Evaluation of the CNS properties of SCH 29851, a potential non-sedating antihistamine

Ultrasensitive TLC determination of montlukast and loratadine mixture in human plasma utilizing fluorescence detection at dual pH values: Toward attaining separate maximum fluorescence intensity

A novel selective and highly sensitive TLC densitometric method with reflectance/fluorescence detection was developed to separate and quantify montlukast (MONT) and loratadine (LOR). Separation of the studied drugs was performed on precoated silica gel TLC plates using chloroform-ethyl acetate (8 :2 v/v) as a mobile phase. MONT quantification was carried out by measuring emission using 400 nm optical filter after excitation at 340 nm. Enhancement of the week LOR fluorescence was performed through adequate spraying the chromatograms with 0.2 M perchloric acid leading to enhancing sensitivity by 17 folds compared to the reported HPTLC methods with absorbance detection. The scanner was set at 275 nm excitation wavelength and 400 nm optical filter. Detection of both drugs on the same plate separately at different pH conditions was utilized for the first time. Maximum fluorescence was achieved for each of them and this enhances detection sensitivity for both drugs. The linear regression analysis data of the studied drugs produced a good linear relationship with correlation coefficients of 0.996 for MONT and 0.998 for LOR over the concentration range of 6 - 150 ng/band for MONT and 15 - 120 ng/band for LOR. Limit of detection values were 1.7 and 4.5 ng /band for MONT and LOR respectively. The developed method enabled the detection of MONT and LOR in human plasma samples within linear concentrations ranged from 7 to 140 ng/ band and 16 to 50 ng/ band with detection limits of 1.9 and 4.8 ng/band for MONT and LOR respectively. The analytical performance of the proposed method was evaluated according to the International Council for Harmonization (ICH). The method was successfully applied for the analysis of the studied drugs in spiked human plasma and good recovery percentages were obtained indicating that there is no interference from plasma constituents. Therefore the method can be applied for in vivo analysis and pharmacokinetic study.

Development of a Conformational Histamine H3 Receptor Biosensor for the Synchronous Screening of Agonists and Inverse Agonists

The histamine H₃ receptor (H₃R) represents a highly attractive drug target for the treatment of various central nervous system disorders, but the discovery of novel H₃R targeting compounds relies on the assessment of highly amplified intracellular signaling events that do not only reflect H₃R modulation and carry the risk of high false-positive and -negative screening rates. To address these limitations, we designed an intramolecular H₃R biosensor based on the principle of bioluminescence resonance energy transfer (BRET) that reports the receptor’s real-time conformational dynamics and provides an advanced tool to screen for both H₃R agonists and inverse agonists in a live cell screening-compatible assay format. This conformational G-protein-coupled receptor (GPCR) sensor allowed us to characterize the pharmacological properties of known and new H₃ receptor ligands with unprecedented accuracy. Interestingly, we found that one newly developed H₃ receptor ligand possesses even stronger inverse agonistic activity than reference H₃R inverse agonists including the current gold standard pitolisant. Taken together, we describe here the design and validation of the first screening-compatible H₃R conformational biosensor that will aid in the discovery of novel H₃R ligands and can be employed to gain deeper insights into the (in-)activation mechanism of this highly attractive drug target.

New H1-Receptor Antagonists: A Review

The new H1-receptor antagonists such as astemizole, cetirizine, loratadine, levocabastine, ketotifen, and azelastine have diverse pharmacokinetics, pharmacodynamics, and potency. Astemizole, for example, is the most long-acting of the new drugs and is not suitable for sporadic use. Cetirizine, the carboxylic acid metabolite of hydroxyzine, unlike other H1-receptor antagonists, is minimally metabolized in the body and is primarily excreted in unchanged form in the urine. Levocabastine is the most potent of the new drugs and can be applied topically to the conjunctivae or to the nasal mucosa for relief of allergic rhinoconjunctivitis. Ketotifen and azelastine have well-described antiallergic effects in addition of their antihistaminic effects. None of the new H1-receptor antagonists is any more effective in relieving nasal congestion than the first-generation H1-receptor antagonists are. Most, but not all, of the new H1-receptor antagonists lack anticholinergic effects and are relatively nonsedating.

Loratadine: A Potent, Nonsedating, and Long-Acting H1 Antagonist

Loratadine, a nonclassical selective, peripheral H1-receptor antagonist has undergone extensive preclinical studies and clinical trials in over 6,000 patients. In the treatment of allergic rhinitis, loratadine has efficacy equivalent to clemastine, terfenadine, astemizole, and mequitazine. Its duration of action is 18–24 hours making once daily dosing practical. Loratadine is virtually devoid of sedating or other CNS effects.

A Double-Blind Study of the Effects of Loratadine versus Placebo on the Performance of Pilots

The effects of a single 10-mg dose of loratadine on the performance of commercial and military pilots was compared with placebo in this randomized double-blind trial. Performance was evaluated by flight simulator tests carried out before and after pilots received active drug or placebo. Simulators were specific for the DC-10, Boeing 747, and AT-26 Xavante fighter aircraft; all reproduced the respective conditions of flight. Pilots’ performance, rated by observers blinded to the test, was judged to be within operating standards. The findings were compatible with those of previous studies that found no sedating effects of loratadine that would impact adversely on automobile driving performance. This and other studies reinforce the pharmacokinetic observation that loratadine does not cross the blood-brain barrier, does not cause sedation, and, therefore, does not impair functional ability. These findings strongly suggest that loratadine use is compatible with the activity of pilots.

Loratadine and analogues: discovery and preliminary structure-activity relationship of inhibitors of the amino acid transporter B(0)AT2

B(0)AT2, encoded by the SLC6A15 gene, is a transporter for neutral amino acids that has recently been implicated in mood and metabolic disorders. It is predominantly expressed in the brain, but little is otherwise known about its function. To identify inhibitors for this transporter, we screened a library of 3133 different bioactive compounds. Loratadine, a clinically used histamine H1 receptor antagonist, was identified as a selective inhibitor of B(0)AT2 with an IC50 of 4 μM while being less active or inactive against several other members of the SLC6 family. Reversible inhibition of B(0)AT2 was confirmed by electrophysiology. A series of loratadine analogues were synthesized to gain insight into the structure-activity relationships. Our studies provide the first chemical tool for B(0)AT2.

