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# 2 Drug Interaction Guidances Out
- URL: https://www.fdaweb.com/2-drug-interaction-guidances-out/
- Published: 2020-01-23T12:00:00.000Z
- Updated: 2026-09-14T15:59:50.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5145911

FDA has published two guidances dealing with drug-drug interactions. The first guidance, *In Vitro Drug Interaction Studies—Cytochrome P450 Enzyme- and Transported-Mediated Drug Interaction*, is to help drug developers plan and evaluate studies to determine the drug-drug interaction (DDI) potential of an investigational drug product. The [document](https://www.fda.gov/media/134582/download?ref=fdaweb.com) focuses on *in vitro* approaches to evaluate the interaction potential between investigational drugs with cytochrome P450 enzymes and transporters as well as how *in vitro* results can inform future clinical DDI studies.

The guidance covers Introduction, Background, Evaluating Metabolism-Mediated Drug Interactions, Evaluating Transporter-Mediated Drug Interactions, Evaluating the DDI potential of Metabolites, Labeling Recommendations, Appendices, Abbreviations and Acronyms, and References.

The second [guidance](https://www.fda.gov/media/134581/download?ref=fdaweb.com), *Clinical Drug Interaction Studies—Cytochrome P450 Enzyme- and Transporter-Mediated Drug Interactions*, is to help sponsors of investigational new drug applications and applicants of new drug applications evaluate DDI during drug development and determine essential information to communicate in labeling. The document describes clinical studies including **(1)** the timing and design of clinical studies; **(2)** the interpretation of the study results; and **(3)** the options for managing DDIs in patients.

The agency says the two guidances together “describe a systematic, risk-based approach for evaluating DDIs and determining essential information to communicate in labeling.”

The document covers Introduction, Background, Timing of Clinical DDI Studies, Reporting and Interpreting Study Results, Labeling Recommendations, Abbreviations, and Definitions.