Antitussive action of antihistamines is independent of sedative and ventilation activity in the guinea pig

Medicinal Plants Combating Against Insomnia: A Green Anti-Insomnia Approach

Insomnia is a state defined as trouble with sleep; it is a chronically disabling condition and is now significantly prevalent, imposing enormous health and economic burdens both on individuals and on society. This state includes trouble in falling asleep, problems staying asleep, fragmented sleep (repeatedly awakening at night), and/or awakening before time in the morning. This difficulty in sleeping causes feeling exhausted during the day and trouble with daytime activities including driving, family responsibilities, and completion of valued daily routines. Different types of synthetic sedative drugs are used to handle nervous system changes, but repeated use of sedatives caused tolerance in the human body. After a while, people had to take a heavy dose of sedative to make them feel sleepy, which imposes extra toxic effects on vital organs of the body. Medicinal plants are gaining more and more attention as sedative agents because herbs contained different types of natural bioactive metabolites with not well reported side effects. In addition, medicinal plants have economic, high efficacy and are easy available. So in current review plants possessing sedative activities have been compiled with their constituents responsible to manage insomnia. Review of the literature indicated that medicinal plants from various systems of medicine have been reported to possess sedative activity. This review suggests that medicinal plants are efficacious for insomnia; further laboratory and clinical studies are required.

Regulation of cough by neuronal Na(+)-K(+) ATPases

The Na(+)-K(+) ATPases play an essential role in establishing the sodium gradients in excitable cells. Multiple isoforms of the sodium pumps have been identified, with tissue and cell specific expression patterns. Because the vagal afferent nerves regulating cough must be activated at sustained high frequencies of action potential patterning to achieve cough initiation thresholds, it is a certainty that sodium pump function is essential to maintaining cough reflex sensitivities in health and in disease. The mechanisms by which Na(+)-K(+) ATPases regulate bronchopulmonary vagal afferent nerve excitability are reviewed as are potential therapeutic strategies targeting the sodium pumps in cough.

Effect of memantine on cough reflex sensitivity: translational studies in guinea pigs and humans

Cough is the most common complaint for which outpatients in the United States seek medical attention, and yet available therapeutic options for cough lack proven efficacy and are further limited by safety and abuse liabilities. Thus, safe and effective cough suppressants are needed. Recent preclinical studies described the antitussive effects of memantine, an N-methyl-d-aspartate receptor channel blocker used in the treatment of Alzheimer's disease. The goals of the present study were to compare the antitussive effects of memantine, dextromethorphan, and codeine in guinea pigs; to relate the dose-dependent actions of memantine in these studies to peak plasma concentrations achieved following oral administration; and to provide the first ever evaluation of the antitussive effect of memantine in humans. In guinea pigs, memantine and codeine were comparable in efficacy and potency but both were superior to dextromethorphan in the citric acid cough challenge model. The pharmacokinetic analyses suggest that memantine was active in guinea pigs at micromolar plasma concentrations. Subsequently, 14 healthy volunteers as well as 14 otherwise healthy adults with acute viral upper respiratory tract infection (URI) underwent capsaicin cough challenges 6 hours after ingestion of 20 mg memantine and matched placebo in a randomized, double-blind, crossover fashion. In healthy volunteers, memantine significantly inhibited cough reflex sensitivity (P = 0.034). In subjects with URI, responsiveness to capsaicin was markedly increased, and in these patients, the inhibition of cough reflex sensitivity by memantine relative to placebo did not reach statistical significance (P = 0.088). These data support further research to investigate the potential of memantine as a clinically useful antitussive.

Antitussive drugs--past, present, and future

Cough remains a serious unmet clinical problem, both as a symptom of a range of other conditions such as asthma, chronic obstructive pulmonary disease, gastroesophageal reflux, and as a problem in its own right in patients with chronic cough of unknown origin. This article reviews our current understanding of the pathogenesis of cough and the hypertussive state characterizing a number of diseases as well as reviewing the evidence for the different classes of antitussive drug currently in clinical use. For completeness, the review also discusses a number of major drug classes often clinically used to treat cough but that are not generally classified as antitussive drugs. We also reviewed a number of drug classes in various stages of development as antitussive drugs. Perhaps surprising for drugs used to treat such a common symptom, there is a paucity of well-controlled clinical studies documenting evidence for the use of many of the drug classes in use today, particularly those available over the counter. Nonetheless, there has been a considerable increase in our understanding of the cough reflex over the last decade that has led to a number of promising new targets for antitussive drugs being identified and thus giving some hope of new drugs being available in the not too distant future for the treatment of this often debilitating symptom.

