Effect of viral upper respiratory tract infection on the urge-to-cough sensation

BACKGROUND

Recently, interest has emerged in the sensation of irritation that precedes the motor act of coughing; this phenomenon has been termed the urge-to-cough (UTC). Although one previous study has demonstrated a transient enhancement of cough reflex sensitivity during acute upper respiratory tract infection (URI), the effect of URI on UTC has not previously been investigated.

METHODS

Employing standard cough challenge methodology, we measured cough reflex sensitivity in 24 otherwise healthy adult nonsmokers during URI and again after recovery (4-8 weeks later) by determining C(2) and C(5), the concentrations of capsaicin inducing 2 or more and 5 or more coughs, respectively. In addition, we determined the capsaicin concentration at which the UTC sensation first occurred, without an associated motor cough, and termed it C(u). Furthermore, we determined the difference between concentrations of capsaicin inducing the first motor event of cough (C(1)) and C(u), and have termed it C(Δ).

RESULTS

During URI, cough reflex sensitivity as measured by C(1) (p = 0.033) and C(5) (p = 0.001), as well as the urge-to-cough threshold, C(u) (p = 0.046), were significantly enhanced compared to the post-recovery state. The degree of change in cough reflex sensitivity (C(5)) was significantly greater than that of the urge-to-cough threshold, C(u) (p = 0.044).

CONCLUSION

Our results demonstrate that the UTC sensation is transiently enhanced during URI. We also confirm the results of the lone previous study that demonstrated transient enhancement of cough reflex sensitivity during URI. The UTC threshold may represent an additional relevant end point to measure in future studies evaluating potential antitussive agents.

Acute cough: a diagnostic and therapeutic challenge

BACKGROUND

Acute cough is one of the most common complaints prompting patient visits to healthcare professionals. Despite the broad repercussions of acute cough on patient quality of life, school and work productivity, and public health resources, research on this condition is minimal, as are the available treatment options. Many patients use over-the-counter medicines, which are often ineffective for symptom relief. Some therapies may achieve antitussive activity, but at the expense of unpleasant or intolerable side effects.

UNMET NEEDS

When considering the treatments currently available for the management of acute cough, the multiple limitations of such treatments are quite apparent. Most of these treatments lack clinically proven efficacy and reliability to support their use. This reinforces the need for the generation of quality scientific data from well-performed clinical trials. Hopefully, the result will be the development of safer, more effective and more reliable therapeutic options in the management of acute cough.

COUGH ASSESSMENT AND MANAGEMENT

Acute cough can be due to a variety of causes, and it is worthwhile to consider these pathogenic factors in some detail. It is also important to be familiar with the effects that acute cough has on patients' quality of life, work productivity, and the healthcare system; proper awareness of these effects may contribute to better understanding of the social impact of cough. In reference to the available treatments for the management of acute cough, adequate knowledge of the type of over-the-counter and prescription products in the market, as well as their mode of action and advantages/disadvantages, may provide expanded pharmacotherapeutic opportunities and facilitate better clinical decisions. However, due to the drawbacks of current treatment options, ideas for future cough management and newer products need to be considered and tested.

CONCLUSION

In view of the socio-economic impact of acute cough and the limitations of available treatments, a renewed interest in the management of acute cough needs to be encouraged. The current strategies for acute cough management need to be reassessed, with a focus on developing new, reliable products and formulations with proven efficacy and safety.

WITHDRAWN: Short- and Long-term Reproducibility of Capsaicin Cough Challenge Testing

The publisher regrets that this is an accidental duplication of an article that has already been published inPulm. Pharmacol. Ther., 16 (2003) 61-65, doi:10.1016/S1094-5539(02)00149-9. The duplicate article has therefore been withdrawn.

Phase II, randomized, multicenter, double-blind, placebo-controlled trial of a polyclonal anti-Staphylococcus aureus capsular polysaccharide immune globulin in treatment of Staphylococcus aureus bacteremia

New treatment modalities are needed for the treatment of infections due to multidrug-resistant Staphylococcus aureus. S. aureus capsular polysaccharide immune globulin (Altastaph) is a polyclonal immune globulin preparation that is being developed as adjunctive therapy for persons with S. aureus infections complicated by bacteremia. In a phase II, multicenter, randomized, double-blind, placebo-controlled trial, 40 subjects with documented S. aureus bacteremia received standard therapy plus either Altastaph at 200 mg/kg of body weight in each of two infusions 24 h apart or placebo. During the 42-day observation period, antibody pharmacokinetics and safety were the primary characteristics studied. Information regarding the resolution of bacteremia and fever was also analyzed. Anti-type-5 and anti-type-8 capsular antibody levels peaked after the second infusion at 550 mug/ml and 419 mug/ml, respectively, and remained above 100 mug/ml at day 28. A total of 316 adverse events were noted in 39 of 40 subjects. Infusion-related adverse events in Altastaph recipients were infrequent and similar to those among recipients of commercial intravenously administered immunoglobulin G products. Five of 21 (23%) subjects in the Altastaph group died, whereas 2 of 18 (11%) subjects in the placebo group died (P = 0.42). Compared to the control patients, the Altastaph recipients had a shorter median time to the resolution of fever (2 days and 7 days, respectively; P = 0.09) and a shorter length of hospital stay (9 days and 14 days, respectively; P = 0.03). However, these findings are exploratory, and there were few differences in the other variables measured. High levels of opsonizing antibodies were maintained for the initial 4 weeks. Although the study was not powered to show efficacy, these preliminary findings and safety profile suggest that Altastaph may be an effective adjunct to antibiotics and warrants further investigation (ClinicalTrials.gov number NCT00063089).

