ICH M12 Guideline Overview on Drug Interaction Studies

Published 31st May 2024

Overview of ICH M12 guideline on drug interaction studies Cover

Drug-drug interactions (DDI) are a common problem during drug treatment and give rise to a large number of hospital admissions as a result of medically important, sometimes serious or even fatal adverse events. Drug-drug interactions can also cause partial or complete abolishment of treatment efficacy. Several drugs have been withdrawn from the market as a result of drug-drug interactions that were only discovered post-marketing. The potential for drug-drug interactions is considered in the benefit-risk evaluation of a medicinal product. It can negatively impact this balance either through increased incidence of adverse events or reduced efficacy.

The results of DDI evaluations inform the protocols for clinical studies in patients regarding the use of concomitant drugs. Information about the interaction potential should be gained as early in drug development as practically possible to assure safety and avoid unnecessary restrictions of concomitant medications and/or exclusion of patients who require the concomitant medications in clinical studies, typically phase 2/3 studies.

The ICH M12 guideline recommends a consistent approach to designing, conducting, and interpreting enzyme- or transporter-mediated in vitro and clinical DDI studies during the development of an investigational drug. This article provides an overview of ICH M12 guideline focusing on small molecules and in vitro DDI and highlight some considerations for your DDI Gap analysis.


What comes under the scope of ICH M12 guideline principles?


General Principles

  • The guideline emphasises the critical importance of assessing the potential for drug-drug interactions (DDIs) during the development of investigational drugs. It underscores the need to evaluate both sides of the interaction coin: how the investigational drug may be affected by other drugs (as a victim) and how it may affect other drugs (as a perpetrator).
  • To comprehensively assess the DDI potential, various steps are recommended. Investigational drugs that may cause DDIs are typically assessed through in vitro experiments to understand DDI mechanisms followed by clinical studies. Drugs that cause a DDI when interacting with an investigational drug should be evaluated in a clinical mass balance study to identify principal elimination routes of the drug. In general, these studies should be conducted as early as possible in a stepwise approach to inform clinical trials with patients and ensure patient safety. However, the timing of these non-clinical and clinical studies can vary. For instance, in vitro data on the potential metabolic pathways and the enzymes an investigational drug uses for metabolism should be collected before Phase 1 trials, while mass balance study data can be obtained before Phase 3 trials.
  • Typically, in vivo animal data is collected on ADME properties to determine whetherin vitro DDI studies are needed. For example, if a drug has limited absorption or is expected to undergo significant active hepatic uptake, biliary excretion or active renal secretion as an unchanged drug, the relevant transporters should be identified in vitro before initiating clinical DDI studies in patients to avoid protocol restrictions.
  • Recommendations for the timing of non-clinical and clinical studies are provided, with predictive modelling serving as a valuable tool in assessing DDI potential.
  • The DDI assessments aid in identifying potential interactions and guiding clinical decision-making throughout drug development, ultimately ensuring the safe and effective use of investigational drugs.


In Vitro Evaluation

Evaluation of Metabolism-Mediated Interactions

Drug as a Substrate of Metabolizing Enzymes:

In general, a drug that is metabolized by multiple enzymes has a lower DDI potential than a drug that is metabolized by a single enzyme. Multiple metabolic pathways reduce the likelihood of DDIs as the closure of one metabolic pathway (e.g., by concomitant medicines) is unlikely to result in complete loss of the elimination pathway. Enzymes involved in metabolic pathways which contribute t ≥ 25% of drug elimination should be identified. The guideline indicates that CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A should be routinely evaluated using in vitro reaction phenotyping experiments to determine which enzymes metabolize the investigational drug, typically this work is performed early in development. If the investigational drug is not found to undergo significant in vitro metabolism by these major CYP enzymes, then additional assessments may be needed to understand which enzymes contribute to the overall metabolism.