The conventional antihistamine drug cyproheptadine lacks QT-interval-prolonging action in halothane-anesthetized guinea pigs: comparison with hydroxyzine

Antihistamines are known to belong to the chemical class that may induce long QT syndrome. Among them, cyproheptadine has been shown to exert multifaceted actions on the ventricular repolarization phase; namely, shortening of the action potential duration at supra-therapeutic concentrations of 2 - 8 μM and prolongation of the QT interval at ≥ 10 μM. Since information is limited regarding the in vivo electrophysiological effects of cyproheptadine, we assessed it using the halothane-anesthetized guinea-pig model, which was compared with effects of another antihistamine drug, hydroxyzine. Sub-therapeutic to therapeutic doses of hydroxyzine at 1 and 10 mg/kg, i.v. prolonged the QT interval and duration of monophasic action potential, whereas therapeutic to supra-therapeutic doses of cyproheptadine at 0.1 and 1 mg/kg, i.v. hardly affected the indices of ventricular repolarization. These results suggest that cyproheptadine may be categorized into antihistamines with little effect on the ventricular repolarization.

Management of patients with chronic cough using a clinical protocol: a prospective observational study

Background and aims

Chronic cough is a common symptom the aetiology of which can be challenging to diagnose. Diagnostic protocols for chronic cough have required the use of specialist investigations which are not always easily available. We wanted to determine whether patients with chronic cough can be successfully managed using a clinical algorithm.

Methods

112 consecutive patients with chronic cough were prospectively recruited into this study. They were assessed by history, physical examination, chest radiograph, spirometry and reversibility to nebulised salbutamol. A clinical diagnosis was made and the patient had an 8-week trial of appropriate therapy. Further therapeutic trials were carried out depending on response to treatment and the possible differential diagnoses. Investigations were carried out in cases of failed clinical trials and to exclude specific pathology. The “clinical arm” comprised patients managed on the basis of clinical assessment and without any investigations. The “investigative arm” comprised those who needed further investigations.

Results

81 (72%) were managed in the clinical arm. Of these 74 (66%) were discharged following response to therapy. 31 (28%) patients were converted to the investigative arm after failure of diagnosis in the clinical protocol. The commonest causes of cough were gastroesophageal reflux, asthma and chronic rhinitis. 51 (45.5%) patients responded to therapy based on diagnosis at initial assessment while a further 23 (20.5%) patients responded to sequential clinical trials for the commonest causes of cough. Cough severity score improved by a mean of 3.6 points on a numeric response score (from 0–10, p < 0.0001).

Conclusion

It is possible to manage a majority of chronic cough patients successfully using a protocol based on presenting symptoms and therapeutic trials for the common causes of cough.

Controversies in the evaluation and management of chronic cough

Chronic cough that cannot be explained after basic evaluation is a common reason for patients to be referred to respiratory outpatient clinics. Asthma, gastroesophageal reflux, and upper airway disorders frequently coexist with chronic cough. There is some controversy as to whether these conditions are causes or aggravants of cough. Heightened cough reflex sensitivity is an important feature in most patients. There is good evidence that it is reversible when associated with upper respiratory tract infection, angiotensin-converting enzyme inhibitor medications, and chronic cough associated with eosinophilic airway inflammation. In many patients, heightened cough reflex sensitivity is persistent and their cough is unexplained. There are few therapeutic options for patients with unexplained chronic cough. There is a pressing need to understand the genetic, molecular, and physiological basis of unexplained chronic cough and to develop novel antitussive drugs that down-regulate cough reflex sensitivity.