Orexin receptor antagonist-induced sleep does not impair the ability to wake in response to emotionally salient acoustic stimuli in dogs

The ability to awaken from sleep in response to important stimuli is a critical feature of normal sleep, as is maintaining sleep continuity in the presence of irrelevant background noise. Dual orexin receptor antagonists (DORAs) effectively promote sleep across species by targeting the evolutionarily conserved wake-promoting orexin signaling pathway. This study in dogs investigated whether DORA-induced sleep preserved the ability to awaken appropriately to salient acoustic stimuli but remain asleep when exposed to irrelevant stimuli. Sleep and wake in response to DORAs, vehicle, GABA-A receptor modulators (diazepam, eszopiclone and zolpidem) and antihistamine (diphenhydramine) administration were evaluated in telemetry-implanted adult dogs with continuous electrocorticogram, electromyogram (EMG), electrooculogram (EOG), and activity recordings. DORAs induced sleep, but GABA-A modulators and antihistamine induced paradoxical hyperarousal. Thus, salience gating studies were conducted during DORA-22 (0.3, 1, and 5 mg/kg; day and night) and vehicle nighttime sleep. The acoustic stimuli were either classically conditioned using food reward and positive attention (salient stimulus) or presented randomly (neutral stimulus). Once conditioned, the tones were presented at sleep times corresponding to maximal DORA-22 exposure. In response to the salient stimuli, dogs woke completely from vehicle and orexin-antagonized sleep across all sleep stages but rarely awoke to neutral stimuli. Notably, acute pharmacological antagonism of orexin receptors paired with emotionally salient anticipation produced wake, not cataplexy, in a species where genetic (chronic) loss of orexin receptor signaling leads to narcolepsy/cataplexy. DORA-induced sleep in the dog thereby retains the desired capacity to awaken to emotionally salient acoustic stimuli while preserving uninterrupted sleep in response to irrelevant stimuli.

Effects of histamine on spontaneous neuropathic pain induced by peripheral axotomy

The present study was designed to investigate the effects of histamine on spontaneous neuropathic pain (NP) induced by peripheral axotomy. Rats and mice were subjected to complete transection of the left sciatic and saphenous nerves to induce spontaneous NP (the neuroma model). Rats were then treated with drugs once daily for 30 days (histidine and loratadine, i.p.) or 21 days (histamine, i.c.v.). Autotomy behavior was scored daily until day 50 post-operation (PO). On days 14 to 21 PO, some rats in the control group were subjected to single-fiber recording. Autotomy behavior was also monitored daily in histidine decarboxylase (the key enzyme for histamine synthesis) knockout (HDC(-/-)) and wild-type mice for 42 days. We found that both histidine (500 mg/kg) (a precursor of histamine that increases histamine levels in the tissues) and histamine (50 μg/5 μL) significantly suppressed autotomy behavior in rats. HDC(-/-) mice lacking endogenous histamine showed higher levels of autotomy than the wild-type. In addition, the analgesic effect of histidine was not antagonized by loratadine (a peripherally-acting H1 receptor antagonist), while loratadine alone significantly suppressed autotomy. Electrophysiological recording showed that ectopic spontaneous discharges from the neuroma were blocked by systemic diphenhydramine (an H1 receptor antagonist). Our results suggest that histamine plays an important role in spontaneous NP. It is likely that histamine in the central nervous system is analgesic, while in the periphery, via H1 receptors, it is algesic. This study justifies the avoidance of a histamine-rich diet and the use of peripherally-acting H1 receptor antagonists as well as agents that improve histamine action in the central nervous system in patients with spontaneous NP.

Predicting and establishing the clinical efficacy of a histamine h(1)-receptor antagonist : desloratadine, the model paradigm

Antihistamines are well established as a mainstay for treating allergic diseases, including seasonal and perennial allergic rhinitis as well as other conditions, such as chronic idiopathic urticaria. The development of new antihistamines is a multistage process that includes in vitro and in vivo assessments of the antihistaminic, anti-inflammatory and antiallergic properties of new therapies. Results of these assessments are critical for predicting and establishing the clinical efficacy of an antihistamine. The focus of this article is to review the investigational methods used to assess the efficacy, safety and tolerability of newer histamine H(1)-receptor antagonists. Desloratadine, a new-generation H(1)-receptor antagonist, was chosen to illustrate the use of this model paradigm. Data obtained from two large observational studies are presented, confirming results obtained from clinical trials that the in vitro inhibition of release of inflammatory mediators such as histamine, prostaglandins, leukotrienes and the reduction of secretion of cytokines such as IL-4 and IL-13 at physiological concentrations is reflected in increased efficacy, particularly upon nasal obstruction. A recent discovery that des- loratadine inhibits nuclear factor-kappaB may be the underlying explanation for much of this extra anti-inflammatory activity.

Involvement of the brain histaminergic system in addiction and addiction-related behaviors: a comprehensive review with emphasis on the potential therapeutic use of histaminergic compounds in drug dependence

Neurons that produce histamine are exclusively located in the tuberomamillary nucleus of the posterior hypothalamus and send widespread projections to almost all brain areas. Neuronal histamine is involved in many physiological and behavioral functions such as arousal, feeding behavior and learning. Although conflicting data have been published, several studies have also demonstrated a role of histamine in the psychomotor and rewarding effects of addictive drugs. Pharmacological and brain lesion experiments initially led to the proposition that the histaminergic system exerts an inhibitory influence on drug reward processes, opposed to that of the dopaminergic system. The purpose of this review is to summarize the relevant literature on this topic and to discuss whether the inhibitory function of histamine on drug reward is supported by current evidence from published results. Research conducted during the past decade demonstrated that the ability of many antihistaminic drugs to potentiate addiction-related behaviors essentially results from non-specific effects and does not constitute a valid argument in support of an inhibitory function of histamine on reward processes. The reviewed findings also indicate that histamine can either stimulate or inhibit the dopamine mesolimbic system through distinct neuronal mechanisms involving different histamine receptors. Finally, the hypothesis that the histaminergic system plays an inhibitory role on drug reward appears to be essentially supported by place conditioning studies that focused on morphine reward. The present review suggests that the development of drugs capable of activating the histaminergic system may offer promising therapeutic tools for the treatment of opioid dependence.