Experimentally induced cough

The experimental induction of cough has become an important component of clinical cough research. Measurement of cough reflex sensitivity allows the evaluation of the effect of pharmacological and other interventions on the cough reflex, as well as the performance of epidemiological studies relevant to cough. The most commonly used tussive agents include capsaicin, citric acid and ultrasonically nebulized distilled water (fog). Methodological considerations are vital to the performance of high quality, reproducible cough challenge, which is especially important when measuring the effect of an experimental intervention on cough reflex sensitivity. For the optimal execution of clinical trials employing inhalation cough challenge, the subject population must be carefully selected, and the usefulness and potential limitations of data obtained from cough challenge studies need to be appreciated.

Changes in cough reflex sensitivity after cessation and resumption of cigarette smoking

Previous studies have shown that healthy cigarette smokers have diminished cough reflex sensitivity compared to healthy nonsmokers. We have recently demonstrated that cough reflex sensitivity is enhanced soon after smoking cessation, suggesting that diminished cough sensitivity in smokers results from chronic cigarette smoke-induced desensitization of airway cough receptors. In this study, we evaluated cough reflex sensitivity to capsaicin (C(5)) in 11 chronic smokers who had discontinued smoking for at least 2 weeks, and then resumed smoking. Two weeks after smoking cessation there was a significant enhancement of cough reflex sensitivity; mean (+/-SEM) log C(5) decreased from 1.77+/-0.18 to 1.47+/-0.14 (p=0.01). All subjects resumed smoking after 2-12 weeks of abstinence. Repeat capsaicin cough challenge was performed 14-23 days after resumption of smoking. Mean log C(5) increased compared to the last value obtained during the smoking cessation period: 1.42+/-0.15 vs. 1.77+/-0.16 (p=0.0004). Mean log C(5) after resumption of smoking returned to almost exactly the baseline value. Our findings suggest that the sensitivity of airway cough receptors is a dynamic phenomenon, promptly affected and modulated by changes in environmental conditions, such as the presence or absence of cigarette smoke.

Prevalence of Depressive Symptoms Among Patients With Chronic Cough

STUDY OBJECTIVES

Cough is the most common complaint for which patients in the United States seek medical attention. Although the significant effect of cough on quality of life has been reported, the association of chronic cough with depressive symptomatology has not previously been investigated.

DESIGN

Prospective, nonrandomized evaluation.

SETTING

Outpatient department of academic medical center.

PATIENTS

Representative sample of patients presenting to a specialty center seeking evaluation and treatment of chronic cough.

INTERVENTIONS

Participants completed the Center for Epidemiologic Studies Depression Scale (CES-D), a 20-item self-report questionnaire designed to measure depressive symptomatology and risk for clinical depression, on initial evaluation and again after 3 months. Patients also provided subjective cough scores reflecting the severity of their cough.

MEASUREMENTS AND RESULTS

Of 100 patients undergoing initial evaluation, 53% scored positive (>/= 16) on the CES-D. Mean CES-D score was 18.3 +/- 13.2 (+/- SD). Among 81 subjects followed up at 3 months, mean CES-D score fell to 7.4 +/- 10.4, and subjective cough score decreased from 10 to 4.9 +/- 3.1. There was a statistically significant improvement in both cough and depression scores after 3 months (p < 0.001). Improvement in cough score correlated significantly with improvement in depression score (p = 0.003; Spearman rho = 0.323).

CONCLUSION

Depressive symptomatology is very common in patients with chronic cough. Physicians and other caregivers must be aware of the significant risk of clinical depression in this patient population.

Effect of smoking cessation on cough reflex sensitivity

Recent studies have shown that cigarette smokers have diminished cough reflex sensitivity compared with nonsmokers. The current authors proposed a mechanism of chronic cigarette smoke-induced desensitisation of airway cough receptors. To investigate this hypothesis, cough sensitivity to inhaled capsaicin (C5) in chronic smokers was measured both while they were actively smoking and 2, 6, 12 and 24 weeks after smoking cessation. In total, 29 subjects underwent baseline capsaicin challenge while smoking and 2 weeks after smoking cessation. Mean+/-sem log C5 fell from 1.86+/-0.12 to 1.60+/-0.12, demonstrating significant enhancement of cough reflex sensitivity. Of the total, 20, 18 and 14 subjects successfully abstained from smoking for 6, 12 and 24 weeks, respectively. Mean log C5 values after 12 and 24 weeks of smoking cessation were significantly diminished from baseline. In a control group of smokers, mean log C5 did not decrease from baseline after 6, 12 and 24 weeks. Overall, the log C5 profile of the smoking cessation group showed a clear, linearly decreasing trend over time compared with the control group. Even after many years of smoking, cough sensitivity is enhanced as early as 2 weeks after smoking cessation. Given the importance of an intact cough reflex, these changes may provide clinical benefit.

Chronic cough due to asthma: ACCP evidence-based clinical practice guidelines

BACKGROUND

Asthma is among the most common causes of chronic cough in adult nonsmokers. Although cough usually accompanies dyspnea and wheezing, it may present in isolation as a precursor of typical asthmatic symptoms, or it may remain the predominant or sole symptom of asthma. The latter condition is known as cough-variant asthma (CVA).

