Background: Chronic respiratory diseases (CRDs) are increasing in prevalence, as reported by the
World Health Organization (WHO). Patients with CRDs usually require co-administration of multiple drugs
due to the complex pathogenic mechanisms of CRDs and the existence of concomitant diseases. Polypharmacy
(co-administration of more than four medications) is the main risk factor of the occurrence of drug-drug interactions
(DDIs) that may lead to reducing treatment efficacy and/or increasing adverse effects.
Methods: This literature-based review focuses on metabolism-based DDIs, the most prevalent DDIs responsible
for difficulties in therapeutic management in patients with CRDs.
Results: Clinically relevant metabolism-based DDIs occur between drugs used for the treatment of respiratory
diseases (corticosteroids, orally inhaled bronchodilators, methylxanthines, anti-leukotrienes, antimicrobials, endothelin
receptor antagonists, phosphodiesterase inhibitors, antitussives, and antineoplastic agents) and drugs affecting
cytochrome P450 (CYP) (inducers and inhibitors). Considering alternative therapies, adjusting medication
doses, or monitoring patients during treatment are recommended to prevent the harmful consequences of
Conclusion: Providing information on clinically relevant interactions of drugs more likely prescribed in daily
practices of physicians is essential to improve patient safety. A list of known metabolism-based interactions of
drugs affecting the respiratory systems should be available for physicians engaged in the treatment of CRDs.