Drug-Drug Interaction (DDI)

Drug-Drug Interaction (DDI) describes changes in a drug's pharmacokinetics or pharmacodynamics caused by concomitant administration of another drug, potentially altering exposure levels, efficacy, or safety. DDIs may result from enzyme inhibition or induction, transporter modulation, protein binding displacement, or additive pharmacological effects. Understanding DDI risk is essential for safe prescribing, particularly in patient populations receiving multiple medications.

The pharmaceutical industry evaluates DDI potential through in vitro studies, clinical interaction trials, and modelling approaches that predict interaction magnitude under real-world conditions. Regulatory agencies require DDI assessments for new medicines, with labelling including contraindications, dose adjustment recommendations, and monitoring guidance where necessary. Biologics generally have lower metabolic DDI risk compared to small molecules, though pharmacodynamic interactions remain important, particularly in immunology and oncology combinations. As combination therapies increase and polypharmacy becomes more common, DDI evaluation remains a key component of clinical pharmacology strategy and patient safety assurance.