METHODS

Data for this review were obtained from a National Library of Medicine (PubMed) search, performed in April 2004, of the English language literature from 1975 to 2004, limited to human studies, using the search terms "cough" and "asthma."

RESULTS

The diagnosis of cough not associated with typical asthmatic symptoms (ie, CVA) presents a challenge, because physical examination and spirometry findings may be entirely normal. Methacholine inhalation challenge testing can demonstrate the presence of bronchial hyperresponsiveness; however, the diagnosis of cough due to asthma is only confirmed after the resolution of cough with antiasthmatic therapy. In general, the therapeutic approach to asthmatic cough is similar to that of the typical form of asthma. Most patients will respond to inhaled bronchodilators and inhaled corticosteroids. A subgroup of patients will require the addition of leukotriene receptor antagonists and/or a short course of oral corticosteroids.

CONCLUSIONS

Asthma should be considered as a potential etiology in any patient with chronic cough, because asthma is a common condition that is commonly associated with cough. Because the subgroup of asthmatic patients with CVA presents with no other symptoms of asthma, clinical suspicion must remain high. Cough due to asthma responds to standard antiasthmatic therapy.

Potential future therapies for the management of cough: ACCP evidence-based clinical practice guidelines

BACKGROUND

When the etiology of a patient's chronic cough is established, specific antitussive therapy that is aimed at a particular cause of cough is highly effective. Nevertheless, in certain situations, therapy with cough suppressants, which previously were classified as nonspecific antitussive therapy, and which aim at suppressing the cough reflex regardless of the cause of cough, will be necessary.

METHODOLOGY

The data for this review were obtained with the aid of a National Library of Medicine (PubMed) search, which was performed in June 2004, of literature published in the English language from 1966 to 2004, using the search terms "cough," "antitussive," "pharmacotherapy," "future therapies, " and "potential therapies."

RESULTS/CONCLUSIONS

Currently available cough-suppressant therapy is severely limited by a dearth of effective agents and/or their unacceptable side effects. Several classes of pharmacologic agents are currently under investigation in an attempt to develop clinically useful cough suppressants.

Current and future peripherally-acting antitussives

Cough is among the most common complaints for which medical evaluation is sought. The clinical significance of this problem is evidenced by the enormous financial expenditure on prescription and non-prescription cough remedies worldwide. Centrally-acting antitussive agents, such as opiates, are often associated with undesirable or intolerable side effects, including sedation, nausea, and constipation. Therefore, safe and effective peripherally-acting antitussive agents are particularly desirable. Relatively few commercially-available products suppress cough through a peripheral mechanism of action. Recent research in the field of cough has resulted in the development of several new classes of compounds that may prove to be clinically useful peripherally-acting antitussives.

Angiotensin-Converting Enzyme Inhibitor-Induced Cough

BACKGROUND

A dry, persistent cough is a well-described class effect of the angiotensin-converting enzyme (ACE) inhibitor medications. The mechanism of ACE inhibitor-induced cough remains unresolved, but likely involves the protussive mediators bradykinin and substance P, agents that are degraded by ACE and therefore accumulate in the upper respiratory tract or lung when the enzyme is inhibited, and prostaglandins, the production of which may be stimulated by bradykinin.

METHODS

Data for this review were obtained from a National Library of Medicine (PubMed) search, which was performed in May 2004, of the literature published in the English language from 1985 to 2004, using the search terms "angiotensin-converting enzyme," "angiotensin converting enzyme inhibitors," and "cough."

RESULTS

The incidence of ACE inhibitor-induced cough has been reported to be in the range of 5 to 35% among patients treated with these agents. However, a much lower incidence has been described in studies of patients presenting for the evaluation of chronic cough. The onset of ACE inhibitor-induced cough ranges from within hours of the first dose to months after the initiation of therapy. Resolution typically occurs within 1 to 4 weeks after the cessation of therapy, but cough may linger for up to 3 months. The only uniformly effective treatment for ACE inhibitor-induced cough is the cessation of treatment with the offending agent. The incidence of cough associated with therapy with angiotensin-receptor blockers appears to be similar to that of the control drug. In a minority of patients, cough will not recur after the reintroduction of ACE inhibitor therapy.

CONCLUSIONS

In a patient with chronic cough, ACE inhibitors should be considered as wholly or partially causative, regardless of the temporal relation between the initiation of ACE inhibitor therapy and the onset of cough. Although the cessation of therapy is the only uniformly effective treatment for ACE inhibitor-induced cough, some pharmacologic agents have been shown to attenuate the cough.

Safety of capsaicin cough challenge testing

BACKGROUND

Capsaicin, the pungent extract of red peppers, has achieved widespread use in clinical research because it induces cough in a dose-dependent and reproducible manner. Although > 2 decades of experience has led investigators to consider capsaicin cough challenge testing a safe diagnostic modality, this issue has not been specifically addressed in the literature.

STUDY OBJECTIVES

To review the published experience with capsaicin inhalation challenge testing in terms of safety.

DESIGN

Literature review and personal communication with study authors.

SETTING

Academic medical center.