Saliva secretion in patients with allergic rhinitis

BACKGROUND

Allergic rhinitis is manifested by watery discharge; however its clinical effect on the watery volume in the oral cavity is unknown. In addition, the low incidence of dry mouth due to treatment with the new generation antihistamines is based on subjective patients' reports only. This study aimed to examine the effect of loratadine and fexofenadine on the salivary gland function in patients diagnosed with allergic rhinitis compared to untreated allergic patients and healthy individuals.

METHODS

A comparative observational study assessed parameters related to the patients' perception of dry mouth as well as clinically observed parameters in fexofenadine-treated patients (group A) and in loratadine-treated patients (group B). Allergic patients without pharmacological treatment (group C) and healthy individuals (group D) served as a double control in order to evaluate the effect of allergy itself on dry mouth. A total of 36 patients were enrolled.

RESULTS

Patients in groups A and C reported the highest intensity of xerostomia. Sialometry values were significantly lower in these 2 groups compared to the healthy controls (p = 0.02 and 0.03, respectively). Average sialometry was over 0.2 ml/min in all groups and subjective dry mouth sensation ranged in the lower quarter of the visual analogue scale.

CONCLUSIONS

In this pilot study, patients diagnosed with allergy presented a significant difference in salivary flow rate compared to healthy controls. Unlike the effect of loratadine, fexofenadine-treated patients showed significantly lower salivary flow rates compared to healthy individuals. In all cases the intensity of dry mouth was low.

Formalin injection into knee joints of rats: pharmacologic characterization of a deep somatic nociceptive model

Formalin (0.25, 0.5, 3, and 5%) injected into the knee joint of rats induced a dose-dependent nociception that was featured by 2 phases of intense guarding behavior of the affected limb, interposed by a period of quasinormal gait (quiescent phase). The guarding behavior during a period of forced gait was measured by the total time the paw of the affected limb was not in contact with the surface of a revolving cylinder (paw elevation time [PET]). Pretreatment with morphine (4 mg/kg, subcutaneously) reduced PET in both nocifensive phases, and naloxone (1 mg/kg, subcutaneously) antagonized morphine's effect. The cyclooxygenase inhibitor diclofenac (5 mg/kg, intraperitoneal) reduced only the second phase of nocifensive responses. A low dose of the benzodiazepine midazolam (0.25 mg/kg, intraperitoneal) significantly reduced only the second phase of response, but a higher dose (1 mg/kg, intraperitoneal) had no effect. A subconvulsant, anxiogenic dose of pentylenetetrazol (30 mg/kg, intraperitoneal) also did not affect the PET increase induced by formalin. The antihistamine meclizine (2.5 mg/kg, intraperitoneal) caused an increase of the response in the second phase, but a higher dose (7.5 mg/kg, intraperitoneal) caused inhibition. The peripheral antihistamine loratadine (5 and 10 mg/kg, intraperitoneal) also caused an increase of the second phase. Neither antihistamine altered the first phase of PET. These results reproduced previous findings with classical analgesics in formalin-induced nociception. However, the pronociceptive effect of antihistamines, and the antinociceptive effect of midazolam observed here suggest that formalin-induced incapacitation introduces new characterists of nociceptive system that may complement the study of analgesics.

PERSPECTIVES

Anxiety is thought to influence pain experience in an opposing manner depending on nociception originates in cutaneous or deep somatic/visceral tissues. The present formalin-induced nociceptive test may help to predict more reliably the pain-killing effect of new pharmacologic strategies, with classical or nonclassical mechanisms, for the treatment of clinically relevant pains, which are generally originated in deep structures.

A structure–activity relationship study of compounds with antihistamine activity

A structure-activity relationship (SAR) analysis of H(1)-, H(2)- and H(3)-antihistamine activity was carried out and chromatographic data of 2-[2-(phenylamino)thiazol-4-yl]ethanamine, 2-(2-benzyl-4-thiazolyl)ethanamine, 2-(2-benzhydrylthiazol4-yl)ethanamine, 2-(1-piperazinyl- and 2-(hexahydro-1H-1,4-diazepin-1-yl)benzothiazole, 2-(1-piperazinyl)benzothiazole, 2-[4-(1-alkyl)piperidinyl]benzothiazole, 2-(N,N',N'-dimethylalkyl-1,2-ethanediamino)benzothiazole, 2[1-(4-aminopiperidinyl)]benzothiazole, 2-[2-phenyl-4-thiazolyl]ethanamine derivatives and selected H(1)- and H(2)-antihistamine drugs were obtained. NP TLC and RP2 TLC plates (silica gel NP 60F(254) and silica gel RP2 60F(254) silanized precoated), impregnated with a solution of aspartic acid (L-Asp) and a solution of an analogue of aspartic acid (propionic acid), were used in two developing solvents as H(1)-, H(2)- and H(3)-antihistaminic interaction models. The lipophilicity data of the examined compounds were obtained and used in the SAR assay. Biochromatographic tests using TLC plates impregnated with solutions of asparic acid or propionic acid were found to be a source of useful data for the qualitative analysis of compounds with different structures, demonstrating activity to histamine H(1)-, H(2)- and H(3)-receptors. The four presented discriminant models based on biochromatographic studies are an efficient tool in the SAR analysis for initial prediction of compound activity direction within histamine receptors.

Effect of Olopatadine and Other Histamine H1 Receptor Antagonists on the Skin Inflammation Induced by Repeated Topical Application of Oxazolone in Mice

Histamine H1 receptor antagonists have long been prescribed for atopic dermatitis as an adjuvant therapy with topical therapy by local applied steroids. Olopatadine is one of the second-generation histamine H1 receptor antagonists that are treated for allergic disorders. We investigated that the effect of olopatadine on oxazolone-induced chronic contact hypersensitivity response in BALB/c mice compared with other histamine H1 receptor antagonists loratadine, cetirizine and fexofenadine. The chronic contact hypersensitivity induced by repeated application of oxazolone was treated with olopatadine and other histamine H1 receptor antagonists at the effective doses on histamine-induced paw edema in mice. The effects of these drugs in the oxazolone-induced model were quantified by measurements of ear swelling, and levels of cytokines in the lesioned ear. Olopatadine significantly inhibited the ear swelling and the increased production of IL-4, IL-1beta, IL-6, GM-CSF and NGF in the lesioned ear. On the other hand, the other histamine H1 receptor antagonists did not significantly suppress the increase in ear thickness. Moreover, they did not affect the production of cytokines in the lesioned ear. These results indicate that olopatadine appears to exert additional biological effects besides its blockade of the histamine H1 receptor.

