Acute Cough PDF - January 2024

Acute Cough Daniel J.G. Thirion, BPharm, MSc, PharmD, FCSHP Date of Revision: January 23, 2024 Peer Review Date: November 22, 2023 Pathophysiology Cough is a common symptom of many respiratory diseases and is a normal physiological response aimed at protecting the respiratory tract. It is a volunta...

Acute Cough Daniel J.G. Thirion, BPharm, MSc, PharmD, FCSHP Date of Revision: January 23, 2024 Peer Review Date: November 22, 2023 Pathophysiology Cough is a common symptom of many respiratory diseases and is a normal physiological response aimed at protecting the respiratory tract. It is a voluntarily induced or involuntarily activated reflex arc that can be triggered by a wide range of chemical and mechanical stimuli. First, receptors in the head, neck and chest are stimulated. This information is then transmitted to the cough centre in the medulla via the afferent limb of the vagus nerve, resulting in increased neural activity in the efferent pathway to both the respiratory musculature and airway.​ Cough is present in many respiratory diseases. To help guide clinical assessment, it can be useful to classify cough according to duration within the following 3 categories: acute (lasting 8 wk).​ Acute cough is responsible for more than 50% of new patient attendance in the primary care setting and is the major source of consultation in pharmacy practice.​ Viral infections of the upper respiratory tract are the most common causes of acute cough. Some coughs may persist despite the resolution of infection; these subacute coughs are called “postinfectious.”​ Cough due to viral infections appears to arise from stimulation of the cough reflex in the upper respiratory tract caused by postnasal drip (referred to as upper airway cough syndrome [UACS]—formerly postnasal drip syndrome), clearing of the throat or both.​ Other frequent causes include acute bacterial sinusitis, chronic bronchitis, allergic rhinitis and rhinitis due to environmental irritants (see Table 1).​ Bordetella pertussis or B. parapertussis infection may be suspected in patients with subacute or chronic cough, or when the cough is paroxysmal or accompanied by vomiting; referral to primary care is required in these cases.​ Refer to urgent care if the patient’s breathing is compromised or if there is high fever, seizures, frequent vomiting episodes or the patient becomes dehydrated. Table 1: Causes of Acute Cough​ Common Causes of Cough Less Common Causes of Cough Asthma Bronchiectasis Chronic obstructive pulmonary disease (COPD) Cystic fibrosis Drugs, e.g., ACE inhibitors, beta-blockers, ASA or NSAIDs in sensitive Interstitial lung disease individuals Lung cancer Environmental/occupational irritants, e.g., air pollution, cigarette smoke, Psychogenic cough asbestos Unexplained cough (idiopathic) Foreign body Zenker diverticulum (esophageal pouch) Gastroesophageal reflux disease Heart failure Pulmonary embolism Rhinitis: allergic, nonallergic Sinusitis Upper airway cough syndrome (formerly postnasal drip syndrome) Upper/lower respiratory tract infection (viral or bacterial): acute or postinfectious Goals of Therapy Diagnose and treat underlying cause, when possible Alleviate symptoms Prevent complications Patient Assessment An assessment algorithm for patients presenting with cough is presented in Figure 1. Nonpharmacologic Therapy Although evidence is lacking, hydration with oral liquids and humidification of room air may be beneficial. Room humidifiers used as preventive measures should be well cleaned to avoid aerosolizing mould. Nasal saline irrigation, or nasal suctioning in young children, can help alleviate symptoms related to nasal congestion in the context of acute upper airway infections;​ the cough- related impact of nasal saline in UACS requires further evaluation. Cough drops may be beneficial in symptom relief, but they may also increase cough severity and duration. Because of conflicting evidence, no recommendations can be made at this time.​ ​ Avoid exposure to inhaled irritants such as smoke, dust, pollutants and allergens. Pharmacologic Therapy For comparative ingredients of nonprescription products, consult the Compendium of Products for Minor Ailments—Cough, Cold and Allergy Products. Treatment of underlying conditions contributing to cough is paramount. For example, in gastroesophageal reflux disease, treatment of the reflux itself can alleviate associated cough. Smokers presenting with cough are prime candidates for discussing smoking cessation strategies.​ A specific treatment is not always possible. For example, there is no cure for the viral infection that causes the common cold. Despite a lack of evidence to support their use, nonspecific treatments such as nonprescription antitussives and protussives (expectorants) are frequently used in these cases depending on the presence/absence of mucus (sputum) production; their use cannot be recommended until further evidence becomes available (see Antitussives).​ The efficacy of drugs used in the treatment of cough has been evaluated in numerous studies including many systematic reviews.​ ​ ​ They show a lack of evidence for the effectiveness of nonprescription products in terms of reducing the frequency or severity of cough in children or adults. Some studies have shown benefit; however, the positive results in these studies were often of questionable clinical relevance.​ ​ ​ Overall, there is little evidence for or against the effectiveness of nonprescription cough medicines. When counselling patients on selecting products, also consider the placebo effect, which can be significant.​ Nonprescription agents used in the management of cough are described in Table 3. Antihistamines and decongestants Products containing antihistamines are no longer recommended for the treatment of acute cough until further evidence demonstrating efficacy becomes available.​ First-generation antihistamines (e.g., diphenhydramine) may have a small effect on cough caused by upper respiratory tract infections (URTIs).