RESULTS

One hundred twenty-two published studies since 1984 described 4,833 subjects (4,374 adults, 459 children) undergoing capsaicin cough challenge, with no serious adverse events reported. Subjects included healthy volunteers as well as patients with asthma, COPD, pathologic cough, and other respiratory conditions. Minor complaints described in a small fraction of studies consisted mainly of transient throat irritation. Personal communication with the authors of > 90% of the studies confirmed an absence of any serious adverse events. Furthermore, these investigators have performed thousands of additional capsaicin challenge studies not reported in the literature, also without any associated serious adverse events.

CONCLUSIONS

A review of the 20-year clinical experience has failed to uncover a single serious adverse event associated with capsaicin cough challenge testing in humans. Given the need for better antitussive therapies, capsaicin represents a vital component of future scientific inquiry in the field of cough.

Potential new cough therapies

Cough is among the most common complaints for which patients seek medical attention. Consequently, enormous expenditures are made worldwide on prescription and non-prescription cough remedies. Multiple prospective studies have shown that specific antitussive therapy aimed at the underlying aetiology of cough is highly successful. The greatest current need therefore is for more effective nonspecific antitussive therapy, whose purpose is to suppress the cough reflex and provide symptomatic relief regardless of the underlying mechanism. Such therapy is particularly required for prolonged cough following upper respiratory tract infection, cough whose underlying aetiology is not easily treated, and idiopathic cough. Many areas of inquiry are currently ongoing that may lead to the development of novel and effective antitussive drugs.

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.

Effect of guaifenesin on cough reflex sensitivity

BACKGROUND

Guaifenesin, a commonly used agent for the treatment of cough, is termed an expectorant since it is believed to alleviate cough discomfort by increasing sputum volume and decreasing its viscosity, thereby promoting effective cough. Despite its common usage, relatively few studies, yielding contrasting results, have been performed to investigate the action and efficacy of guaifenesin.

STUDY OBJECTIVES

To evaluate the effect of guaifenesin on cough reflex sensitivity.

DESIGN

Randomized, double-blind, placebo-controlled trial.

SETTING

Academic medical center.

PARTICIPANTS

Fourteen subjects with acute viral upper respiratory tract infection (URI) and 14 healthy volunteers.

INTERVENTIONS

On 2 separate days, subjects underwent capsaicin cough challenge 1 to 2 h after receiving a single, 400-mg dose (capsules) of guaifenesin or matched placebo.

MEASUREMENTS AND RESULTS

The concentration of capsaicin inducing five or more coughs (C(5)) was determined. Among subjects with URI, mean (+/- SEM) log C(5) after guaifenesin and placebo were 0.92 +/- 0.17 and 0.66 +/- 0.14, respectively (p = 0.028). No effect on cough sensitivity was observed in healthy volunteers.

CONCLUSIONS

Our results demonstrate that guaifenesin inhibits cough reflex sensitivity in subjects with URI, whose cough receptors are transiently hypersensitive, but not in healthy volunteers. Possible mechanisms include a central antitussive effect, or a peripheral effect by increased sputum volume serving as a barrier shielding cough receptors within the respiratory epithelium from the tussive stimulus.

Cough. 4: Cough in asthma and eosinophilic bronchitis

Airway eosinophilia and cough may be associated with asthma and with non-asthmatic eosinophilic bronchitis. Whether cough variant asthma and eosinophilic bronchitis are distinct entities or a pathophysiological spectrum needs further examination.

Short- and long-term reproducibility of capsaicin cough challenge testing

The tussive agent capsaicin has achieved common usage in clinical research because it induces cough in a safe, dose-dependent, and reproducible manner. However, the reproducibility of capsaicin challenge testing has been demonstrated only in the short term (study intervals of 20 min to 14 days). In the present study, evaluation of data from several hundred cough challenges performed in the author's laboratory yielded two groups of 40 subjects. In the short-term reproducibility group, subjects underwent cough challenge at an interval of 14 days. Subjects in the long-term reproducibility group were challenged at intervals of at least 6 months (mean 16.7+/-2.4 months, range 6-62 months). All subjects were healthy adult volunteers who underwent identical cough challenge testing, which involved inhalation of incremental, doubling concentrations (microM) of capsaicin until the concentrations inducing two or more (C(2)) and five or more coughs (C(5)) were reached. Results were evaluated in terms of the percentage of subjects whose repeat studies yielded C(2) and C(5) values within one and two doubling concentrations of the initial values. Overall, reproducibility was quite good, with 90-100% of challenges yielding C(2) and C(5) values within two doubling concentrations. Short-term reproducibility of C(5) was superior to that of C(2), suggesting that C(5) is the preferred end point for trials involving serial cough challenges performed within a 14-day period.

Cough reflex sensitivity in cigarette smokers

STUDY OBJECTIVES

To evaluate cough reflex sensitivity in a population of young, healthy, male cigarette smokers.

DESIGN

Cross-sectional comparison.

SETTING

Academic medical center.

PARTICIPANTS

Twenty healthy, male current-smokers (mean [+/- SEM] age, 32.2 +/- 1.2 years).

MEASUREMENTS

Subjects underwent baseline spirometry followed by capsaicin cough challenge testing, which involved the inhalation of capsaicin in ascending, doubling concentrations until the concentrations inducing two or more coughs (C(2)) and those inducing five or more coughs (C(5)) were reached. The data were compared to those from a group of 50 healthy, male nonsmokers who had undergone identical cough challenge testing.