Evaluation of diphenhydramine as a sedative for dogs

OBJECTIVE

To determine and compare levels of sedation achieved by IM administration of diphenhydramine, saline (0.9% NaCl) solution, and acepromazine in dogs.

DESIGN

Prospective randomized study.

ANIMALS

56 dogs.

PROCEDURE

Dogs were randomly assigned to receive diphenhydramine at 2, 4, or 8 mg/kg (0.9, 1.8, or 3.6 mg/lb, respectively) i.m.; acepromazine at 0.1 mg/kg (0.05 mg/lb) i.m.; or saline solution at 0.05 mL/kg (0.02 mL/lb) i.m. Sedation was assessed by use of a 6-category descriptive system based on observation and interaction.

RESULTS

Dogs in the acepromazine group had significantly higher sedation scores than did dogs in the saline solution or diphenhydramine groups at 30 minutes. Dogs in the diphenhydramine groups did not have significantly different sedation scores from dogs in the saline solution group at any time point.

CONCLUSIONS AND CLINICAL RELEVANCE

Diphenhydramine did not cause clinically appreciable sedation in healthy dogs. Diphenhydramine is not suitable as a sole sedative prior to general anesthesia in dogs.

Desloratadine: A new, nonsedating, oral antihistamine

Desloratadine is a new, selective, H(1)-receptor antagonist that also has anti-inflammatory activity. In vitro studies have shown that desloratadine inhibits the release or generation of multiple inflammatory mediators, including IL-4, IL-6, IL-8, IL-13, PGD(2), leukotriene C(4), tryptase, histamine, and the TNF-alpha-induced chemokine RANTES. Desloratadine also inhibits the induction of cell adhesion molecules, plateletactivating factor-induced eosinophil chemotaxis, TNF-alpha-induced eosinophil adhesion, and spontaneous and phorbol myristate acetate-induced superoxide generation in vitro. In animals desloratadine had no effect on the central nervous, cardiovascular, renal, or gastrointestinal systems. Desloratadine is rapidly absorbed, has dose-proportional pharmacokinetics, and has a half-life of 27 hours. The absorption of desloratadine is not affected by food, and the metabolism and elimination are not significantly affected by the subject's age, race, or sex. There are no clinically relevant interactions between desloratadine and erythromycin, ketoconazole, or grapefruit juice. Desloratadine is not a significant substrate of the P-glycoprotein transport system. Once daily administration of desloratadine rapidly reduces the nasal and nonnasal symptoms of seasonal allergic rhinitis, including congestion. In patients with seasonal allergic rhinitis and concomitant asthma, desloratadine treatment was also associated with significant reductions in total asthma symptom score and use of inhaled beta(2)-agonists. Use of desloratadine in patients with chronic idiopathic urticaria was associated with significant reductions in pruritus, number of hives, size of the largest hive, and interference with sleep and daily activities. Clinical experience in over 2300 patients has shown that the adverse event profile of desloratadine is similar to that of placebo; desloratadine has no clinically relevant effects on electrocardiographic parameters, does not impair wakefulness or psychomotor performance, and does not exacerbate the psychomotor impairment associated with alcohol use.

Mechanism responsible for epileptogenic activity by first-generation H1-antagonists in rats

In the present study, we have demonstrated that multiple first-generation H1-antagonists caused behavioral and EEG seizures in rats. The epileptogenic property of pyrilamine was more potent than either chlorpheniramine or diphenhydramine. In contrast, the second-generation H1-antagonists, loratadine and ebastine did not induce detectable epileptogenic activity. Intraperitoneal injection of histidine inhibited the EEG seizures induced by pyrilamine, diphenhydramine or chlorpheniramine; however no antagonism was observed with physostigmine. These results clearly suggest that the epileptogenic activity of first-generation H1-antagonists is dependent upon a centrally acting histaminergic mechanism.

Histamine H1 receptor ligands: part II. Synthesis and in vitro pharmacology of 2-[2-(phenylamino)thiazol-4-yl]ethanamine and 2-(2-benzhydrylthiazol-4-yl)ethanamine derivatives

New 2-[2-(phenylamino)thiazol-4-yl]ethanamine and 2-(2-benzhydrylthiazol-4-yl)ethanamine derivatives were prepared and tested in vitro as H1 receptor antagonists. The compounds with 2-phenylamino substitution with meta-halide substituents at the phenyl ring, showed weak H1-antagonistic activity (pA2: 4.62-5.04) and this activity was completely lost in the case of meta-methyl substituent (pA2 < 4). When the phenylamino group was replaced by benzhydryl groups of classic antihistamines, the resulting compounds exhibited slightly improved H1-antagonistic activity (at the meta-position pA2: 6.38-6.15; at the para-position pA2: 6.04-5.87).

Loratadine versus cetirizine: assessment of somnolence and motivation during the workday

OBJECTIVE

This parallel-group, double-blind study compared the somnolence and motivation profiles of 2 second-generation antihistamines, loratadine and cetirizine, in patients with allergic rhinitis.

BACKGROUND

Second-generation antihistamines were developed to provide symptomatic relief from allergic disorders without the unwanted side effects of first-generation antihistamines, including somnolence. Recent research has indicated that not all second-generation antihistamines are comparable with respect to somnolence and other cognitive processes.

METHODS

Patients aged > or = 12 years and actively exhibiting symptoms of allergic rhinitis were randomized to 2 treatment groups to receive 10 mg loratadine or 10 mg cetirizine daily at 8:00 AM for 1 week. After patients took the medication, their somnolence and degree of motivation to perform activities were recorded in an electronic diary using a visual analog scale 4 times during the workday (8:00 AM, 10:00 AM, noon, and 3:00 PM).