​ ​ ​ ​ Their anticholinergic properties may reduce postnasal drip, which is one of the mechanisms responsible for cough in the common cold. The effect is modest, and side effects such as drowsiness, dry mouth and confusion may outweigh potential benefit.​ Second-generation antihistamines lack significant anticholinergic effects and therefore are not effective for acute cough unless secondary to allergic rhinitis (see Allergic Rhinitis).​ Decongestants (including oxymetazoline, xylometazoline, pseudoephedrine and phenylephrine) could be helpful with postnasal drip, but evidence is limited.​ Ipratropium, an anticholinergic, reduces mucus secretion in the airways and can be recommended for symptoms of rhinitis or the common cold.​ Antitussives Nonprescription antitussives act centrally to suppress cough.​ The exact mechanism is unknown; however, the brainstem is thought to be the main region where antitussive agents act to inhibit motor control of cough. Antitussives are not recommended when a cough performs a useful function. If used by a patient with a productive cough, more mucus is retained.​ Dextromethorphan and codeine are commonly used to treat cough related to URTIs, although there is little evidence for efficacy.​ ​ ​ ​ Some studies have shown that they are no more effective than placebo, while others demonstrated a modest benefit.​ ​ ​ Historically, dextromethorphan has been abused for its euphoric properties, while codeine carries a risk of dependence and addiction. Consequently, the American College of Chest Physicians (ACCP) 2006 guideline on the management of cough does not recommend centrally acting cough suppressants for cough secondary to URTIs.​ Conversely, codeine and dextromethorphan are effective for cough due to chronic obstructive pulmonary disease (COPD), suppressing cough counts by 40–60%,​ and may be used for short-term relief.​ Clofedanol (chlophedianol) has recently been reclassified as an OTC antitussive agent. It is indicated for symptomatic relief of cough. Little evidence is available for its efficacy and no data is available on the frequency of adverse events. Expectorants The protussive agents act peripherally. Guaifenesin is purported to enhance cough effectiveness by promoting the clearance of airway secretions.​ The efficacy and safety of guaiacol and ammonium chloride have not been established. Expectorants are reported to reduce sputum viscosity, permitting more effective removal of secretions from the respiratory tract.​ As with antitussives, there is a lack of evidence to support the efficacy of expectorants. They do not thin sputum nor increase sputum volume, even at doses higher than recommended.​ Adequate hydration with oral liquids and inhalation of humidified air could be considered as a protussive or “expectorant” measure.​ Other Agents Honey may be an effective cough suppressant in children and adults.​​ ​ ​ A Cochrane review concluded that honey administered before sleep is probably better than no treatment, placebo or diphenhydramine, and no different from dextromethorphan, at relieving cough symptoms.​ ​ It is also probably better than placebo or salbutamol for reducing the duration of cough.​ Honey likely improves cough frequency and severity in URTIs.​ Honey has demulcent, antioxidant and antibacterial effects. It is proposed that the demulcent effect may act to decrease cough. Because of the risk of botulism, give pasteurized honey only to immunocompetent children >1 year of age. Zinc lozenges have been used to alleviate cough due to the common cold. Studies evaluating the efficacy of zinc in common cold symptoms have yielded conflicting results, and 2 meta-analyses have concluded there is insufficient evidence to recommend zinc preparations.​ Zinc lozenges may slow recovery time and may cause adverse events including unpleasant taste, mouth irritation and nausea.​ Anesthetics such as benzocaine, phenol and menthol may reduce the sensitivity of peripheral nociceptors. They have been used as antitussives, but evidence for efficacy is poor.​ Local anesthetics could cause numbing and result in difficulty eating and swallowing. Rarely observed side effects include tingling or irritation at the site of administration and hypersensitivity reactions. Inflammatory pathways have been largely investigated to play a role in the pathophysiology of cough; however, nonsteroidal anti-inflammatory drugs (NSAIDs) were found to have no effect on cough symptoms.​ There is accumulating evidence on the modest efficacy of ivy/thyme syrups to relieve cough. However, since there is no evidence regarding their tolerability, no recommendations can be made until further studies are conducted.​ Prescription Therapy Bronchodilators such as salbutamol or formoterol are recommended only for cough due to obstructive lung disease such as asthma or COPD.​ ​ ​ Following a respiratory infection, patients sometimes develop a cough for which inhaled corticosteroids could be beneficial; the potential benefit of inhaled corticosteroids requires confirmation through further studies before making recommendations for their routine use. For the treatment of cough secondary to another medical condition, see Allergic Rhinitis and Viral Rhinitis, Influenza, Sinusitis and Pharyngitis as well as Acute Bronchitis in the Compendium of Therapeutic Choices. For cough lasting >8 weeks, see Chronic Cough in Adults in the Compendium of Therapeutic Choices. Cough in Special Populations Children Children are 4 times more likely to experience URTI-associated acute cough than adults.​ For comparative ingredients of nonprescription products, consult the Compendium of Products for Minor Ailments—Baby Care Products: Cough and Cold. Since 2008, Health Canada has required manufacturers to relabel nonprescription cough and cold medicines with certain active ingredients to indicate that they should not be used in children