Phase I Clinical Trials: The Most Consequential Studies in Drug Development

Phase I clinical trials occupy a unique position in drug development. They are the smallest studies — typically 20 to 80 participants, sometimes fewer — and the shortest in duration. Yet the data they generate shapes every development decision that follows: the dose selected for Phase II, the patient population to be studied, the safety monitoring framework for the entire program, the pharmacokinetic parameters that inform every subsequent trial design. Get Phase I right and the development program builds on a solid foundation. Get it wrong and the errors propagate forward, sometimes invisibly, until they surface as unexplained variability in Phase III or as a safety signal that, properly understood, was visible in the Phase I data all along.

This article examines what Phase I studies actually require — their design principles, their dose escalation methodologies, their India-specific regulatory considerations, and the specific challenges that arise in oncology and first-in-human studies for novel mechanisms — and why the expertise applied to these small, early studies is one of the highest-leverage investments in a drug development program.

What Phase I Studies Are Designed to Accomplish

The primary objectives of Phase I studies are safety and tolerability characterization, pharmacokinetic profiling, and dose selection for further development. These objectives are straightforward in principle and demanding in execution.

Safety and tolerability encompasses the identification of adverse events across the dose range studied, characterization of dose-limiting toxicities (DLTs) — the adverse effects that constrain dose escalation — and establishment of the maximum tolerated dose (MTD) or, in oncology and certain other contexts, the recommended Phase II dose (RP2D), which may be below the MTD if the biologically effective dose is established before toxicity limits escalation.

Pharmacokinetic profiling establishes the fundamental parameters governing the drug's behavior in humans — bioavailability, volume of distribution, clearance, half-life, and the relationship between dose and exposure (AUC and Cmax). These parameters are the quantitative foundation for all subsequent dose selection — in Phase II, in special populations, in drug-drug interaction studies, and eventually in the prescribing information that will guide clinical use.

Dose selection bridges Phase I into Phase II. The dose chosen for Phase II proof-of-concept must be high enough to produce the pharmacological effect being tested, low enough to be tolerated by the patient population, and informed by the pharmacokinetic profile well enough that the exposure achieved is predictable and consistent. Poor dose selection at this transition is one of the most common — and most avoidable — causes of Phase II failure.

Dose Escalation Design: Choosing the Right Approach

The design of dose escalation in Phase I is one of the most methodologically consequential decisions in early clinical development. The classical approach — the 3+3 design, in which cohorts of three subjects receive each dose level and escalation proceeds if no more than one DLT is observed — remains the most prevalent dose escalation method, used in approximately 74% of Phase I oncology trials. Its continued dominance reflects its operational simplicity and its familiarity to investigators, ethics committees, and regulators.

But the 3+3 design has well-recognized limitations that have driven the development of alternative approaches. Its statistical properties are suboptimal — it tends to under-dose participants at the lower dose levels, over-expose participants near the MTD, and produces an MTD estimate with wide uncertainty bounds. More than 50% of Phase I oncology trials do not reach the MTD under the 3+3 framework — meaning the escalation process stops before the true dose-limiting boundary is reached, potentially identifying a recommended Phase II dose that is subtherapeutic.

Model-based dose escalation designs — including the Continual Reassessment Method (CRM), the Modified Toxicity Probability Interval (mTPI), and the Bayesian Optimal Interval (BOIN) design — apply statistical models to the accumulating toxicity data to make more efficient and more accurate dose escalation decisions. The BOIN design, for example, makes dose-selection decisions based on the interval in which the probability of toxicity for the current dose is estimated to reside, seeking a dose with probability of toxicity close to a pre-specified target level. These approaches can characterize the dose-toxicity relationship with greater precision, reduce the number of participants exposed to subtherapeutic doses, and produce MTD estimates with better statistical properties — at the cost of greater complexity in implementation and analysis.