RESULTS

The two groups did not differ in terms of age or baseline pulmonary function. Cough sensitivity was significantly diminished in the current-smokers compared to control subjects. The mean (+/- SEM) log C(2) values in smokers and nonsmokers were 1.26 +/- 0.13 and 0.81 +/- 0.08, respectively (p = 0.004). The mean log C(5) values in smokers and nonsmokers were 2.03 +/- 0.10 and 1.20 +/- 0.08, respectively (p < 0.000001).

CONCLUSIONS

Cough reflex sensitivity is significantly diminished in young, healthy, male current-smokers compared to a similar population of nonsmokers. The mechanism of cough suppression in smokers remains speculative but may involve long-term tobacco smoke-induced desensitization of the cough receptors within the airway epithelium.

Antitussive effect of the leukotriene receptor antagonist zafirlukast in subjects with cough-variant asthma

Cough-variant asthma (CVA) occurs in a subgroup of asthmatics whose sole or predominant respiratory symptom is cough. Although bronchodilators are often sufficient to treat CVA, refractory cough may require therapy with inhaled or systemic corticosteroids. In a randomized, double-blind, placebo-controlled, crossover study, we examined the effect of a 14-day course of the leukotriene receptor antagonist zafirlukast on subjective cough score and cough-reflex sensitivity to inhaled capsaicin in eight subjects with CVA refractory to inhaled beta agonists, and in five subjects refractory to inhaled corticosteroids. Seven of eight subjects experienced significant subjective and objective improvement in cough after treatment with zafirlukast. Mean (+/- SEM) cough score improved from 7.75 +/- 0.56 to 3.25 +/- 0.84 (p = 0.0006). Cough sensitivity to capsaicin was suppressed by zafirlukast in all subjects. Patients with CVA may represent a distinct subgroup of asthmatics whose afferent cough receptors within the respiratory epithelium are hypersensitive relative to those of patients with the typical form of asthma. Zafirlukast appears to be particularly effective in treating CVA by inhibiting the sensitivity of these receptors. Leukotriene receptor antagonists may offer an alternative to corticosteroids for the treatment of CVA refractory to inhaled bronchodilators.

Ethnic and gender differences in cough reflex sensitivity

BACKGROUND

Although recent studies have suggested that the cough reflex is more sensitive in women than in men, ethnic differences in cough reflex sensitivity have not previously been investigated.

OBJECTIVES

To evaluate ethnic and gender differences in cough reflex sensitivity.

METHODS

We performed capsaicin cough challenge testing in 182 healthy volunteers of three distinct ethnic groups: Caucasian (white, non-Hispanic, of European origin), Indian (originating from the Indian subcontinent) and Chinese. The concentration of capsaicin inducing 2 or more (C2) and 5 or more coughs (C5) was determined in each subject.

RESULTS

Mean (+/-SEM) values for log C5 demonstrated that, within each ethnic group, the cough reflex was more sensitive in women: p = 0.00002 for Caucasian subjects; p = 0.003 for Indian volunteers; and p = 0.002 for Chinese subjects. Examination of C2 data yielded similar results. When subjects were evaluated by gender, multivariate analysis of variance demonstrated no ethnic differences in sensitivity to capsaicin.

CONCLUSION

Our data do not support the presence of significant ethnic differences in cough reflex sensitivity, but do confirm previous data demonstrating lower cough thresholds in women.

Effect of the cyclooxygenase-2 inhibitor celecoxib on bronchial responsiveness and cough reflex sensitivity in asthmatics

Cyclooxygenase (COX), an essential enzyme in the pathway of prostaglandin formation from arachidonic acid, exists in two isoforms. Cyclooxygenase-1 (COX-1) is expressed under normal physiologic conditions, whereas COX-2, the inducible isoform, is associated with inflammation. Recent studies have linked COX-2 induction to the asthmatic inflammatory response, but potentially beneficial results, such as enhanced production of antiinflammatory and bronchoprotective substances, may also occur. The aim of the present study was to investigate the effect of selective COX-2 inhibition on bronchial responsiveness and cough reflex sensitivity. Eight adult subjects with stable asthma underwent spirometry, bronchoprovocation challenge with methacholine, and cough challenge testing with capsaicin, before and after a 7 day course of the COX-2 inhibitor celecoxib (200 mg orally, twice daily) and placebo, in a randomized, double-blind, crossover fashion. No significant changes in pulmonary function, bronchial responsiveness, or cough reflex sensitivity were induced by celecoxib. It appears, therefore, that 1 week of therapy with celecoxib does not significantly affect basal airway tone, nor the afferent airway receptors controlling bronchoconstriction and cough. However, the results of this trial cannot be extrapolated to subjects with severe asthma, or those suffering an asthmatic exacerbation. In such conditions of enhanced inflammatory response, the role of selective COX-2 inhibition remains to be elucidated.

Treatment of chronic, refractory cough with baclofen

Chronic, nonproductive cough may result from enhanced sensitivity of the cough reflex. Often, this debilitating symptom is refractory to standard antitussive therapy. Baclofen, an agonist of gamma-aminobutyric acid (GABA), has been shown, in animals, to have antitussive activity via a central mechanism. Recently, in normal subjects, we have demonstrated the ability of baclofen to inhibit capsaicin-induced cough, as well as cough due to angiotensin-converting enzyme (ACE) inhibitors. Herein, we describe two patients with chronic, refractory cough who obtained symptomatic improvement after a 14-day course of low-dose, oral baclofen, administered in a double-blind, placebo-controlled manner. In addition, both subjects demonstrated significant increases in cough threshold to inhaled capsaicin after treatment with baclofen.