RESULTS

Sixty patients (31 men, 29 women) were randomized to treatment. Somnolence scores were similar for both groups at baseline and at the time of dosing (8:00 AM). However, there was a statistically significant difference in somnolence scores between the loratadine and cetirizine groups at 10:00 AM (P = 0.008), noon (P = 0.001), and 3:00 PM (P < 0.001), with the cetirizine group showing a greater degree of somnolence. The scores on motivation to perform activities were similar for both groups at the baseline and 8:00-AM measurements. In parallel with the somnolence scores, there were statistically significant differences in motivation scores between the loratadine and cetirizine groups at 10:00 AM (P = 0.014), noon (P = 0.001), and 3:00 PM (P < 0.001), indicating that patients taking loratadine were relatively more motivated during the workday.

CONCLUSION

The results of this study demonstrate that in patients aged > or = 12 years who had allergic rhinitis, cetirizine use promoted somnolence and decreased motivation to perform activities during the workday compared with loratadine.

Comparison of the response to histamine challenge of the nose and the maxillary sinus: effect of loratadine

To study the response of the maxillary sinus to histamine provocation, we performed a double-blind, randomized, crossover trial during which nonallergic subjects without symptoms of rhinitis (n = 25) received either 10 mg loratadine or placebo once daily for a week and then underwent nasal challenge with histamine (3, 10, and 30 mg/ml) followed, 24 h later, by a maxillary sinus challenge while still receiving the medication. Nasal challenge with histamine led to significant increases in vascular permeability, reflex nasal secretions, sneezing, and other nasal symptoms. Sinus challenge resulted in significant increases in vascular permeability within the sinus cavity (P < 0.01) and some nasal symptoms but no significant change in reflex nasal secretions. The response of the sinus mucosa to histamine was lower in magnitude than that of the nose. Treatment with loratadine resulted in a significant inhibition of the histamine-induced changes in both nasal and sinus cavities. Our data suggest the lack of a sinonasal reflex response to histamine provocation of the maxillary sinus of nonallergic individuals.

In vivo and ex vivo inhibitory effects of loratadine on histamine release in patients with allergic rhinitis

BACKGROUND

The aim of this study was to evaluate the in vivo and ex vivo effects of the H1-antagonist loratadine on histamine release.

METHODS

The study was designed as a double-blind, crossover trial. Ten patients with allergic rhinitis due to Dermatophagoides pteronyssinus were treated with loratadine (10 mg daily p.o.) and with placebo for 1 week, with a 2-week interval between the two treatments. Nasal lavages with saline solution were done before and after challenge with the relevant allergen at the end of treatments with loratadine and placebo. Venous blood was taken after treatments, and basophil histamine release induced by anti-IgE (10 microg/ml), N-formyl-methionyl-leucyl-phenylalanine (fMLP, 1 microM), and Ca2+ ionophore A23187 (1 microM) was evaluated by an automated fluorometric method.

RESULTS

Treatment with loratadine attenuated early antigen-induced nasal obstruction, rhinorrhea, and itching. Nasal symptoms were accompanied by a significant histamine release in the nasal lavages collected 5 min after stimulation when the patients received placebo (median 4 ng/ml, range 1-28; P < 0.05). After treatment with loratadine, histamine release in the 5-min postchallenge lavages was almost abrogated (median 0.5 ng/ml, range 0-3; P < 0.01 vs placebo). Median anti-IgE-induced histamine release from basophils was 41.9% (range 27.8-79.2) after placebo and 30.0% (range 1.7-73.3, P < 0.05) after loratadine. Active treatment exerted an inhibitory effect also on basophil histamine release induced by fMLP and Ca2+ ionophore A23187.

CONCLUSIONS

Treatment for 1 week with loratadine reduces allergen-induced nasal symptoms and inhibits in vivo and ex vivo histamine release in patients with allergic rhinitis.

Influence of food on the oral bioavailability of loratadine and pseudoephedrine from extended-release tablets in healthy volunteers

The effect of a high-fat breakfast on the bioavailability of the components of an extended-release tablet containing 10 mg loratadine in the immediate-release coating and 240 mg pseudoephedrine sulfate in the extended-release core was studied in 24 healthy male volunteers in a single-dose, two-way crossover study. The drug was administered after a 10-hour overnight fast or within 5 minutes of consuming a standardized high-fat breakfast. Serial blood samples were collected over a 48-hour period, and plasma was analyzed for loratadine and its active metabolite descarboethoxyloratadine (DCL), and pseudoephedrine. For pseudoephedrine, maximum concentration (Cmax) and area under the concentration-time curve extrapolated to infinity (AUCzero-infinity) were similar after both treatments, indicating no relevant food effect on the bioavailability of pseudoephedrine. Also, the absorption profiles of pseudoephedrine (from Wagner-Nelson analysis) were similar for the fed and fasted treatments, indicating no apparent differences in absorption. Plasma concentration-time profiles and values for Cmax and AUCzero-infinity of DCL were similar for the two treatments, indicating no relevant food effect on the pharmacokinetics of DCL. In contrast, for loratadine, administration with food resulted in a significantly increased mean Cmax (53%) and AUC from time zero to the final quantifiable sample (AUCif) (76%). However, the resultant Cmax and AUC of loratadine under fed conditions were well below those previously obtained at steady-state after multiple-dose administration of loratadine (40 mg/day) that were shown to be safe and well-tolerated in several clinical studies. The effect of food on the bioavailability and pharmacokinetic profiles of the components of a combination loratadine/pseudoephedrine extended-release tablet is not likely to be clinically significant.

The discriminative stimulus effects of tripelennamine in humans

Twenty volunteers were trained to discriminate between 75 mg tripelennamine (TP) and placebo. During the first four sessions, the drugs were identified prior to ingestion by letter code. During the next six sessions, the procedure was the same except the capsules were not identified. At the end of the 3-h session, participants indicated which capsule they believed they received using the letter codes. When correct, they received a monetary bonus. If they were correct on five sessions, they entered the third phase which had ten additional training and 12 test sessions. During tests, participants received capsules that contained other drugs, including diphenhydramine (50 and 75 mg), chlorpheniramine (4 and 6 mg), diazepam (5 and 10 mg), d-amphetamine (5 and 10 mg), as well as tripelennamine (25, 50 and 75 mg) and placebo. Thirteen participants learned the discrimination and nine entered the third phase. Except for placebo, most participants identified the test compounds as TP and labeled them as sedatives. TP produced significant changes on several subjective and physiological measures. The test compounds produced varied effects which were neither clearly dose-related nor related to the identification as TP or placebo. These results indicate that tripelennamine can function as a discriminative stimulus, but with little evidence of pharmacological specificity.