The percentage of Phase I trials using model-based designs has increased to approximately 10% — a meaningful growth from near-zero a decade ago, driven primarily by oncology, where the ethical imperative to minimize subtherapeutic dosing of severely ill patients has been the strongest driver of methodological innovation. For sponsors and CROs conducting Phase I studies, the selection of dose escalation design should be driven by the characteristics of the compound, the patient population, and the available prior information — not by default to the most familiar approach.

First-in-Human Studies: The Special Demands of Novel Mechanisms

For truly novel compounds — new chemical entities with mechanisms of action that have not been clinically validated in humans — Phase I presents additional complexity that conventional dose escalation frameworks do not fully address.

The pre-clinical safety and pharmacology data for a novel compound are an imperfect guide to human behavior. Species differences in metabolism, receptor pharmacology, and tissue distribution mean that the relationship between animal toxicology and human safety is probabilistic rather than deterministic. The starting dose for human administration — typically derived from the most sensitive animal species using a safety factor — is conservative by design, but the conservatism reflects genuine uncertainty about how the compound will behave in human systems.

For compounds with novel mechanisms, the pharmacodynamic characterization in Phase I is as important as the toxicokinetic characterization. Demonstrating that the drug is engaging its molecular target in human tissue — through pharmacodynamic biomarkers in blood, tumor, or other accessible tissue — is what distinguishes a Phase I study that genuinely informs development strategy from one that only establishes safety and pharmacokinetics. A compound that is safely tolerated at the proposed Phase II dose but whose target engagement in humans is unconfirmed is beginning Phase II with a fundamental uncertainty that a well-designed Phase I biomarker strategy could have resolved.

This biomarker dimension of Phase I design is where scientific collaboration between the sponsor's translational science team and the clinical research organization is most critical — and where the quality of the scientific input to the Phase I protocol has the most direct impact on the informational value of the study.

Phase I in Oncology: Patient Populations and Ethical Considerations

The Phase I paradigm differs substantially between oncology and non-oncology indications — and understanding this difference is essential for designing oncology Phase I studies appropriately.

In non-oncology Phase I studies, healthy volunteers are typically enrolled — individuals without the disease of interest, selected for their normal physiology and absence of confounding medication exposure. This approach maximizes the interpretability of safety and pharmacokinetic data by minimizing biological variability.

In oncology, this approach is almost never appropriate. The toxicity profiles of anticancer agents — cytotoxic effects that are acceptable in a severely ill patient but not in a healthy individual — preclude healthy volunteer enrollment in most cases. Despite the potential risks related to the first-in-human administration of a newly developed drug, Phase I clinical trials in oncology may represent the only remaining therapeutic chance for patients ineligible for current treatments. This dual character — safety study and potential therapeutic access — shapes both the ethical framework and the practical design of oncology Phase I studies.

The informed consent process for oncology Phase I participants must address this duality honestly — neither overstating the therapeutic prospect nor understating the genuine possibility of benefit in a population with limited alternatives. Ethics committees reviewing oncology Phase I protocols scrutinize the benefit-risk framework with particular care, and the quality of the ethics submission — the clarity of the risk characterization, the robustness of the safety monitoring plan, and the adequacy of the stopping rules — directly affects the speed and outcome of the review.

Phase I in India: Regulatory Requirements and Practical Considerations

India's regulatory framework for Phase I clinical trials has evolved significantly under the New Drugs and Clinical Trials Rules 2019 and the January 2026 amendments. Understanding the current requirements — and the practical realities of Phase I conduct in India — is essential for sponsors considering India for early-phase studies.

For new drug substances discovered in India, clinical trials are required to be carried out in India from Phase I. For new drug substances discovered outside India, Phase I data already generated elsewhere is required along with the application — meaning that Phase I for foreign-discovered compounds is typically conducted first in the country of origin, with the Indian data requirement beginning at Phase II or later.

