FDA Draft Guidance Gastric pH-Dependent Drug Interactions with Acid-Reducing Agents

The draft guidance newly released by FDA on “Evaluation go Gastric pH-Dependent Drug Interactions with Acid-Reducing Agents: Study Design, Data Analysis, and Clinical Implications” is now available in DIDB Resource Center. Please note that you must be signed in to access.

This draft guidance describes FDA’s recommendations regarding: (1) when clinical DDI studies with acid-reducing agents are needed; (2) the design of clinical DDI studies; (3) how to interpret study results; and (4) communicating findings in product labeling.

DIDB contains absorption-based drug interaction data. The study results are presented based on the underlying mechanism. For example, there are about 450 entries on pH-dependent drugs interactions in DIDB curated from literature and NDA reviews with detailed information about PK assessment results, study design, population, formulation, dosing, and safety results

New features! New filtering option on tables, in vitro transporter data in all drug queries, and more.

DIDB has been updated with the following new features:

  • Select filter added to Table view results
  • Query results presented in Table view first
  • Revised overall effect descriptions
  • Drug queries > Objects or Precipitants now support selecting multiple drugs (previous multiple objects/precipitants queries removed)
  • In vitro transport data added to all the Drug queries including Objects, Precipitants, and Object and precipitant Pair
  • In vitro transporter IC50 and Ki queries updated and % inhibition query added
  • In vivo transporter queries now take multiple elements
  • In vitro induction now has down regulation effect
  • FDA clinical index data updated

Feel free to contact us if you experience any issues or if you have any questions or suggestions. Your feedback is always greatly valued!

FDA Draft Guidance for Clinical Drug Interaction Studies with Combined Oral Contraceptives

The draft guidance newly released by FDA on “Clinical Drug Interaction Studies Combined with Oral Contraceptives” is now available in DIDB Resource Center. Please note that you must be signed in to access.

This draft guidance focuses on evaluating the DDI potential of an investigational new drug (i.e., perpetrator) on combined oral contraceptives  (COCs; i.e., victim) during drug development and determining how to communicate DDI study results and mitigation strategies to address potential risks associated with increased or decreased exposure of COCs in labeling.

In DIDB (as of Nov 2020), there are over 600 entries evaluating COCs as an object in dedicated clinical PK studies (including PGx data). On the other hand, nearly 200 entries were curated from clinical DDI studies where COCs serve as a precipitant.

FDA Guidance for Pharmacokinetics in Patients with Impaired Renal Function

The guidance newly released by FDA on “Pharmacokinetics in Patients with Impaired Renal Function — Study Design, Data Analysis, and Impact on Dosing and Labeling” is now available in DIDB Resource Center. Please note that you must be signed in to access.

For your information, DIDB contains study results from organ impairment studies following the recommendations in the FDA guidances on impaired renal function and on impaired hepatic function. As such study design, population, degree of organ impairment, drug dosing, PK, PD, and safety results are extracted from the literature and NDAs/BLAs reviews and entered in DIDB.

Mechanisms and clinical relevance of pharmacokinetic-based clinical drug-drug interactions for drugs recently approved by the US Food and Drug Administration

Identification and Quantification of Drugs, Metabolites, Drug Metabolizing Enzymes, and Transporters – Concepts, Methods, and Translational Sciences. Second Edition 2020, Chapter 11, 339-358.


New drug application reviews contain critical drug interaction study results with newly approved drugs tested both as victims and as perpetrators of drug-drug interactions (DDIs). Pharmacokinetic-based DDI data for drugs approved by the US Food and Drug Administration in 2013–2017 (N = 137) were analyzed using the University of Washington Drug Interaction Database. For the largest metabolism- and transporter-based drug interactions, defined as a change in exposure ≥ 5-fold in victim drugs, the mechanisms and clinical relevance were characterized. Consistent with the major role of CYP3A in drug disposition, CYP3A inhibition and induction explained a majority of the observed interactions (new drugs as victims or as perpetrators). However, transporter-mediated interactions were also prevalent, with OATP1B1/1B3 playing a significant role. As victims, 17 and 4 new molecular entities (NMEs) were identified to be sensitive substrates of enzymes and transporters, respectively. When considered as perpetrators, three drugs showed strong inhibition of CYP3A, one was a strong CYP3A inducer, and two showed strong inhibition of transporters (OATP1B1/1B3 and/or BCRP). All DDIs with AUC changes ≥ 5-fold had labeling recommendations in their respective drug labels, contraindicating or limiting the coadministration with known substrates or perpetrators of the enzyme/transporter involved. The majority of sensitive substrates or strong inhibitors were oncology and antiviral treatments, suggesting a significant risk of DDIs in these patient populations for whom therapeutic management is already complex due to poly-therapy. Pharmacogenetic studies and physiologically based pharmacokinetic models were commonly used to assess the drug interaction potential in specific populations and clinical scenarios. Finally, absorption-based DDIs were evaluated in approximately 30% of drug applications, and 14 NMEs had label recommendations based on the results.

Inhibitors of Organic Anion-Transporting Polypeptides 1B1 and 1B3: Clinical Relevance and Regulatory Perspective


Organic anion-transporting polypeptides (OATPs) 1B1 and 1B3 are the primary hepatic transporters responsible for uptake of drugs into the liver and, as such, an area of growing research focus. Currently, evaluation of these transporters as potential mediators of drug-drug interactions (DDIs) is recommended by regulatory agencies worldwide during the drug development process. Despite the growing focus on OATP1B1/1B3 as mediators of DDIs, only 2 drugs are recommended as index inhibitors for use in clinical studies, single-dose rifampin and cyclosporine, each with limitations for the utility of the resulting data. In this study a thorough analysis of the available in vitro and clinical data was conducted to identify drugs that are clinically relevant inhibitors of OATP1B1/1B3 and, from those, to select any novel index inhibitors. A total of 13 drugs and 16 combination products were identified as clinical inhibitors of OATP1B1/1B3, showing significant changes in exposure for sensitive substrates of the transporters, with strong supporting in vitro evidence. Although none of the identified inhibitors qualified as index inhibitors, this study confirmed the utility of cyclosporine and single-dose rifampin as index inhibitors to evaluate the effect of broad, multiple-pathway inhibition and more selective OATP1B1/1B3 inhibition, respectively.