Baclofen-induced cough suppression in cervical spinal cord injury

OBJECTIVE

To determine the effect of the GABA-agonist baclofen on cough reflex sensitivity in subjects with cervical spinal cord injury (C-SCI). Baclofen has been shown to inhibit the cough reflex in able-bodied volunteers.

DESIGN

Prospective, nonrandomized control trial.

SETTING

Veterans Affairs medical center with large outpatient SCI population.

PARTICIPANTS

Twelve adult males (11 outpatients) with C-SCI chronically maintained on oral baclofen for the treatment of muscle spasm.

INTERVENTION

Subjects underwent cough challenge testing with inhaled capsaicin. The concentrations (microM) of capsaicin inducing 2 or more (C2) and 5 or more (C5) coughs were determined. Mean values for log C2 and log C5 were compared with a control group of outpatients with C-SCI not receiving baclofen.

RESULTS

Subjects treated with baclofen had a significantly higher cough threshold (diminished cough reflex sensitivity) than control subjects. Mean (+/- standard error of the mean) values for log C2 in study subjects and controls were 1.28 +/- .16 and .65 +/- .15, respectively (p = .009). Mean values for log C5 in subjects receiving baclofen and in control subjects were 2.20 +/- .22 and 1.43 +/- .23, respectively (p = .024). Subjects and controls did not differ in terms of age, spirometric parameters, or duration of injury.

CONCLUSIONS

The results suggest that chronic therapy with baclofen diminishes cough reflex sensitivity in subjects with C-SCI. The clinical significance of this finding remains to be elucidated.

Effect of the GABA-agonist baclofen on bronchial responsiveness in asthmatics

Gamma-aminobutyric acid (GABA) is a central inhibitory neurotransmitter. Recently, the presence of GABA and its receptors has been confirmed in peripheral tissues, including the lungs. GABA and the GABA agonist baclofen have been shown in animal studies to inhibit airway responsiveness to various bronchoconstricting agents. The results of these investigations suggest the possibility of a role for baclofen in the therapy of human airway hyperreactivity. To investigate this question, a randomized, double-blind, placebo-controlled, cross-over study was performed to evaluate the effect of a 14-day course of oral baclofen (10 mg three times daily) on pulmonary function and bronchial responsiveness to methacholine in a group of six stable asthmatics. In five of six subjects, hyperresponsiveness was enhanced after therapy with baclofen. Mean (+/- SEM) log PC(20)pre-and post-baclofen were 0.160 +/- 0.247 and -0.223 +/- 0.282, respectively (P=0.023). Baseline pulmonary function (FEV(1)) was unaffected by baclofen. The mechanism(s) underlying this apparent paradoxical enhancement by baclofen of bronchial responsiveness remains speculative, but may be relevant to the recently-proposed concept of dysfunction in asthmatics of prejunctional GABA receptors, whose normal role may be to inhibit cholinergic contraction of bronchial smooth muscle.

"Crack" cocaine-induced syndrome mimicking sarcoidosis

A 39-year-old man with a history of frequent "crack" cocaine use of several years' duration presented with progressive dyspnea. Evaluation revealed bilateral interstitial pulmonary infiltrates and hilar adenopathy, diffuse pulmonary uptake of gallium, and markedly elevated serum angiotensin-converting enzyme activity. Open lung biopsy revealed interstitial and perivascular collections of histiocytes containing refractile, polarizable material, presumably inhaled along with the cocaine. Paratracheal lymph nodes were enlarged, reactive, and contained similar polarizable material. The well-formed, non-necrotizing granulomata characteristic of sarcoidosis were not present in either tissue specimen. To our knowledge, the association of chronic crack cocaine inhalation with this constellation of clinical findings, typically seen in sarcoidosis, has not previously been described.

Cough reflex sensitivity in subjects with cervical spinal cord injury

An effective cough requires an intact cough reflex as well as adequate respiratory muscle function to generate elevated intrathoracic pressures. Since the major muscles of expiration are innervated by the first thoracic segment and below, transection of the cervical spinal cord results in severely compromised expiratory function and cough. To investigate the effects of cervical spinal cord injury (C-SCI) on cough reflex sensitivity, we measured responsiveness to inhaled capsaicin in 12 male subjects with chronic C-SCI and compared findings to those from a control group of 50 able-bodied men. The concentrations (microM) of capsaicin inducing two or more (C2) and five or more coughs (C5) did not significantly differ between the two groups. Mean (+/- SEM) values for log C2 in subjects with C-SCI and control subjects were 0.65 +/- 0.15 and 0.87 +/- 0.07, respectively (p = 0.15). Mean values for log C5 in subjects with C-SCI and control subjects were 1.43 +/- 0.23 and 1.41 +/- 0.08, respectively (p = 0.94). We conclude that cough reflex sensitivity is preserved after C-SCI, and that ineffective cough in this population results primarily from the loss of innervation of respiratory muscles.

Effect of zafirlukast on cough reflex sensitivity in asthmatics

In patients with asthma, increased sensitivity of airway sensory nerves may be involved in producing bronchospasm and cough. To evaluate the effect of a leukotriene-modifying agent on cough reflex sensitivity, we measured the cough response to inhaled capsaicin before and after a 1 4-day course of therapy with zafirlukast, a cysteinyl leukotriene receptor antagonist, in a group of stable asthmatics. The concentration of capsaicin inducing two or more (C2) and five or more (C5) coughs was not altered by zafirlukast, even in those subjects demonstrating a significant change (increment or decrement) in forced expiratory volume in 1 sec (FEV1). These findings support previous evidence that cough and bronchoconstriction are modulated by distinct neural pathways.