Antiallergic activity of loratadine: inhibition of leukotriene C4 release from human leucocytes

The H1 antagonist loratadine has the capacity to inhibit histamine release from human basophils. The aim of this study was to investigate whether loratadine can also inhibit leukotriene C4 (LTC4) release from human leucocytes. Basophil-enriched mononuclear cell suspensions were prepared by centrifugation of peripheral venous blood (n = 10) on discontinuous Percoll gradients. Leucocytes were stimulated with anti-IgE, N-formylmethionyl-leucyl-phenylalanine (FMLP) and Ca2+ ionophore A23187; immunoreactive (i) LTC4 release in the cell supernatant was measured by a competitive radioimmunoassay and histamine release was evaluated by an automated fluorometric technique. Loratadine, in the concentration range of 1-50 microM, exerted a dose-dependent inhibitory effect on IgE-mediated and IgE-independent histamine and iLTC4 release. The concentrations inhibiting 50% of histamine release were 30 microM (anti-IgE), 27 microM (FMLP) and 19 microM (Ca2+ ionophore A23187). The concentrations inhibiting 50% of iLTC4 release were 2.3 microM (anti-IgE). 11 microM (FMLP) and 1.7 microM (Ca2+ ionophore A23187). The inhibitory activity on iLTC4 release was optimal after preincubation for 2 h at 37 degrees C, and was no longer evident when leucocytes were stimulated 2 h after cell washing. Increased extracellular Ca2+ concentrations reduced the inhibitory activity of loratadine. These results indicate that loratadine has the capacity to inhibit the release of preformed and newly generated mediators from human basophil-enriched mononuclear cell suspensions.

Loratadine. A reappraisal of its pharmacological properties and therapeutic use in allergic disorders

Loratadine is a long-acting antihistamine agent, exhibiting partial selectivity for peripheral histamine H1-receptors. To date, loratadine has been evaluated in allergic rhinitis, urticaria and, to a limited extent, in asthma. In several large controlled comparative clinical studies, loratadine was superior to placebo, faster acting than astemizole and as effective as azatadine, cetirizine, chlorpheniramine (chlorphenamine), clemastine, hydroxyzine, mequitazine and terfenadine in patients with allergic rhinitis and chronic urticaria. The clinical effectiveness of loratadine in asthma is at present unclear. Loratadine is well tolerated. At dosages of 10 mg daily, commonly reported adverse events were somnolence, fatigue and headache. Sedation occurred less frequently with loratadine than with azatadine, cetirizine, chlorpheniramine, clemastine and mequitazine. Serious ventricular arrhythmias, as reported with some other second generation histamine H1-receptor antagonists, have not been observed with loratadine to date. Thus, loratadine, with its attributes of once daily administration, fast onset of action and essentially nonsedating properties, would appear to be an appropriate first-line agent for the treatment of allergic rhinitis or urticaria.

Antiallergic effect of ZCR-2060: antihistaminic action

The antihistaminic effect of 2-[2-[4-(diphenylmethyl)-1-piperadinyl]ethoxy] benzoic acid maleate (ZCR-2060), a newly synthesized antiallergic agent, was investigated in both in vitro and in vivo studies. ZCR-2060 clearly antagonized histamine-induced contraction of isolated guinea pig ileum and trachea. In contrast, carbachol-, BaCl2- and 5-hydroxytryptamine-induced contractions of isolated guinea pig ileum were slightly inhibited by higher concentrations of ZCR-2060. 3H-Mepyramine specific binding to membranes from guinea pig lung and brain were markedly inhibited by ZCR-2060 in a concentration-dependent fashion. In the in vitro studies, the antihistaminic effect of ZCR-2060 was greater than those of cetirizine and terfenadine, but was less than that of ketotifen. In the in vivo studies, ZCR-2060 significantly inhibited the histamine-induced cutaneous reaction in rats, when administered orally 1 hr before the histamine injection. Moreover, ZCR-2060 has a long-lasting antihistaminic effect. In the in vivo studies, the antihistaminic effect of ZCR-2060 was found to be greater than that of cetirizine and terfenadine, and it was the same as that of ketotifen. Thiopental-induced sleep and spontaneous ambulatory activity in mice, however, were unaffected by ZCR-2060 at higher doses. These results indicate that ZCR-2060 has a potent, selective and long acting histamine H1-receptor antagonistic action without causing any unwanted CNS side effect.

Sensitive gas-liquid chromatographic method for the determination of loratadine and its major active metabolite, descarboethoxyloratadine, in human plasma using a nitrogen-phosphorus detector

A sensitive gas-liquid chromatographic (GLC) method was developed for the determination of loratadine, a long-acting tricyclic antihistamine, and its active metabolite, descarboethoxyloratadine, in human plasma. The method involved extraction with organic solvent at neutral and alkaline pH. The organic layer from the neutral pH extraction was evaporated to dryness, reconstituted and injected into the GLC system. On the other hand, to the organic layer from the alkaline pH extraction trifluoroacetic anhydride was added. Following addition of H2O, the mixture was centrifuged and the organic layer was evaporated to dryness, reconstituted and injected onto the GLC system that was equipped with a nitrogen specific detector and a fused-silica capillary column. The linearity for both loratadine and descarboxyloratadine were demonstrated with r > or = 0.998 at concentrations ranging from 0.1 to 30 ng/ml. The results showed that the GLC method was accurate (bias < or = 12%) and precise (coefficient of variation, C.V., < or = 12%) for loratadine and descarboethoxyloratadine. The limit of quantitation was 0.1 ng/ml for loratadine with a C.V. of 9.2% and for descarboethoxyloratadine with a C.V. of 5.3%. The GLC method described has been demonstrated to be useful for the determination of loratadine and descarboethoxyloratadine in plasma samples of pediatric volunteers following oral administration of a single dose of 10 mg of loratadine syrup.

