Optimizing Drug-Drug Interaction Studies: Insights from a Decade of Research and Emerging Trends
Drug-drug interactions (DDIs) remain one of the most critical considerations in clinical pharmacology. Mismanaged or unrecognized DDIs can lead to serious consequences, including increased morbidity and mortality among patients. As the pharmaceutical landscape evolves, so too must our strategies for assessing and mitigating these risks.
In this blog, Emily Dodds, Research Fellow, Scientific Consulting, explores the fundamentals of DDIs, best practices for study design, and how Quotient Sciences supports clients to conduct safe and effective DDI clinical pharmacology studies.
What is a drug-drug interaction?
Drug-drug interactions occur when one drug alters the pharmacokinetics and potentially the pharmacodynamics of another, commonly by impacting the absorption, distribution, metabolism, or excretion (ADME) of one or both compounds in the body.
Since these interactions can compromise drug efficacy and safety, DDI studies are an essential component of regulatory submissions and can be used to inform prescribers about necessary dose adjustments to ensure patient safety.
What determines the need for a DDI study?
The first question is simple: Do we need a DDI study?
Drug developers are ultimately looking to understand if a drug is either influenced by interaction or the source of interaction. Early in vitro assessments often reveal whether a drug is affected by ("object") or causes ("precipitant”) such interactions.
Key indicators include:
Enzyme involvement: If a specific enzyme contributes more than 25% to drug elimination, it warrants investigation
Transporter pathways: Hepatic, biliary, or renal elimination routes exceeding 25% signal the need for transporter studies
Polypharmacy considerations: Understanding patient comorbidities and likely co-medications can highlight real-world interaction risks
How are effective DDI studies designed by Quotient Sciences?
Quotient Sciences have been conducting Phase 1 clinical pharmacology programs for over 35 years, and we have consulted on and conducted over 80 DDI studies in the past decade at both our Nottingham and Miami clinics. While DDI studies often follow a standard schematic, optimizing study design is crucial for efficiency and accuracy.
A typical DDI study involves monitoring trial participants through several phases of clinical testing:
Reference Period: Single-dose administration of the object drug
Washout: Clearing the drug before the next phase
Steady-State Dosing: Multiple doses of the precipitant to achieve maximal inhibition or induction
Test Period: Co-administration of both drugs to assess pharmacokinetic changes
Most studies use an open-label, two-period crossover design in healthy volunteers. However, nuances such as probe selection, dosing strategies, and duration depend on regulatory guidance and literature evidence.
What are cocktail DDI studies?
Cocktail DDI studies allow simultaneous assessment of multiple enzymes and or transporters by administering a combination of probe drugs. Validated cocktails such as Geneva, Basel, and Cooperstown have been developed to ensure no interference between probe drugs. This approach reduces the need for multiple separate studies, saving time and resources, whilst still prioritizing data quality.
However, recent research reveals a disconnect between validated cocktails and real-world practice. Of 122 cocktail studies published between 2014 and 2024, only 17 matched validated combinations. This gap illustrates the current trends in cocktail DDI design, and suggests opportunities for greater alignment between regulatory recommendations and clinical implementation.
What are some trends and challenges in DDI research?
Our systematic review of the past decade uncovered several notable trends:
Enzyme-focused studies dominate: CYP enzymes are far more frequently assessed than transporters, reflecting historical priorities and the availability of transporter-specific probes
Declining trial numbers: Cocktail DDI studies have decreased over the past decade, influenced by COVID-19 disruptions, evolving regulatory guidance, and economic pressures. Cocktail DDI studies may not form a part of every molecule’s development; however, we would often advise drug developers to adopt this study type when a critical data review indicates efficiencies could be made compared to standard DDI approaches.
Funding constraints: Drug developers increasingly favor targeted studies over exploratory designs, relying on in vitro data to prioritize critical pathways
Application of silico pharmacokinetic (PBPK) modelling: A promising development is the adoption of PBPK modelling, enabling researchers to simulate DDI scenarios without conducting full-scale clinical trials, reducing costs and timelines whilst maintaining scientific rigor
Case study: Optimizing DDI study design
Quotient Sciences are often approached by clients looking to conduct complex, multi-part study requests. In one instance, a client proposed three separate clinical pharmacology DDI studies for the evaluation of their molecule, a therapy for use in a rare disease, involving two cocktail designs and one single-object investigation. If conducted separately, the studies would span 21 months and require approximately 36 participants.
By consolidating the two cocktail studies into one single study part and running it alongside the object cohort under a single protocol, we reduced timelines to six months and significantly cut costs. This optimization underscores the importance of strategic design in accelerating development without compromising data integrity.
Additionally, we recently worked on a project to build a PBPK model for belomosidil, based on published ADME and bioavailability data for the drug. The model was validated against observed clinical results. The model accurately predicted outcomes for strong and moderate CYP3A inducers, demonstrating its value in scenario testing and regulatory decision-making. For more information, download our recent poster.
The future of DDI research
DDIs will remain a cornerstone of clinical pharmacology, but the methods we use to assess them are evolving. Improved in vitro assays, cocktail combinations that have been better validated, and advanced PBPK modeling offer pathways to more efficient, cost-effective research.
At Quotient Sciences, we are committed to leveraging these innovations to deliver high-quality data packages that safeguard patient health and support regulatory success. Interested to learn how we can support your next DDI study? Speak with our team to explore a tailored clinical program for your therapy.