Abstract
Background
Controversies
Commonly used prescription and over-the-counter antitussive formulations that contain some combination of antihistamines (e.g., diphenhydramine), a mucolytic (e.g., guaifenesin), and/or dextromethorphan are often used for acute cough due to upper respiratory infections and acute bronchitis. Evidence for these agents in the acute setting is poor (either no better than placebo or sweet syrup) and cannot be recommended. Due to concerns about inadvertent overdose and lack of efficacy, use of these products in the pediatric setting is now being actively discouraged.
Peripherally Acting Antitussives
Sweet syrups are commonly used as cough suppressants, whether as bases for prescription elixirs (such as codeine with guaifenesin) or home remedies (honey, simple syrup). The mechanism of action is unknown; some authors hypothesize that a sweet syrup acts as a protective barrier to sensory receptors in the throat that heighten the cough reflex. A few controlled trials have shown sweet syrups reduce coughing in upper respiratory infections.
Benzonatate inhibits cough by anesthetizing stretch receptors in the respiratory tract. Its duration of action is 3–8 hours; dosed at 100–200 mg three times a day. No published controlled studies confirm its effectiveness, but multiple uncontrolled studies support its use. Side effects are uncommon but include sedation, headache, bronchospasm, and nausea. Expert opinion recommends adding it to an opioid.
Antihistamines and anticholinergics are often part of combination antitussive elixirs with or without an opioid. Anticholinergics such as hyoscyamine and scopolamine are most helpful in the setting of copious upper respiratory secretions leading to cough. See Fast Fact #109 for dosing information.
Expectorants thin bronchial secretions and ease expectoration. Examples include guaifenesin (200–400 mg every 4 hours) and nebulized acetylcysteine or hypertonic saline. Empirically they have been recommended for severe chronic wet coughs. Because they may increase fluid in the respiratory tract, they are not recommended if the cough reflex is diminished.
Nebulized local anesthetics are thought to work by anesthetizing afferent receptors in the respiratory tract. There have been no trials evaluating their effectiveness; anecdotally they have been reported to be effective for refractory cough. Published regimens include lidocaine 2% solution (5 mL nebulized every 6 hours) and bupivacaine 0.25% (5 mL nebulized every 8 hours). Bronchospasm is a potential side effect.
Other agents such as bronchodilators and corticosteroids have not been shown to be effective apart from specific indications (e.g., COPD or asthma exacerbations). Paroxetine, amitriptyline, gabapentin, and benzodiazepines have all been anecdotally reported to have efficacy in chronic refractory cough.
Recommendations
Treatment for cough should be directed at the underlying cause if feasible and consistent with a patient's prognosis and goals of care. When symptomatic treatment for a distressing cough is necessary, it is reasonable to start with an opioid product, adding benzonatate if needed. A trial of anticholinergics and expectorants for the indications described above is reasonable, but they should be stopped after a couple days if they have no effect. Sweet syrups appear to be helpful in upper respiratory infections; their role otherwise is uncertain. If these strategies fail to control distressing symptoms, other less-studied approaches such as inhaled lidocaine are appropriate.