What prescription-strength liquid cough medication can be ordered for a patient with a persistent cough, considering their age, weight, and medical history, including any underlying respiratory disease, impaired renal (kidney) or hepatic (liver) function, or history of substance abuse?

Prescription-Strength Liquid Cough Medications

For prescription-strength liquid cough suppression, order codeine-containing liquid formulations (such as codeine sulfate oral solution 10-15 mg/5 mL) or promethazine with codeine syrup, though dextromethorphan liquid at higher doses (60 mg) is equally effective with a superior safety profile and should be considered first-line. 1, 2, 3

Primary Recommendation: Dextromethorphan Liquid

Dextromethorphan liquid formulations at 60 mg dosing provide maximum cough reflex suppression and represent the safest prescription-strength option. 2, 3

• Dextromethorphan is a centrally acting non-sedating opioid that effectively suppresses the cough reflex 2, 4
• The optimal dose for maximum cough suppression is 60 mg, which is higher than typical over-the-counter preparations 2, 3
• Standard dosing is 10-15 mg three to four times daily, with a maximum daily dose of 120 mg 3
• Dextromethorphan has demonstrated efficacy in meta-analyses for acute cough with a dose-response relationship 2
• This agent has a superior safety profile compared to codeine-based products, avoiding drowsiness, nausea, constipation, and physical dependence 2, 3, 5

Alternative Prescription Options

Codeine-Containing Liquid Preparations

• Codeine liquid formulations are available but offer no greater efficacy than dextromethorphan while carrying significantly more adverse effects 1, 2, 3
• Codeine is recommended only for chronic bronchitis with short-term symptomatic relief (Grade B recommendation) 1
• Side effects include drowsiness, nausea, constipation, and risk of physical dependence 2, 3, 5
• Codeine should be reserved for cases where dextromethorphan has failed 1

Promethazine-Based Preparations

• Promethazine has no established efficacy for cough suppression and is primarily indicated for nausea and sedation 3
• Promethazine is not recommended for cough management 3

Guaifenesin Liquid (Expectorant)

• Available as a prescription-strength expectorant for productive cough 6
• Not appropriate for dry, non-productive cough suppression 6

Clinical Algorithm for Prescribing

Step 1: Determine Cough Type and Duration

• Acute cough (<3 weeks): Consider non-prescription approaches first 1
• Subacute postinfectious cough (3-8 weeks): Trial inhaled ipratropium before central antitussives 1, 3
• Chronic cough (>8 weeks): Investigate underlying causes before suppressing cough 1

Step 2: Rule Out Contraindications

• Do not suppress productive cough where secretion clearance is beneficial 2, 5
• Assess for pneumonia (tachycardia, tachypnea, fever, abnormal chest exam) before prescribing antitussives 2
• Stop ACE inhibitors if patient is taking them, as cough may resolve in 26 days 1
• Encourage smoking cessation in smokers, as this resolves cough in most cases within 4 weeks 1

Step 3: Select Appropriate Liquid Formulation

First-line: Dextromethorphan liquid 30-60 mg for symptomatic relief 2, 3, 4

• Start with 10-15 mg three to four times daily 3
• Can use single 60 mg dose for maximum suppression 2, 3
• Maximum daily dose: 120 mg 3

Second-line (if dextromethorphan fails): Codeine liquid formulations 1

• Use only for short-term symptomatic relief 1
• Monitor for adverse effects including constipation and sedation 2, 3

Step 4: Consider Adjunctive Options

• For nocturnal cough: Add first-generation sedating antihistamine liquid (diphenhydramine) 2, 3, 5
• For postinfectious cough: Trial inhaled ipratropium before central antitussives 1, 3
• For severe paroxysms: Consider short course of prednisone 30-40 mg daily after ruling out other causes 1, 3

Special Population Considerations

Patients with Renal Impairment

• No dose adjustment needed for dextromethorphan as it is hepatically metabolized via CYP2D6, not renally excreted 3

Patients with Hepatic Impairment

• Use caution with all centrally acting agents 1
• Consider lower starting doses and monitor closely 1

Patients with History of Substance Abuse

• Strongly prefer dextromethorphan over codeine to avoid opioid dependence risk 2, 3, 5
• Avoid codeine-containing preparations entirely in this population 2, 3

Elderly Patients

• Check for drug interactions, particularly with CYP2D6 inhibitors 3
• Start with lower doses and titrate as needed 3

Critical Pitfalls to Avoid

• Using subtherapeutic doses of dextromethorphan (<60 mg) may provide inadequate relief 2, 3
• Prescribing codeine when dextromethorphan would be equally effective exposes patients to unnecessary adverse effects 1, 2, 3
• Suppressing productive cough in conditions like pneumonia or bronchiectasis where clearance is essential 2, 5
• Failing to check combination products for additional ingredients like acetaminophen when prescribing higher doses 2, 3
• Not addressing underlying causes in chronic cough before resorting to suppression 1
• Using antitussives for URI-related acute cough, where they have limited efficacy (Grade D recommendation) 1

When Antitussives Are NOT Recommended

• Cough due to upper respiratory infection: Limited efficacy, not recommended (Grade D) 1
• Acute or chronic cough not due to asthma: Albuterol is not recommended (Grade D) 1
• COPD exacerbation: Treat underlying condition rather than suppressing protective cough 1
• Asthma-related cough: Treat with inhaled corticosteroids and bronchodilators, not antitussives 1

Expected Timeline and Follow-up

• Relief should begin within 30-60 minutes of administration 5
• Effects can be prolonged with 60 mg dosing 2, 3
• If no improvement after 2 weeks of appropriate treatment, reassess for alternative diagnoses 3, 5
• Cough persisting beyond 3 weeks requires full diagnostic workup rather than continued antitussive therapy 3