Pharmacological profile of the NOP agonist and cough suppressing agent SCH 486757 (8-[Bis(2-Chlorophenyl)Methyl]-3-(2-Pyrimidinyl)-8-Azabicyclo[3.2.1]Octan-3-Ol) in preclinical models

We describe the pharmacological and pharmacokinetic profiles of SCH 486757, a nociceptin/orphanin FQ peptide (NOP) receptor agonist that has recently entered human clinical trials for cough. SCH 486757 selectively binds human NOP receptor (K(i)=4.6+/-0.61nM) over classical opioid receptors. In a guinea pig capsaicin cough model, SCH 486757 (0.01-1mg/kg) suppressed cough at 2, 4, and 6h post oral administration with a maximum efficacy occurring at 4h equivalent to codeine, hydrocodone, dextromethorphan and baclofen. The antitussive effects of SCH 486757 (3.0mg/kg, p.o.) was blocked by the NOP receptor antagonist J113397 (12mg/kg, i.p.) but not by naltrexone (10mg/kg, p.o.). SCH 486757 does not produce tolerance to its antitussive activity after a 5-day BID dosing regimen. After acute and chronic dosing paradigms, SCH 486757 (1mg/kg) inhibited capsaicin-evoked coughing by 46+/-9% and 40+/-11%, respectively. In a feline mechanically-evoked cough model, SCH 486757 produces a maximum inhibition of cough and expiratory abdominal electromyogram amplitude of 59 and 61%, respectively. SCH 486757 did not significantly affect inspiratory electromyogram amplitude. We examined the abuse potential of SCH 486757 (10mg/kg, p.o.) in a rat conditioned place preference procedure which is sensitive to classical drugs of abuse, such as amphetamine and morphine. SCH 486757 was without effect in this model. Finally, SCH 486757 displays a good oral pharmacokinetic profile in the guinea pig, rat and dog. We conclude that SCH 486757 has a favorable antitussive profile in preclinical animal models.

Management of chronic cough

Cough that remains unexplained after basic clinical assessment is a common reason for referral to secondary care. Much of the evidence about management of isolated chronic cough is derived from case series; this evidence suggests that isolated chronic cough is usually due to asthma, gastro-oesophageal reflux disease, and upper airway conditions, and that it can be cured in most people by treatment of these conditions. However, there is increasing recognition that satisfactory control of chronic cough is not achieved in a substantial number of patients seen in secondary care. Moreover, there is a concern that perpetuation of the belief that chronic cough is solely due to the effects of comorbid conditions is inhibiting research into the pathophysiology of an abnormally heightened cough reflex, and jeopardising development of improved treatments. We advocate a change in emphasis, which makes a clear distinction between cough due to corticosteroid-responsive eosinophilic airway diseases and corticosteroid-resistant non-eosinophilic cough. We recommend that some factors with weak evidence of an association with cough are best viewed as potential aggravating factors of an intrinsic abnormality of the cough reflex, rather than the cause. We call for more research into the basic mechanisms and pharmacological control of an abnormally heightened cough reflex, and recommend ways to assess the effects of potentially antitussive treatments.

Older-generation antihistamines and cough due to upper airway cough syndrome (UACS): efficacy and mechanism

Older-generation H1 antihistamines are recommended in empiric protocols for the treatment of cough due to upper airway cough syndrome (UACS). Data from double-blind placebo-controlled trials that support the use of older-generation antihistamines in UACS are limited to a single study of cough due to the common cold. However, several empiric trials strongly support efficacy of older-generation antihistamines in patients with chronic cough. Data from a variety of studies support the concept that newer-generation H1 antihistamines are not useful in the treatment of cough due to UACS. The mechanism of action of older-generation H1 antihistamines has been proposed to be anticholinergic activity, but the rank order potency of these drugs as muscarinic receptor antagonists is not consistent with this hypothesis. Actions of these drugs on histamine H1 and/or nonhistaminergic receptors in the central nervous system remain a possible explanation for their effects on cough due to UACS. The effects of older H1 antihistamines may also be molecule specific, rather than attributable to the entire class of compounds. Additional studies should be performed to document the activity of these drugs in double-blind placebo-controlled trials.

Sulfur-dioxide exposure increases TRPV1-mediated responses in nodose ganglia cells and augments cough in guinea pigs

