to assess the duration of action of this medication. The study included a group of 15 adult subjects with asthma in a clinically stable state. The subjects all demonstrated mild to severe bronchial hyperresponsiveness (geometric mean provocative concentration causing a 20% fall in FEV1 (PC20) histamine, 0.57; range, 0.20 to 4.7 mg/ml). The first part of the study was a double-blind, 7-day trial of astemizole (10 mg/day) or placebo, assigned in random order for the first eight subjects. The seven subjects entering the trial subsequently were administered active medication only. PC20 histamine was assessed on the 3 consecutive days before starting the trial, on the last day of medication, 3 days later, and once a week thereafter until PC20 returned to baseline. PC20 methacholine was also assessed before the trial and regularly thereafter to ensure functional stability. No significant changes in PC20 histamine were documented in the placebo-treated group, but the four subjects receiving active medication demonstrated marked changes in PC20 histamine (from a tenfold to a greater than 100-fold difference) (p = 0.001). There were no significant differences in changes in PC20 methacholine between the two treatment groups (p = 0.27). The duration of recovery of bronchial response to histamine in all 15 subjects ranged from 12 to 102 days (mean, 42 days) and was in some subjects, longer than the duration of the blocking effect of histamine reactivity found with skin testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of hay fever. Allergen avoidance and medication to control symptoms

Therapy for hay fever should begin with environmental control, because sometimes avoidance of allergens is all that is needed to adequately control symptoms. If not, useful medications include antihistamines, decongestants, combinations of the two, prescription nasal sprays, and allergy immunotherapy. The best method and correct dosage are important, both to ensure patient comfort and to prevent the side effects of allergic disorders.

Effect of topical levocabastine on allergic and non-allergic perennial rhinitis. A double-blind study, levocabastine vs. placebo, followed by an open, prospective, single-blind study on beclomethasone

Forty-four patients, with symptoms of nasal obstruction, sneezing, itching and/or rhinorrhea, were entered into a placebo-controlled, double-blind study to evaluate the clinical efficacy of a topical antihistamine drug, levocabastine, applied 4 times a day for 14 days. At the end of the treatment the placebo patients were treated with levocabastine and the levocabastine patients were treated with beclomethasone dipropionate in a single-blind design for another 14 days. This study showed that levocabastine is significantly more active than placebo with reference to nasal discharge and sneezing. Placebo application improved the symptom score. Levocabastine could not be proved to be more effective against nasal obstruction than placebo in the double-blind trial. In the single-blind set-up, levocabastine resulted in an additional improvement in the score for obstruction, after the placebo period. Although the allergic group tended to respond better, no statistically significant difference could be detected between allergic and non-allergic patients. After treatment with levocabastine, beclomethasone dipropionate administration could not improve the results for nasal discharge and sneezing. For nasal congestion, beclomethasone dipropionate proved to be superior to levocabastine.

Double-blind placebo-controlled study of loratadine, mequitazine, and placebo in the symptomatic treatment of seasonal allergic rhinitis

Loratadine is a long-acting H1 antagonist devoid of anticholinergic and sedative effects. A double-blind, placebo-controlled, parallel-group study was performed in 69 patients to compare efficacy and safety of loratadine and mequitazine. Patients allergic to grass pollens were randomly assigned to one of the three treatment groups and followed up to 2 weeks during the peak of the pollen season. Symptoms of allergic rhinitis were evaluated at baseline and after 3, 7, and 14 days of treatment by the physician with patients rating their response daily on diary cards. Both loratadine and mequitazine induced a significant relief of nasal symptoms when these were compared to placebo. Loratadine was found to be significantly superior to placebo after 3 days of treatment, whereas a significant improvement was only observed after 7 days in patients treated with mequitazine. For nonnasal symptoms, none of the two anti-H1 antagonist induced a significant improvement, and this lack of effect may be related to low symptoms at baseline. Loratadine did not induce more side effects than placebo. Loratadine can be considered to be an effective and safe anti H1 histamine with a rapid onset of action.

Astemizole: a long-acting, nonsedating antihistamine

Astemizole is a long-acting, highly selective histamine1-receptor antagonist with minimal central and anticholinergic effects. Comparison studies have shown astemizole to be equal or superior to currently available antihistamines, beclomethasone nasal spray, and cromolyn sodium in relieving allergic symptoms of seasonal and perennial allergic rhinitis. Other uses include treatment of allergic conjunctivitis and chronic urticaria. Astemizole is not as effective for treatment of acute allergic symptoms because of its delayed onset of action. Astemizole and its active metabolite, desmethylastemizole, have long elimination half-lives permitting once-daily dosing. The incidence of sedation is lower than with conventional antihistamines, but increased appetite and weight gain do occur. Astemizole should be useful for both maintenance and prophylactic therapy in patients with chronic allergic conditions who cannot tolerate the sedative or anticholinergic effects of conventional antihistamines.