Eye Drops Cannot Treat Iatrogenic Cough
Eye drops have no role in the treatment of iatrogenic cough—this is a fundamental misunderstanding of both the mechanism and anatomical site of drug-induced cough. The question appears to conflate ophthalmic preparations with respiratory therapeutics, which are entirely separate pharmacological domains.
Understanding Iatrogenic Cough
Iatrogenic cough is medication-induced cough, most commonly caused by:
- ACE inhibitors account for approximately 75% of iatrogenic cough cases, presenting as a persistent dry cough that typically resolves within 1-4 days after drug discontinuation 1, 2
- Beta-blockers (including cardioselective agents), inhaled medications, cholinergic agonists, and NSAIDs can also trigger drug-induced cough through various mechanisms including bronchospasm, cyclooxygenase inhibition, or direct airway irritation 2
- The primary pathophysiology involves either direct irritation of cough receptors in the airways or bronchospasm, not ocular pathways 2
Why Eye Drops Are Not Indicated
Eye drops are designed exclusively for ophthalmic diagnostic and therapeutic purposes—they have antimicrobial, anesthetic, mydriatic, or anti-hypertensive effects limited to ocular tissues 3, 4, 5. There is:
- No anatomical connection between topical ophthalmic administration and the respiratory tract cough receptors located in the larynx, trachea, and bronchi 3
- No pharmacological mechanism by which ophthalmic preparations could suppress cough reflexes or treat airway inflammation 3, 4
- No evidence in any guideline or research supporting eye drops for respiratory symptoms 1, 6, 7, 8
Correct Management of Iatrogenic Cough
Step 1: Identify and Discontinue the Offending Agent
- Immediately discontinue ACE inhibitors if they are the suspected cause—cough typically resolves within 1-4 days, confirming the diagnosis 1, 2
- Review all medications including beta-blockers, inhaled agents, NSAIDs, and newer agents that may cause cough 1, 2
- Consider switching ACE inhibitors to angiotensin receptor blockers (ARBs), which have significantly lower cough incidence 1
Step 2: If Drug Cannot Be Discontinued
- Sodium cromoglycate may prevent ACE inhibitor-induced cough in patients who must continue the medication 2
- For patients requiring continued therapy with the offending agent, symptomatic treatment becomes necessary 1
Step 3: Symptomatic Treatment While Investigating
- Dextromethorphan 60 mg provides maximum cough suppression and is the most effective non-prescription option 7
- Benzonatate 100-200 mg three to four times daily acts peripherally to anesthetize stretch receptors in the lungs 7
- Low-dose morphine has demonstrated efficacy in refractory chronic cough when other treatments fail 1, 7
Step 4: Rule Out Alternative Causes
- Do not assume all cough in a patient on medications is iatrogenic—systematically evaluate for upper airway cough syndrome, asthma/eosinophilic bronchitis, and GERD, which together account for approximately 90% of chronic cough cases 6
- Obtain chest radiography if cough persists beyond 8 weeks or if red flags are present (hemoptysis, dyspnea, fever, weight loss) 7
Critical Pitfalls to Avoid
- Never suppress cough without investigating the underlying cause, especially in conditions like pneumonia or bronchiectasis where cough clearance is protective 1, 8
- Do not confuse diagnostic eye drops with therapeutic respiratory medications—they serve completely different purposes in different organ systems 3, 4, 5
- Recognize that habit or tic cough (previously called psychogenic cough) can mimic iatrogenic cough but requires behavioral interventions, not pharmacological suppression 1, 9
- In older adults with polypharmacy, systematically review all medications as multiple agents may contribute to cough 7