Efficacy of an oral antihistamine, loratadine, as compared with a nasal steroid spray, beclomethasone dipropionate, in seasonal allergic rhinitis

The aim of the study was to compare the efficacy and side-effects of oral antihistamine and nasal glucocorticoid therapy in seasonal allergic rhinitis. In a double-blind, double-dummy, group-comparative study, 60 birch and grass pollen allergic patients were treated with either loratadine (10 mg daily) or beclomethasone dipropionate (BDP) (100 micrograms in each nostril twice daily) during a 3 weeks' study period. Grading of 4 nasal and 3 non-nasal symptoms was performed at 4 weekly visits, and patients recorded daily symptoms and possible adverse experiences in a diary. Patients treated with BDP showed significantly less nasal blockage than those receiving loratadine (P less than 0.05), but there was no difference (P greater than 0.05) in other nasal symptoms (sneezing, itching and discharge). Patients treated with loratadine showed a statistically significantly greater relief in eye symptoms as compared with BDP (P less than 0.05). The side-effects caused by the 2 treatments were few and insignificant. We conclude that loratadine and intranasal BDP were effective in the treatment of seasonal allergic rhinitis, but the spectrum of individual symptoms controlled was different for the 2 drugs.

Suppressive effect of loratadine on allergen-induced histamine release in the nose

It has been speculated whether the recently developed non-sedating antihistamines may possess other properties than merely being antagonists at the H1-receptors. To investigate this suggestion 12 patients with strictly seasonal allergic rhinitis participated in a double-blind placebo controlled randomized cross-over study outside the pollen season. At steady state levels of 10 mg loratadine, a new non-sedating antihistamine, the patients were challenged with methacholine. This was followed by a nasal challenge with increasing doses of allergen. 24 h later the patients were rechallenged nasally with the same methacholine dose as the day before. The volume of the methacholine-induced nasal secretion was measured and the response to allergen was determined by scoring technique. In returned nasal lavage fluid the levels of histamine and TAME-esterase activity were measured. It was found that loratadine significantly reduced the immediate allergic nasal symptoms compared with placebo (P less than 0.01). Loratadine also reduced the allergen-induced release of histamine into the nasal cavity after the strongest allergen dose, from 9.6 +/- 1.5 (mean +/- SEM) to 6.4 +/- 1.4 ng/ml (P less than 0.05). A similar decrease in the TAME-esterase activity after treatment with loratadine was observed. The TAME-esterase activity decreased from 11.6 *10(3) +/- 2.47 *10(3) to 5.60 *10(3) +/- 1.45 *10(3) CMP (P less than 0.05). There were no significant changes between the active and placebo treatments regarding the methacholine-induced secretory response. This was true for the initial methacholine challenge as well as the secretory response 24 h later.(ABSTRACT TRUNCATED AT 250 WORDS)

Sedation and histamine H1-receptor antagonism: studies in man with the enantiomers of chlorpheniramine and dimethindene

1. The effects of 10 mg (+)- and (-)-chlorpheniramine and 5 mg (+)- and (-)-dimethindene on daytime sleep latencies, digit symbol substitution and subjective assessments of mood and well-being were studied in 6 healthy young adult humans. Each subject also took 5 mg triprolidine hydrochloride as an active control and two placebos. 2. Daytime sleep latencies were reduced with triprolidine, (+)-chlorpheniramine and (-)-dimethindene, and subjects also reported that they felt more sleepy after (+)-chlorpheniramine and (-)-dimethindene. Performance on digit symbol substitution was impaired with (+)-chlorpheniramine. 3. Changes in measures with (-)-chlorpheniramine and (+)-dimethindene were not different from changes with placebo. 4. In the present study, changes in measures of drowsiness and performance were limited to the enantiomers with high affinity for the histamine H1-receptor. These findings strongly suggest that sedation can arise from H1-receptor antagonism alone, and provide further support for the belief that the histaminergic system is concerned with the regulation of alertness in man.

Pharmacologic therapy for urticaria

Treatment of chronic urticaria presents a challenge to both practitioner and patient. Traditional H1 antagonists with good efficacy but substantial side effects are being supplanted in many cases by nonsedating H1 antagonists such as terfenadine and astemizole. Antidepressant medications and combinations of H1 and H2 antagonists offer improved results for selected patients. Further development and investigation of mast cell stabilizers and inhibitors of urticaria mediators other than histamine hold promise. A better understanding of the underlying pathogenesis remains the greatest hope of formulating rational and effective therapy.

Pharmacology of non-sedating H1 antihistamines

A review of the preclinical pharmacology of non-sedating H1 antihistamines includes comparative data on potency, duration of action, side effect liability, especially CNS depressant and anticholinergic activity and new approaches that may further enhance the efficacy of these newer compounds. Data discussed mainly involve studies in which multiple comparative agents were used and usually include astemizole, cetirizine, loratadine and terfenadine. New research approaches include the combination of PAF inhibition with antihistamine activity and the inhibitory effects these compounds may have on cellular influx in allergic diseases.

The in vivo and in vitro activity of AHR-13268D, a new antiallergic/antihistaminic agent

AHR-13268D (4-[3-[4-[Bis(4-fluorophenyl)hydroxymethyl]-1- piperidinyl]propoxy]benzoic acid, sodium salt) is a potent, long-acting water soluble, antiallergic and antihistaminic agent. AHR-13268D protects sensitive guinea pigs from collapse induced by aerosolized antigen; 1, 5, and 24 h ED50s in the test were 0.27, 0.25, 0.93 mg/kg, PO, respectively. AHR-13268D was also active when given as an aerosol, the 1 h ED50 = 0.29%. In the rat passivefoot anaphylaxis test. AHR-13268D was slightly more active (1.55 times) than AHR-5333B when given orally 1 h prior to challenge and equipotent to cromolyn when given intravenously immediately prior to challenge. AHR-13268D displayed potent, long-acting antihistaminic activity in naive guinea pigs; the 1, 5, and 24 h oral ED50s being in the range of 0.3 mg/kg. AHR-13268D (10 to 20 mg/kg, PO) attenuated the skin responses to ascaris antigen in sensitive dogs and did not alter the EEG pattern or sleep/wake patterns of cats at doses in vast excess of its antihistaminic activity. In vitro, AHR-13268D was a potent inhibitor of histamine release from rat peritoneal mast cells (IC50 = 0.51 nM) and was as potent as the reference 5-LO inhibitor phenidone in inhibiting antigen-induced contractions of guinea pig ileum in the presence of pyrilamine, atropine, and imidazole (IC50 approximately 300 microM). AHR-13268B was bioavailable (approximately 88%) from capsules or from oral solutions.