The objective of the present experiments was to study the effects of pulmonary inflammation induced by subacute Sulfur-dioxide (SO(2)) exposure on capsaicin-induced responses in isolated primary vagal sensory neurons and cough. Additionally, we examined the effects of SO(2) exposure on respiratory function and lung histology. All experiments were conducted 24 h after 4 days of subacute SO(2) (1000 ppm, 3 h/day for 4 days) exposure. In in vitro experiments, intracellular Ca(2+) concentrations were measured in single nodose ganglia cells isolated from SO(2) treated and control guinea pigs, using a fluorescence-based methodology. In nodose ganglia cells from SO(2)-exposed animals, intracellular Ca(2+) responses evoked by capsaicin (1 x 10(-7) and 1 x 10(-6) M) were significantly augmented (87% and 59%, respectively) compared to nodose ganglia from control animals. In vivo experiments, cough responses induced by a submaximal dose of aerosolized capsaicin (30 microM) were increased approximately 50% in SO(2) exposed animals compared to control animals. The enhanced cough response produced by SO(2) was inhibited by the corticosteroid, dexamethasone (10 mg/kg, p.o. b.i.d for 4 days and 10 mg/kg, p.o. once on day 5). In separate experiments, guinea pigs exposed to SO(2) displayed a decrease in respiratory frequency and minute ventilation and an increase in enhanced pause (PenH), a surrogate measure for pulmonary obstruction. Associated with the SO(2)-induced increase in cough and changes in respiratory parameters was an increase in BAL neutrophils. BAL neutrophil counts were 5+/-4 and 691+/-141 cells x 10(3)/ml for air and SO(2)-exposed animals, respectively. The neutrophillic inflammation induced by SO(2) was attenuated by dexamethasone treatment. Finally, staining for collagen, smooth muscle and goblet cells showed inflammation, remodeling and goblet cell metaphasia in the SO(2)-exposed animals. Our results demonstrate that SO(2) exposure enhances TRPV1 receptor function at the level of the nodose ganglia. This effect occurs in parallel with an increase sensitivity of the cough response to capsaicin.

Current and future centrally acting antitussives

The purpose of this review is to highlight some important issues regarding current centrally acting antitussive drugs as well as discuss the implications of these matters on the development of future cough suppressants. Drugs that act in the central nervous system to inhibit cough are termed centrally acting and this designation is based exclusively on evidence obtained from animal models. This classification can include drugs that act both at peripheral and central sites following systemic administration. These drugs are intended to reduce the frequency and/or intensity of coughing resulting from disorders of any etiology. There are a number of central cough suppressants identified by their efficacy in animal models and the most prominent of these are codeine and dextromethorphan. Although the exact neural elements on which these drugs act are currently unknown, they are thought to inhibit a functionally identified component of the central system for cough known as the gating mechanism. The efficacy of codeine and dextromethorphan in humans has recently been questioned. These drugs are less effective on cough induced by upper airway disorders than in pathological conditions involving the lower airways in humans. The reasons for this difference in antitussive sensitivity are not clear. We propose that sensory afferents from different regions of the airways actuate coughing in humans by antitussive sensitive and insensitive control elements in the central nervous system. This hypothesis is consistent with results from an animal model in which laryngeal and tracheobronchial cough had different sensitivities to codeine. Other factors that may be very important in the action of central antitussive drugs in humans include the role of sensations produced by a tussigenic stimulus as well as plasticity of central pathways in response to airway inflammation. Resolution of these issues in the human will be a challenging process, but one which will lay the foundation for the development of more effective cough suppressants.

Second-Generation Antihistamines

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

Antitussive profile of the NOP agonist Ro-64-6198 in the guinea pig

We have previously shown that N/OFQ, the endogenous peptide ligand for the 'opioid-like' NOP receptor, inhibits cough in guinea pigs and cats. In the present study we sought to continue our characterization of the cough-suppressant effects of NOP stimulation by profiling the pulmonary and antitussive effects of a novel non-peptide NOP agonist, Ro-64-6198, in guinea pigs. In receptor-binding assays, we confirmed that Ro-64-6198 selectively binds to NOP receptors over other opioid receptors. The Ki values for Ro-64-6198 at NOP, MOP, KOP and DOP receptors was 0.3, 36, 214 and 3,787 nmol/l, respectively. In GTPgammaS-binding assays, Ro-64-6198 displayed >900-fold functional selectivity at NOP relative to MOP receptors. We evaluated the effects of Ro-64-6198 (3 and 10 micromol/l) in isolated guinea pig nodose ganglia cells on the increases in intracellular Ca2+ concentration evoked by capsaicin stimulation (1 x 10(-8)-1 x 10(-6) mol/l). Similar to previously reported data with N/OFQ, Ro-64-6198 (3 and 10 micromol/l) significantly attenuated Ca2+ responses in nodose ganglia cells produced by exposure to capsaicin. The effect of Ro-64-6198 (3 micromol/l) on capsaicin-induced intracellular Ca2+ responses was blocked by the NOP antagonist, J113397 (3 micromol/l). In guinea pig in vivo studies, aerosolized capsaicin (10-300 micromol/l) produced a dose-dependent increase in cough number. Ro-64-6198 given i.p. significantly inhibited cough due to capsaicin (300 micromol/l) exposure. In a duration study we found that the maximum antitussive effect (42 +/- 8% inhibition) of Ro-64-6198 (3 mg/kg) was observed at 1 h after i.p. administration. Also at 1 h after administration, Ro-64-6198 (0.003-3.0 mg/kg, i.p.) produced a dose-dependent inhibition of cough. The antitussive effect of Ro-64-6198 (3 mg/kg, i.p.) was blocked by J113397 (12 mg/kg, i.p.) but not by the classical opioid antagonist naltrexone (10 mg/kg, i.p.). Although the antitussive action of Ro-64-6198 may be mediated by a central and/or a peripheral site of action, we hypothesize that selective oral NOP agonists that do not penetrate the blood-brain barrier may provide a novel approach for the treatment of cough. Moreover, because these drugs do not interact at MOP receptors, they may be devoid of codeine-like side effects such as respiratory depression, sedation, constipation or proclivities for addictive liabilities.

