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Preclinical Evaluation of Drug-Drug Interaction (DDI) Potential

In its most recent in vitro drug interaction guidance update, the US Food and Drug Administration (FDA) emphasized harmony with the European Medicines Agency (EMA) and Japanese Pharmaceutical and Medical Devices Agency (PMDA) on the importance of a risk-based approach to mitigating adverse drug reactions with new compounds by evaluating drug interactions prior to first-in-human studies.

In Vitro DDI Assessment

Drug-drug interactions (DDIs) may occur when taking two (or more) drugs together results in altered efficacy or behavior of one or both drugs, potentially causing adverse effects. As drug developers shepherd their drug through the development pipeline, evaluating perpetrator and victim potential is a critical component of safety testing. Generally, these studies are guided by recommendations published by regulatory authorities, which underline the utility of in vitro experiments to predict in vivo observations, justify decisions, and inform clinical study design:

Evaluating the DDI potential of an investigational new drug involves: (1) identifying the principal routes of the drug’s elimination; (2) estimating the contribution of enzymes and transporters to the drug’s disposition; and (3) characterizing the effect of the drug on enzymes and transporters. This evaluation often starts with in vitro experiments to identify potential factors influencing drug disposition to elucidate potential DDI mechanisms and to yield kinetic parameters for use in further studies. Results of in vitro experiments, along with clinical pharmacokinetic (PK) data, provide mechanistic information that can inform the need for and proper design of potential future clinical studies.

US FDA,
Final Guidance “In Vitro Drug Interaction Studies—Cytochrome P450 Enzyme- and Transporter-Mediated Drug Interactions” January 2020

Equipped with high-quality preclinical in vitro data, drug developers can better understand their drug’s journey through a patient’s body and make informed decisions for planning further investigations, including clinical trials. This includes improved representation in volunteer patient populations by avoiding unnecessary exclusions or early evaluation of pharmacokinetic properties to better design studies addressing drug interaction potential.

Core DDI Studies: Metabolism-Mediated Interactions

Standard in vitro DDI studies can predict a compound’s likelihood to cause drug-drug interactions via up- or down-regulation of drug-metabolizing enzymes or drug transporters or their activities.

Inhibition assays are designed to predict a compound’s perpetrator potential by evaluating direct and metabolism-dependent inhibition of enzymes like cytochrome P450 (CYP) or UDP glucuronyltransferase (UGT). The consequential reduced metabolism of a victim drug could potentially lead to toxicity due to increased unmetabolized drug concentrations in plasma. In contrast, enzyme induction studies are used to measure the potential of the compound to up-regulate drug-metabolizing enzymes. The resulting increased rate of clearance for a victim drug could lead to reduced efficacy.

In vitro absorption, distribution, mtabolism, and excretion (ADME) studies can provide supportive data to preclinical evaluation of DDI potential. Metabolite characterization and identification studies allow a drug developer to find out which metabolites may be formed and if any are unique to humans or disproportionately higher in human than preclinical species. It also establishes potential involvement of different enzymes, which is critical information for the design of reaction phenotyping studies. Current guidance dictates sponsors should also perform reaction phenotyping studies to determine which enzymes contribute to the clearance of a drug candidate. This information can be helpful in later definitive studies evaluating DDI potential of a drug candidate and providing insight for clinical study design, such as safety restrictions regarding concomitant medications.

Core DDI Studies: Transporter-Mediated Interactions

Drug transporters are the proteins that deliver the compound to and from the drug-metabolizing enzymes and are equally important to evaluate. In vitro drug transport studies are additive in the assessment of DDI potential by providing information on a compound’s substrate potential and likelihood to inhibit transporters which may be key in another drug’s clearance. The FDA’s final guidance for in vitro DDI studies asserts that “coupled with appropriate in vitro-in vivo extrapolation methods […] these assays can determine if the sponsor should conduct an in vivo drug interaction study.” 

Interplay between ADME, PK, and DDI

Taking interacting drugs together can potentially delay, decrease, or enhance absorption, affect a drug’s pharmacology at the target, or influence drug metabolism or excretion. As a result, this can decrease or increase the action of either drug or both drugs, or cause […] unintended consequences.

US FDA,
“CDER Conversation: Evaluating Risk of Drug-Drug Interactions” October 2017

Potential risk of a DDI can be evaluated by looking at pharmacokinetic (PK) properties of a drug, including absorption, distribution, metabolism, and excretion (ADME). Typical DDI studies include CYP (or other drug-metabolizing enzyme) inhibition and induction studies to evaluate perpetrator/victim potential and drug transport studies to explore substrate or transporter inhibition potential. However, other supportive studies to determine ADME/PK properties can be informative as well. For example, reaction phenotyping studies give a drug developer data relating to their drug’s metabolism by elucidating which drug-metabolizing enzymes interact with a compound, but this data is directly applicable to enzyme inhibition studies because it can guide study design to incorporate the correct enzymes. 

CYP cytochrome P450 enzymes metabolize xenobiotic drugs and can be key players in a drug's risk of DDI

Similarly, drug transport studies tend to be more individualized to address various properties of the molecule and assess hepatic and renal uptake (SLC family)  and efflux (ABC family, including P-gp and BCRP)  transporters to paint a whole picture. The FDA highlights importance of using PK data to inform drug transport study design, stating that drug transporters included in substrate potential studies “should be evaluated based on ADME […] data.” 

How We Help

We offer a wide variety of studies to provide you with a well-stocked toolbox for thorough evaluation of your drug’s DDI potential. In addition to the studies described above, we can also help you find out your drug’s binding affinity to plasma proteins or red blood cells, characterize and identify metabolites, predict biologic-small molecule interaction via cytokine release, and many other options. Our offerings include in vitro and in vivo studies, consulting services, and products for in-house DMPK assays to serve you in this critical part of your journey through drug development.   

As a CRO specializing in helping drug developers identify DDI potential of their compound, we offer many products and services to give our clients the most high-value data on which to base assessment and decisions. We have been focused on guiding countless pharmaceutical developers through the complexities of nonclinical drug development for over 25 years, so we understand the value in making informed choices at each step along the path to the clinic. Missing something early in development can lead to unexpected roadblocks from doubling-back to patch up holes, restrictive labeling, or worse– late-stage clinical failure. That’s why we offer a consultative approach to develop tailored studies producing high-quality data for your program’s needs while ensuring satisfaction of regulatory requirements.

Our Core Competencies in Evaluating DDI

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