The influence of gender on cough reflex sensitivity

BACKGROUND

The more common occurrence in women of cough due to angiotensin-converting enzyme inhibitors raises the possibility of gender-related differences in the sensitivity of the cough reflex. Of two recent studies that evaluated cough response to inhaled capsaicin in normal subjects, one demonstrated heightened sensitivity of the cough reflex in women compared with men, while the other revealed no gender-related differences. To further investigate this question, we reviewed our experience with cough challenge testing in normal volunteers.

STUDY OBJECTIVE

To compare cough reflex sensitivity in healthy adult female and male subjects.

DESIGN

Retrospective data analysis.

SETTING

Academic medical center.

PARTICIPANTS

One hundred healthy volunteers (50 male, 50 female).

INTERVENTIONS

Subjects inhaled capsaicin in ascending, doubling concentrations until the concentration inducing five or more coughs (C5) was reached. In addition, the concentration inducing two or more coughs (C2; cough threshold) was measured.

RESULTS

Mean log C5 was significantly lower in women than in men: 1.02+/-0.09 (SEM) microM vs 1.41+/-0.08 microM, respectively (p=0.002). Log C2 (cough threshold) was also significantly lower in female subjects: 0.534+/-0.068 microM vs 0.870+/-0.065 microM in male subjects (p=0.00058).

CONCLUSION

Healthy women have a more sensitive cough reflex than do healthy men. The reasons for this significant gender difference remain to be elucidated, but may involve a heightened sensitivity, in women, of the sensory receptors within the respiratory tract that mediate cough.

Inhibition of capsaicin-induced cough by the gamma-aminobutyric acid agonist baclofen

Gamma-aminobutyric acid (GABA) is a central inhibitory neurotransmitter that also exists in the lungs. The GABA-agonist baclofen has been shown to have antitussive activity via a central mechanism in animals. Recently it was demonstrated that a 14-day course of baclofen given three times daily significantly inhibits the cough reflex in healthy volunteers. Because of the prolonged antitussive effect of baclofen that has been previously observed, the present study was conducted to evaluate the antitussive effect of low-dose, oral baclofen given once daily. Forty-one healthy volunteers were randomly assigned in a double-blind manner to receive a 28-day course of baclofen, either 10 mg or 20 mg once daily, or placebo. Subjects underwent cough challenge testing with inhaled capsaicin to establish baseline cough reflex sensitivity, and subsequently after 14 and 28 days of therapy. Subjects receiving baclofen 20 mg daily demonstrated significant inhibition of cough sensitivity after 14 days and after 28 days of therapy compared with baseline. Neither placebo nor baclofen 10 mg daily had a significant effect on cough sensitivity. No serious side effects were experienced by any study participant. These results confirm the recent observation that baclofen has significant antitussive activity in humans. Further, once-daily administration of a relatively low dose of baclofen is sufficient to achieve significant cough inhibition, although at least 14 to 28 days of therapy may be required to attain maximal antitussive effect. These results support further investigation of baclofen or other GABA-agonists as potential therapeutic agents for chronic, nonproductive cough.

Antitussive effect of the GABA-agonist baclofen

BACKGROUND

gamma-Aminobutyric acid (GABA) is a central inhibitory neurotransmitter that also exists in peripheral tissues, including the lung. The GABA-agonist baclofen has been shown, in animal studies, to inhibit cough via a central mechanism, but has not been investigated in humans (to our knowledge).

STUDY OBJECTIVE

To evaluate the antitussive effect of baclofen in normal human subjects.

DESIGN

Randomized, double-blind, placebo-controlled study.

SETTING

Academic medical center.

PARTICIPANTS

Twenty healthy, adult volunteers.

INTERVENTIONS

Subjects underwent cough challenge with inhaled capsaicin before and after a 14-day course of baclofen, 10 mg three times daily, or placebo. Capsaicin cough threshold (C5) was defined as the concentration of inhaled capsaicin inducing five or more coughs.

RESULTS

Subjects receiving baclofen (n=10) demonstrated a significant elevation of capsaicin cough threshold compared with placebo subjects (n=10). Mean delta log C5 after treatment was 0.48+/-0.19 (SEM) for the baclofen group, and -0.06+/-0.12 for the placebo group (p=0.024). Six of 10 subjects receiving baclofen, but none of the 10 subjects receiving placebo, demonstrated a fourfold or greater increase in capsaicin cough threshold (p=0.0054).

CONCLUSION

The antitussive activity of low-dose, oral baclofen demonstrated in this study supports further investigation of this drug, or other GABA-agonists, for a potential therapeutic role in the treatment of pathologic cough.

Use of baclofen to suppress cough induced by angiotensin-converting enzyme inhibitors

OBJECTIVE

To determine whether baclofen can suppress the cough induced by angiotensin-converting enzyme (ACE) inhibitors.

DESIGN

Prospective, open-label, clinical trial of a 4-week course of low-dose oral baclofen (5 mg tid days 1-7, 10 mg tid days 8-28).

SUBJECTS

Seven patients with severe, persistent ACE inhibitor-induced cough.

