What is an appropriate indication for administration of dextromethorphan?

A. Dry cough disrupting sleep: Dextromethorphan is a non-opioid antitussive that acts on the cough center in the medulla to suppress the cough reflex. It is most appropriate for nonproductive (dry) coughs that interfere with rest or daily activities, providing symptomatic relief without affecting mucus production. B. Copious productive cough: In a productive cough, the goal is to clear mucus from the airways. Suppressing the cough with dextromethorphan could lead to mucus retention, worsening respiratory function. Expectorants like guaifenesin are more appropriate in this scenario. C. Nasal itching and erythema: These symptoms are associated with allergic rhinitis and histamine-mediated inflammation. Antihistamines, rather than antitussives, are indicated to relieve nasal itching, sneezing, and erythema. D. Lower airway bronchospasm: Bronchospasm involves constriction of the bronchioles, as seen in asthma or COPD. Bronchodilators such as beta-agonists or anticholinergics are required to relieve airway constriction, while dextromethorphan has no effect on bronchial smooth muscle.