This applies to CYP enzymes as well as non-CYP enzymes. These additional enzymes include but are not limited to:
  • CYP enzymes including CYP2A6, CYP2J2, CYP4F2, and CYP2E1
  • Other Phase I enzymes including aldehyde oxidase (AO), carboxylesterase (CES), monoamine oxidase (MAO), flavin monooxygenase (FMO), xanthine oxidase (XO), and alcohol/aldehyde dehydrogenase (ADH/ALDH)
  • Phase II enzymes including UDP glucuronosyl transferases (UGTs) and sulfotransferases (SULTs)


Drug as an Inhibitor of CYP enzymes:

Cytochrome P450 enzymes metabolize a significant number of small molecule drugs on the market today and, as such, are a major focus of DDI assessments. Inhibition of CYP450 is a major cause of PK-based DDIs, and drugs that are inhibitors of CYP450 enzymes reduce the clearance of other drugs that are metabolized by inhibited enzymes. Based on the ICH M12 guideline, both direct and time-dependent inhibition should be tested for DDI risk assessment for all major CYP enzymes e.g., CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A. The assay should be conducted in pooled HLM, pooled hepatocytes, microsomes from recombinant systems and should include the determination of the Ki (or the IC50) using several concentrations of the investigational drug relevant to the clinical setting.


Drug as an Inhibitor of UGTs:

The ICH M12 guideline indicated that considering the generally limited magnitude of UGT inhibition-mediated DDIs, a routine evaluation of investigational drugs to inhibit UGTs may not be warranted. If direct glucuronidation is one of the major elimination pathways of an investigational drug, it is recommended to evaluate in vitro whether the drug can inhibit UGTs including UGT1A1 and UGT2B7. When an investigational drug is to be used with another drug that is mainly metabolized by direct glucuronidation, it is recommended to evaluate the in vitro potential inhibitory effect of the investigational drug on the UGT isoform(s) responsible for the elimination of the other drug.


Drug as an Inducer of CYP enzymes:

Enzyme induction can lead to decreased efficacy and/or increased formation of toxic metabolites. The guideline recommends testing for CYP1A2, CYP2B6 and CYP3A4 induction, the first instance, as markers of induction mediated via PXR/CAR (CYP3A4, CYP2B6) and AhR (CYP1A2). If no induction of CYP3A4 enzymes is observed, evaluating the induction potential of CYP2C enzymes is not necessary because both CYP3A4 and CYP2C enzymes are induced via activation of the pregnane X receptor (PXR). These assays should be conducted in human hepatocytes from a minimum 3 individual donors and recommended readout (with the exception of CYP2C19) is changes in CYP450 mRNA levels.


Evaluation of Transporter-Mediated Interactions

Efflux transporters (P-gp and BCRP)

In vitro P-gp substrate and inhibition data are typically expected in regulatory submissions. Initial in vitro assessments are used to predict DDI potential, aiding the development of a P-gp transporter-based clinical drug interaction strategy. In addition, regulatory agencies consider BCRP, a clinically important drug transporter, and an in vitro assessment of both substrate and inhibitory potency is expected for registration.


Hepatic uptake transporters (OATP1B1 and OATP1B3) and hepatic efflux transporter (BSEP)

OATP1B1 and OATP1B3 are relevant to the hepatic uptake and disposition of drugs, and drug interactions.


Renal uptake transporters (OAT1, OAT3 and OCT2) and efflux transporters (MATE1 and MATE2-K)

OAT1, OAT3, and OCT2 are renal transporters expressed on the basolateral membrane of the renal proximal tubule. MATE1 and MATE2-K are expressed on the brush border membrane. All the aforementioned renal transporters can play a role in the active renal secretion of investigational drugs. OAT1 and 3 constitute the first step in the active renal tubular secretion of negatively charged drugs and as such are potentially implicated in renal DDIs and toxicity.

All test systems and experimental conditions for the assessment of transporther mediated DDIs should be validated and the acceptance criteria for study results should be established.