SETTING

University-affiliated teaching hospital.

MAIN OUTCOME MEASURES

Study participants kept daily diaries monitoring the frequency of cough during and after completion of baclofen therapy.

RESULTS

All subjects demonstrated diminution of cough after initiation of baclofen. Initial improvement was noted by a mean of 4.0 days (range 3-6), and maximal improvement during treatment was achieved by a mean of 10.7 days (range 5-15). In addition, all subjects demonstrated persistent suppression of cough (range 25-74 d) after discontinuation of the study drug.

CONCLUSIONS

Low-dose oral baclofen therapy caused a prolonged antitussive effect in all subjects without inducing any adverse reactions. Baclofen may offer an alternative to the discontinuation of ACE inhibitor therapy in patients for whom these drugs are required.

Effect of angiotensin-converting enzyme inhibition on bronchial responsiveness

The effect of angiotensin-converting enzyme (ACE) inhibition on bronchial responsiveness has not been clearly established. Because ACE degrades bradykinin and substance P, inhibition of the enzyme may lead to accumulation of these potent bronchoconstrictors in the lung, potentially leading to enhanced bronchial reactivity or bronchospasm. Previous studies of the effect of ACE inhibition on airway responsiveness have yielded conflicting results. A randomized, double-blind, placebo-controlled study was therefore conducted to evaluate the effect of a 14-day course of oral lisinopril (10 mg for days 1-3, 20 mg for days 4-14) on bronchial responsiveness to inhaled methacholine in a group of healthy volunteers. No significant change in methacholine responsiveness occurred in any of the participants receiving lisinopril. The mean ( +/- SD) concentration of methacholine producing a decrease in FEV1 of 20% from baseline (PC20; mg/mL) was 23.3 +/- 5.0 before the study and 23.5 +/- 4.5 at the end of the study for the lisinopril group, and 23.0 +/- 4.6 before the study and 21.8 +/- 6.9 after the study for the placebo group. The 14-day course of ACE inhibitor therapy did not enhance nonspecific bronchial responsiveness in healthy volunteers.

Postobstructive pulmonary edema induced by endotracheal tube occlusion

Pulmonary edema is a well-described complication of upper airway obstruction, most commonly caused in adults by postanesthetic laryngospasm. The mechanism initiating the formation of postobstructive pulmonary edema is believed to be the markedly negative intrapleural pressure generated by a forceful inspiratory effort against an obstructed extrathoracic airway. We herein describe a young, male patient who developed pulmonary edema postoperatively, upon emergence from anesthesia, after performing repeated, forceful inspiratory maneuvers directed against an endotracheal tube on which he had bitten down, thereby occluding it. To our knowledge, such an etiology of postobstructive pulmonary edema has not previously been described.

Pneumonia due to Staphylococcus aureus in a patient with AIDS: review of incidence and report of an atypical roentgenographic presentation

Multiple defects in host defense mechanisms produce an increased incidence of community-acquired bacterial pneumonia in individuals infected with the human immunodeficiency virus. Clinical studies suggest that Staphylococcus aureus is an uncommon cause of such infections, though its incidence is increased in the setting of intravenous drug use, indwelling vascular catheter, and coexistent pulmonary Kaposi's sarcoma or pneumonia due to Pneumocystis carinii. The significantly higher incidence of S aureus pneumonia documented in autopsy series suggests that the infection frequently remains undiagnosed ante mortem. The clinical and radiologic presentation of staphylococcal pneumonia in HIV-seropositive patients is similar to that seen in immunocompetent hosts. However, atypical radiographic patterns can occur. We describe a case of S aureus pneumonia manifested as an infiltrate with focal predominance and multiple cavitary lesions. Such a radiologic appearance has not previously been described in this population. Given the likelihood that pneumonia due to S aureus is significantly underdiagnosed ante mortem, a high index of clinical suspicion is warranted.

Inhibition of bronchial hyperresponsiveness by the GABA-agonist baclofen

gamma-Aminobutyric acid (GABA) is a well-known inhibitory transmitter of the central nervous system. Recently, the presence of GABA and its receptors has been confirmed in peripheral tissues, including lung tissue. gamma-Aminobutyric acid and the GABA-agonist baclofen have been shown in animal studies to inhibit airway responsiveness to various bronchoconstricting agents. The results of these investigations suggest the possibility of a role for baclofen in the therapy of human airway hyperreactivity. We recently showed that subjects with cervical spinal cord injury (quadriplegia) uniformly exhibit hyperresponsiveness to methacholine. The interruption of sympathetic airway innervation and resultant unopposed cholinergic tone occurring after transection of the cervical spine are thought to explain this phenomenon. We compared bronchial responsiveness with methacholine (PC20) in a control group of otherwise healthy quadriplegic nonsmokers (n = 8) with a similar group of subjects (n = 6) maintained on baclofen for the relief of muscle spasm. Mean PC20 (mg/ml) among the control group was 1.42 +/- 1.6(SD) vs 15.0 +/- 9.1 in the baclofen group (p = 0.001). The inhibition of bronchial hyperresponsiveness in subjects with cervical spinal cord injury maintained on chronic baclofen therapy suggests the drug's ability to block neuronal acetylcholine release within airways, as well as a possible direct effect on airway smooth muscle. This action of baclofen, along with its documented ability in animal lung to inhibit release of other inflammatory mediators, supports further investigation of this drug as a potential therapeutic agent for asthma treatment.