Effect of the second-generation antihistamine, fexofenadine, on cough reflex sensitivity and pulmonary function

AIMS

Current guidelines recommend the use of first-generation antihistamines for the treatment of cough due to rhinitis/postnasal drip syndrome. The antitussive activity of the second-generation antihistamine, fexofenadine, has not been investigated. Therefore, we evaluated the effect of fexofenadine on capsaicin-induced cough in healthy volunteers and in subjects with acute viral upper respiratory tract infection (URI).

METHODS

Twelve healthy volunteers and 12 subjects with URI underwent pulmonary function testing and capsaicin cough challenge on two separate days, 2 h after ingesting 180 mg fexofenadine or matched placebo. Subjects inhaled single, vital-capacity breaths of capsaicin aerosol, administered in incremental doubling concentrations, until the concentration inducing five or more coughs (C5) was determined.

RESULTS

In both subject groups, C5 was not significantly different after fexofenadine compared to placebo. In subjects with URI, pulmonary function studies were also similar. In healthy volunteers, however, FEV1 and FEF(25-75), pulmonary function parameters reflecting the degree of airway dilatation, were significantly increased after fexofenadine. Mean (95% CI) values for FEV1(L) after fexofenadine and placebo were 3.16 (2.77, 3.55) and 3.08 (2.69, 3.47), respectively (P = 0.017). Mean values for FEF(25-75)(L/s) were 3.49 (3.10, 3.88) and 3.26 (2.79, 3.72), respectively (P = 0.029).

CONCLUSIONS

Fexofenadine demonstrated no antitussive activity against capsaicin-induced cough in healthy volunteers and subjects with URI. The ineffectiveness of fexofenadine in suppressing cough probably reflects the lack of anticholinergic activity and central nervous system penetrance that is characteristic of first-generation antihistamines. The mild bronchodilation induced by fexofenadine in healthy volunteers is of unclear clinical significance and requires further investigation.

Relative efficacies of gastric proton pump inhibitors: their clinical and pharmacological basis

The present review will verify by intra-study rank orders, and their comparison between studies, that the different gastric proton pump inhibitors (PPIs) display similar dose-response relationships with similar potencies and efficacies on a milligram basis, i.e., at the same milligram doses. This is in line with their basic pharmacology which suggests that, primarily, the serum AUCs of the free pro-drugs and their chemical activation half lives at pH 1 relative to their serum elimination half lives determine the efficacies of PPIs. According to the literature, these drug characteristics are similar for all PPIs. Although PPIs have been introduced into the therapy of acute peptic ulcer disease at different daily, oral doses of 20 mg (omeprazole and rabeprazole), 30 mg (lansoprazole) and 40 mg (pantoprazole), the data suggest that the optimal dose of lansoprazole, omeprazole and pantoprazole, with respect to the acute treatment of peptic ulcers and moderate to severe gastroesophageal reflux disease (GERD), is about 30-40 mg daily. The data base of rabeprazole appears to be too small at present to make any definite statement. Lower daily doses of the PPIs of about 15-20 mg are sufficient in less severe cases of GERD and in maintenance therapy. It appears that different dose recommendations were based on different strategies to balance optimal drug dosage and safety, rather than on real differences in milligram-related efficacies.