This distinction has an important practical implication. India is not typically the primary location for first-in-human studies of compounds discovered by international sponsors — the requirement to have prior Phase I data from another jurisdiction means that Phase I is typically conducted in the US, EU, or Australia, with India entering the development program at Phase II. However, for Indian-discovered new chemical entities — a growing number as India's domestic pharmaceutical innovation pipeline matures — Phase I in India is a regulatory requirement and an opportunity to build the domestic clinical data package.

The January 2026 NDCT amendments streamlined certain pre-Phase I activities — the manufacture of new drugs or investigational new drugs intended for analytical and non-clinical testing may now proceed upon submission of prior intimation to CDSCO, without requiring substantive prior approval — reducing the administrative burden at the earliest development stages. The CDSCO review timeline for Phase I applications has been reduced from 90 to 45 working days under the 2026 amendments, improving the competitive timeline for India-based Phase I programs.

Ethics committee oversight for Phase I is rigorous and comprehensive. The ICMR's national ethics guidelines specify particular requirements for first-in-human studies — including independent data safety monitoring board (DSMB) oversight, pre-specified stopping rules, and real-time safety reporting to the ethics committee during escalation. These requirements reflect the heightened duty of care appropriate for studies that are, by definition, exploring territory where prior human safety data is limited or absent.

The site requirements for Phase I clinical trials in India are more demanding than for later-phase studies. Dedicated Phase I units with 24-hour medical oversight, real-time safety monitoring capability, immediate access to emergency medical intervention, trained clinical pharmacology staff, and validated analytical laboratories for pharmacokinetic sample processing are prerequisites for conducting first-in-human studies to the standards required for international regulatory submissions.

Pharmacokinetic Study Design: The Technical Foundation of Phase I

The pharmacokinetic component of Phase I — the systematic characterization of drug exposure across dose levels and over time — is technically demanding in ways that require bioanalytical, clinical pharmacology, and statistical expertise to execute correctly.

The sampling strategy — the timing and frequency of blood draws across the PK profile — must be sufficient to characterize the complete concentration-time curve with adequate resolution to estimate the key PK parameters (Cmax, Tmax, AUC, t½, clearance, volume of distribution) without being so intensive as to create an unacceptable participant burden or logistical impossibility at the clinical site.

The bioanalytical method — the assay used to measure drug concentrations in plasma or other biological matrices — must be validated to regulatory standards before clinical samples can be analyzed. Method validation per FDA, EMA, and ICH M10 bioanalytical method validation guidelines involves demonstrating selectivity, sensitivity, linearity, accuracy, precision, dilution integrity, and stability under the conditions in which samples will be collected, stored, and analyzed. A poorly validated bioanalytical method generates PK data that cannot be relied upon — potentially invalidating the study's most fundamental outputs.

The population PK analysis that increasingly supplements or replaces intensive sampling designs in later Phase I cohorts requires statistical modeling expertise and software proficiency that must be pre-specified in the statistical analysis plan and executed by appropriately qualified biostatisticians.

Conclusion

Phase I clinical trials are the smallest and the most consequential studies in drug development. The dose escalation decisions made in Phase I determine what dose goes into Phase II. The pharmacokinetic parameters established in Phase I inform dose selection for every subsequent study. The safety profile characterized in Phase I defines the monitoring framework for the entire program. And the biomarker strategy built into Phase I — or absent from it — determines whether Phase II begins with confirmed target engagement or with a fundamental mechanistic uncertainty.

Executing Phase I well requires scientific expertise, clinical pharmacology capability, bioanalytical rigor, regulatory knowledge of the applicable frameworks, and the clinical operations infrastructure to conduct intensive studies with the safety monitoring and data quality that first-in-human research demands.

At Genelife Clinical Research, we support Phase I clinical programs for small molecule drugs — from regulatory strategy and protocol design through clinical execution, pharmacokinetic analysis, safety reporting, and clinical study report preparation — in India and for international regulatory submissions.

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To learn more about Genelife's Phase I and early clinical development capabilities, visit genelifecr.com.