Selective inhibition of peripheral histamine responses by loratadine and terfenadine

To determine the selectivity of the non-sedating antihistamines loratadine and terfenadine and the sedating antihistamine diphenhydramine for peripheral and central histamine H1-receptors, these compounds were examined against intravenous (i.v.) and intracerebroventricular (i.c.v.) histamine-induced bronchoconstriction in anesthetized, spontaneously breathing guinea pigs. Animals were prepared with i.c.v. or i.v. cannulas and instrumented for the measurement of airway resistance (RAW) and dynamic lung compliance (CDyN). Loratadine, terfenadine or diphenhydramine were administered orally 2 h before either i.v. or i.c.v. injection of histamine. Each antihistamine blocked the i.v. histamine bronchospasm with the order of potency loratadine (ED40 = 0.08 mg/kg) greater than terfenadine (ED40 = 0.44 mg/kg) greater than diphenhydramine (ED40 = 5 mg/kg). These drugs also blocked i.c.v. histamine-induced bronchoconstrictions, but loratadine and terfenadine were approximately 10 times less potent against i.c.v. histamine bronchoconstriction than they were against i.v. histamine. In contrast, diphenhydramine was equipotent against i.c.v. and i.v. histamine bronchoconstriction. These results demonstrate that the non-sedating antihistamines loratadine and terfenadine, unlike diphenhydramine, are more effective against peripheral than central H1-receptors, probably because of poor penetration of the blood-brain barrier.

A multicentre study of loratadine, clemastine and placebo in patients with perennial allergic rhinitis

This multicentre, double-blind, randomized parallel-group study compared 3 weeks' treatment with either loratadine (Clarityn) 10 mg once daily, or clemastine (Tavegyl) 1 mg twice daily, and placebo in outpatients with active perennial allergic rhinitis. 155 patients were evaluated for efficacy and safety. Grading of four nasal and three non-nasal symptoms, rhinoscopy signs, and therapeutic response was performed on treatment days 6, 13, and 20. Patients recorded daily symptoms and possible adverse experiences in a diary, also indicating when symptoms of active rhinitis were relieved. Loratadine and clemastine were statistically significantly superior to placebo throughout the study (P less than 0.05), based on assessment of patients' nasal and eye symptoms, patients' diary scores, rhinoscopy signs of symptoms, and onset of relief. The loratadine group showed a statistically significantly (P less than 0.05) faster onset of relief of symptoms compared with the group treated with clemastine. Concerning nasal stuffiness, loratadine was significantly (P less than 0.05) superior to clemastine after 1 week's treatment. Reports of adverse reactions showed that significantly (P less than 0.05) more patients complained of sedation in the clemastine than in the loratadine group. Regarding other adverse experiences and laboratory tests, the three treatment groups were statistically comparable (P less than 0.05). The study showed that compared with placebo both loratadine and clemastine were effective in relieving nasal and eye symptoms in patients with perennial allergic rhinitis. Loratadine was safe and well tolerated and was significantly less sedative than clemastine; loratadine may therefore possess an advantage in clinical use in the treatment of perennial allergic rhinitis.

Pharmacokinetics of loratadine in patients with renal insufficiency

The disposition of loratadine, a new orally active histamine H1 receptor antagonist and its primary metabolite descarboethoxyloratadine were characterized in adult volunteers with normal renal function (group I), patients with chronic renal failure, i.e., creatinine clearance less than 30 mL/min (group II), as well as chronic hemodialysis patients (group III). The effect of hemodialysis on the disposition of loratadine and descarboethoxyloratadine was also assessed. Subjects in groups I and II were given a single oral 40 mg dose of loratadine while the patients in Group III received two single 40 mg doses of loratadine (during an interdialytic period and just prior to hemodialysis). Loratadine was rapidly absorbed and the decline of plasma concentrations after attainment of the Cmax was biexponential in all subjects. No significant differences in t1/2 beta were observed between the three groups (8.7 +/- 5.9, 7.6 +/- 6.9, 8.6 +/- 1.6 hrs: in groups I, II, and III, respectively). The apparent total body clearance and apparent volume of distribution of loratadine also did not differ significantly among the three groups. No significant differences in the Cmax or tmax of the metabolite were observed. The metabolite AUC infinity 0 however was significantly greater in group II subjects: (212.4 +/- 37.8, 469.5 +/- 95.4, 325.2 +/- 114.6 ng.hr/mL; groups I, II, and III, respectively). No significant relationship was observed between the terminal elimination half-life of loratadine or descarboethoxyloratadine and creatinine clearance. Hemodialysis augmented endogenous clearance by less than 1%. The disposition of loratadine is not significantly altered in patients with severe renal insufficiency nor is hemodialysis an effective means of removing loratadine or descarboethoxyloratadine from the body.

Treatment of hay fever with loratadine--a new non-sedating antihistamine

The efficacy and safety of loratadine, a new orally active specific H1-receptor blocking antihistamine with poor penetration into the CNS, was evaluated in a double blind comparative study. One hundred and seven hay fever patients, sensitive to birch pollen, were randomized into three parallel groups receiving loratadine 40 mg once daily, clemastine 1 mg twice daily, or placebo during the birch pollen season. Both active treatments showed reduction of symptoms in comparison with placebo, but the results were more pronounced with loratadine treatment, which significantly reduced the overall allergic condition as well as all separate allergic rhino-conjunctivitis symptoms except nasal stuffiness. Compared with placebo the sedation rate was significantly higher with clemastine treatment (P less than 0.05) but not with loratadine. Loratadine was thus concluded to be efficacious in hay fever treatment with a sedation rate not differing from placebo.