In a 36-year-old with a 10-day intense cough, mild‑moderate sore throat and chest wall pain, who has been taking dextromethorphan 7.5 mg twice daily and amoxicillin‑clavulanate (Augmentin) 625 mg twice daily for 5 days with only 10‑20% cough improvement, what is the most likely diagnosis and appropriate management?

Likely Diagnosis and Management

This patient most likely has post-infectious cough (possibly pertussis or atypical bacterial infection) that is inadequately treated due to subtherapeutic dextromethorphan dosing and potentially inappropriate antibiotic selection; immediate management requires escalating dextromethorphan to 30-60 mg three to four times daily, discontinuing Augmentin after completing the current course (as antibiotics have minimal benefit in viral acute bronchitis), and considering a macrolide antibiotic if pertussis is suspected. 1

Diagnostic Considerations

Post-Infectious Cough

• Cough persisting 10 days with minimal improvement suggests post-infectious cough, which typically follows an upper respiratory infection and can last 3-8 weeks 1, 2
• The chest pain is likely musculoskeletal from repetitive coughing (chest wall strain), not pneumonia, given the clinical presentation 2
• Red flags requiring immediate evaluation include: hemoptysis, significant breathlessness, tachypnea, fever with abnormal chest examination, or tachycardia—none of which appear present here 2, 3

Pertussis Consideration

• If cough has severe paroxysms or "whooping" quality, pertussis must be considered, especially given the prolonged duration and poor response to standard therapy 1
• Pertussis requires macrolide antibiotics (azithromycin or clarithromycin) and 5-day isolation from treatment start 1

Why Current Treatment Is Failing

Subtherapeutic Dextromethorphan Dosing

• The patient is taking only 7.5 mg twice daily (15 mg total daily), which is far below the therapeutic threshold 1, 2
• Standard over-the-counter dextromethorphan doses are subtherapeutic; maximum cough suppression occurs at 60 mg per dose, with recommended dosing of 30-60 mg every 6-8 hours (up to 120 mg daily) 1, 2, 3
• Doses below 30 mg provide inadequate cough suppression in post-infectious cough 1

Inappropriate Antibiotic Use

• Augmentin (amoxicillin-clavulanate) has no role in post-infectious viral cough unless bacterial sinusitis or early pertussis is confirmed 2
• Acute bronchitis is viral in 80% of cases; antibiotics decrease cough duration by only 0.5 days while exposing patients to adverse effects 4
• After 5 days of Augmentin with minimal improvement, continuing antibiotics is not indicated unless pertussis or bacterial sinusitis is suspected 2, 4

Evidence-Based Management Algorithm

Step 1: Optimize Antitussive Therapy (Immediate)

• Increase dextromethorphan to 30-60 mg every 6-8 hours (maximum 120 mg daily) for adequate cough suppression 1, 2, 3
• Caution: Check that the dextromethorphan preparation does not contain acetaminophen or other ingredients that could cause toxicity at higher doses 1, 2
• For nocturnal cough disrupting sleep, add a first-generation sedating antihistamine at bedtime (e.g., diphenhydramine), which provides both cough suppression and sedation 1, 2

Step 2: Consider Inhaled Ipratropium (First-Line for Post-Infectious Cough)

• Inhaled ipratropium bromide is the preferred first-line agent for post-infectious cough persisting after acute respiratory infection 2, 3
• Ipratropium should be tried before escalating to central antitussives like dextromethorphan 1, 2
• If ipratropium fails and cough severely impacts quality of life, consider a short course of inhaled corticosteroids 2

Step 3: Reassess Antibiotic Need

• Complete the current 5-day Augmentin course (do not stop antibiotics mid-course) 5
• Do not continue or restart antibiotics unless specific bacterial infection is confirmed 2, 4
• If pertussis is suspected (severe paroxysms, prolonged course, exposure history), switch to a macrolide antibiotic (azithromycin 500 mg day 1, then 250 mg daily for 4 days) 1

Step 4: Non-Pharmacological Measures

• Honey and lemon mixture provides symptomatic relief through central cough modulation and is as effective as many pharmacological treatments 1, 2
• Voluntary cough suppression techniques may reduce cough frequency 1, 2
• Menthol inhalation (crystals or capsules) offers short-lived acute relief for breakthrough cough episodes 1, 2

Step 5: Consider Short-Course Corticosteroids for Severe Paroxysms

• If cough has severe paroxysms that significantly impair quality of life and other treatments have failed, consider prednisone 30-40 mg daily for a short, finite period (typically 5-7 days) 1, 2
• This should only be used after ruling out other common causes and ensuring no contraindications 2

Critical Pitfalls to Avoid

• Using subtherapeutic dextromethorphan doses (<30 mg) will not provide meaningful relief 1, 2
• Continuing antibiotics beyond the current course without confirmed bacterial infection exposes the patient to unnecessary adverse effects and resistance 2, 4
• Prescribing codeine-containing antitussives, which have no greater efficacy than dextromethorphan but significantly more adverse effects (drowsiness, nausea, constipation, dependence) 1, 2
• Failing to consider pertussis in a patient with prolonged, severe cough that is not responding to standard therapy 1

When to Reassess

• If cough persists beyond 3 weeks (21 days total), a full diagnostic workup is required rather than continued antitussive therapy, as this suggests an alternative diagnosis 1, 2
• If cough worsens or new symptoms develop (fever, purulent sputum, breathlessness, hemoptysis), immediate re-evaluation for pneumonia, bacterial sinusitis, or other serious conditions is mandatory 2, 3
• Reassess in 5-7 days after optimizing dextromethorphan dosing; if no improvement, trial ipratropium or consider pertussis testing 1, 2

Patient Education

• Inform the patient that post-infectious cough typically lasts 2-3 weeks and can persist up to 8 weeks 2, 4
• Explain that the current dextromethorphan dose is too low to be effective, and the increased dose should provide better relief 1, 2
• Reassure that chest pain is likely musculoskeletal from coughing and should improve as cough frequency decreases 2
• Advise that antibiotics are unlikely to help viral post-infectious cough and should not be continued after the current course 2, 4