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India's 2026 Clinical Trial Regulatory Reforms: What Small Molecule Sponsors Need to Know — and What Has Not Changed

In January 2026, India's Ministry of Health and Family Welfare published sweeping amendments to the New Drugs and Clinical Trials Rules 2019 — the governing framework for drug development and clinical research administered by CDSCO under the Drugs Controller General of India. According to CDSCO, the drug development lifecycle will see a minimum saving of 90 days. The amendments are now in effect and their impact on the country's pharmaceutical ecosystem is already being felt.

The coverage of these amendments in the pharmaceutical press has been enthusiastic — and in some cases, has created expectations that exceed what the reforms actually deliver. For international sponsors evaluating India as a clinical research destination, and for domestic pharmaceutical companies planning their development programs, an accurate understanding of what the 2026 amendments changed — and what they deliberately did not change — is more practically valuable than a headline summary.

This article provides that accurate understanding.

What the 2026 Amendments Actually Changed

The Prior Intimation Pathway — The Centerpiece of the Reform

The centerpiece of the reform is a deceptively simple shift: replacing the requirement for a formal test license with an online prior-intimation mechanism for most low-risk drug development and manufacturing activities.

Under the previous NDCT Rules, any company wishing to produce small quantities of a new or investigational drug — for research, non-clinical testing, analytical work, or bioequivalence studies — had to obtain prior manufacturing permission from CDSCO's Central Licensing Authority. This was an administrative approval process with its own timeline, documentation requirements, and potential for query-and-response delays. For a company managing multiple development programs simultaneously, the cumulative administrative burden was significant.

Under the amended Rule 52, the manufacture of a new drug or investigational new drug intended for analytical and non-clinical testing may now proceed upon submission of prior intimation in the prescribed form to the Central Licensing Authority and receipt of acknowledgement, without requiring substantive prior approval.

The practical effect: activities that previously required waiting for formal approval — manufacturing development batches for analytical testing, conducting stability studies, running non-clinical safety studies — can now begin faster, with the administrative gateway reduced to a notification and acknowledgement rather than a substantive regulatory review.

BA/BE Studies: A Significant Efficiency Gain for Generic Development

For bioavailability and bioequivalence studies, the reform is particularly significant. Under the previous framework, even low-risk BA/BE studies required prior regulatory permission from CDSCO before they could commence. The 2026 amendment eliminates this requirement for specified categories. Companies may now initiate these studies on the basis of a simple online intimation. CDSCO estimates it processes as many as 4,500 BA/BE applications annually; the new regime is expected to substantially reduce delays across this high-volume pipeline.

For India's generic pharmaceutical industry — which generates the majority of those 4,500 annual BA/BE applications — this is a meaningful operational improvement. Faster study initiation translates into faster regulatory submissions and faster market entry. The cumulative commercial value of this acceleration, multiplied across thousands of generic development programs, is substantial.

Reduced Review Timelines: 90 to 45 Working Days

A major reform introduced under the NDCT Amendment Rules 2026 is the reduction of regulatory review timelines from 90 to 45 working days.This represents a significant improvement for sponsors working on accelerated development programs, rare disease therapies, biosimilars, or repurposed drugs where the development timeline is a critical commercial variable.

The qualification here matters, however: this is a statutory maximum, not a guaranteed outcome. The 45-working-day review window assumes a complete, well-prepared submission that does not generate significant regulatory queries. A submission that triggers query-and-response cycles — because documentation is incomplete, the clinical rationale is inadequately developed, or the ethics committee approval is not yet in place — will consume most or all of the statutory period in those cycles. The quality of the submission dossier remains the primary determinant of actual review time.

Terminology Harmonization

The 2026 amendments introduce consistent terminology across Rules 52–66, clearly distinguishing between different regulatory pathways and formalizing both prior-approval and prior-intimation routes. This harmonization, while less headline-worthy than the timeline reductions, reduces the ambiguity in the existing rules that has historically been a source of interpretation inconsistency — both within CDSCO and across the sponsor community.