Drug as a Substrate of transporters:

  • Most investigational drugs should be evaluated in vitro to determine whether they are substrates of P-gp and BCRP, especially if biliary excretion is likely to be a major elimination pathway for the drug. In addition, if the pharmacological target of the drug is in the brain, evaluating the drug as a substrate of P-gp and BCRP can help determine whether the drug penetrates into the brain. Bi-directional transport assays with cell-based systems are usually performed.
  • Examination of whether an investigational drug is a substrate for OATP1B1 and 1B3 should be considered if hepatic metabolism or biliary excretion accounts for ≥25% of elimination of a drug or if the pharmacological target of a drug is in the liver.
  • In vitro studies to evaluate a drug as substrate of renal uptake transporters (OAT1, OAT3 and OCT2) and efflux transporters (MATE1 and MATE2-K) should be considered if a drug has renal toxicity or the drug clearance by renal active secretion is ≥25% of its systemic clearance.
  • Uptake transporters substrate evaluation is typically performed by assessing uptake into transfected cell lines compared to control cell line, or tests with and without specific inhibitor.


Drug as an Inhibitor of transporters:

  • Studies should be conducted to evaluate whether an investigational drug is an inhibitor of P-gp, BCRP, OATP1B1, OATP1B3, OAT1, OAT3, OCT2, MATE1 and MATE2-K. Evaluating the inhibition potential of a drug on other transporters such as BSEP (bile salt export pump, a hepatic efflux transporter responsible for excretion of bile acids and involved in bile acid homeostasis), MRP2, OCT1, and OATP2B1 is done on a case by case basis. In vitro studies should be performed using an experimental system whose transport activity is confirmed using probe substrates and inhibitors.
  • Recommended ratio and cut-off value for drug as inhibitor of transporters are provided in the guideline.


Drug as an Inducer of transporters:

Based on the current guideline, in vitro methods to evaluate transporter induction are not well established. If an investigational drug has been observed to be an inducer of CYP enzymes via activation of nuclear receptors such as PXR or CAR, it is likely that transporters regulated through these receptors will be induced, such as P-gp.


DDI Potential of Metabolites

Metabolite as a Substrate:

The risk of a DDI when the metabolite acts as a substrate should be evaluated for a pharmacologically active metabolite if: it contributes to in vivo target effect to a similar or greater extent than the parent drug. If plasma protein binding of the parent drug and the metabolite is high, it is preferred to determine their protein binding in the same study to reduce inter-study variability.


Metabolite as an Inhibitor:

An in vitro CYP enzyme inhibition study should be conducted if: the AUC (metabolite) ≥ 25% of AUC (parent), and also account for at least 10% of drug-related material in circulation (i.e., considered as major metabolite often determined based on radioactivity data).


Metabolite as an Inducer:

When the drug is a prodrug or a metabolite is mainly formed extra‑hepatically, in vitro evaluation of a metabolite’s induction potential on CYP enzymes is recommended if the metabolite is a major metabolite and has AUC (metabolite) / AUC (parent) ≥ 25%.


Timing of In vitro DDI Studies



ICH M12 guideline provides general recommendations on how to assess the DDI potential of investigational drugs. It is recognised that DDI assessments are often tailored to the specific drug, target patient population, and therapeutic context. Alternative methods can be used if they meet the requirements of the applicable statutes and regulations.  The focus of this guideline is on the development of new drugs, but additional DDI evaluation should be considered if new scientific information about DDI potential becomes available after drug approval.

Please contact the DLRC at hello@dlrcgroup.com with any questions you may have – our experienced team of non-clinical regulatory experts are here to assist you in the advancement of your drug interaction studies and will participate in these discussions with you to facilitate your communication with the regulatory agencies.

Stay Informed

Sign up to our bimonthly newsletter for the latest news and industry insights

    Please check this box to submit the form and agree to communications from DLRC and the storage and handling of your data, in accordance with our Privacy Policy.

    Thank you for your submission.

    Latest news

    View all