What Has Not Changed — The Misreadings to Avoid

The enthusiasm with which the 2026 amendments have been received has produced some misreadings that could create problematic expectations for sponsors who act on them. Here are the most important clarifications.

Clinical Trial Approval for Phase I, II, and III Studies: Unchanged

This is the most consequential point for small molecule clinical development sponsors. The prior intimation pathway introduced by the 2026 amendments applies to manufacturing and non-clinical activities — not to clinical trial initiation. The 2026 amendment does not speed up trial approval itself. A clinical trial cannot enrol its first participant until both the DCGI's clinical trial permission and a registered Ethics Committee's approval are in place.

Phase I, II, and III clinical trial applications for new drugs still require formal CDSCO approval under the IND/CT pathway before the first participant can be enrolled. The ethics committee review process is separate, simultaneous, and also required before enrolment. Neither of these requirements has been changed by the 2026 amendments.

The practical implication: sponsors who read the reform as accelerating the pathway to enrolling the first patient in a clinical trial will be disappointed. The timeline from clinical trial application to first patient enrolled — which involves CDSCO review, ethics committee review, site activation, and participant recruitment — is not materially different under the 2026 rules than it was before.

High-Risk Drug Categories: Unchanged

High-risk drug categories — including sex hormones, cytotoxic drugs, beta-lactam antibiotics, biologics containing live microorganisms, and narcotic and psychotropic substances — continue to require prior regulatory approval. The prior intimation pathway is explicitly risk-proportionate: it applies to lower-risk activities where regulatory pre-screening adds administrative burden without proportionate safety benefit. For the categories where the risk justifies substantive pre-approval, that requirement has been maintained.

Ethics Committee Requirements: Unchanged and Strengthened

The ethics committee oversight framework that has been progressively strengthened since the 2013 clinical trial regulatory reforms remains fully in place. All clinical studies involving human participants require prior ethics committee approval from a CDSCO-registered ethics committee. The informed consent requirements, the SAE reporting timelines, the audit and inspection framework, and the participant compensation rules are unchanged.

What the 2026 Reform Means for International Sponsors

For international pharmaceutical and biotech companies evaluating India as a location for clinical development activities, the 2026 amendments improve India's competitive position in specific and well-defined ways.

Pre-clinical and manufacturing activities are faster. For programs in active pre-clinical development, the ability to begin non-clinical safety studies, analytical method development, and formulation work without waiting for manufacturing approval removes a procedural delay that could previously add weeks to the development timeline. For international sponsors running parallel programs across multiple geographies, this administrative streamlining reduces the friction of including India in the pre-clinical development pathway.

BA/BE programs are more efficient. For generic pharmaceutical companies filing ANDAs in the US or seeking generic approvals in the EU, India's BA/BE infrastructure — established clinical sites, experienced investigators, cost-competitive analytical laboratories — combined with the streamlined prior-intimation pathway makes India an even more attractive location for BE study conduct than it was before. The combination of operational excellence and reduced administrative overhead strengthens India's position as the preferred global destination for BA/BE work.

The clinical trial pathway remains what it was — rigorous and requiring quality preparation. International sponsors should calibrate their India timelines accordingly. The clinical trial application process, while operating under a reduced statutory maximum of 45 working days, still requires a complete, high-quality submission. The ethics committee review runs in parallel and has its own timeline. Site activation, investigator contracting, and participant recruitment follow approval. Building these realistic timelines into program planning — rather than assuming that the 2026 reforms have transformed India into a low-friction regulatory environment for clinical trial initiation — produces more reliable project plans and more credible investor timelines.

The Broader Context: India's Regulatory Trajectory

The 2026 NDCT amendments do not stand alone. They are the latest step in a regulatory reform trajectory that has been building since the early 2010s — a sustained effort to modernize India's clinical research regulatory framework while maintaining the safeguards appropriate to a country that hosts a significant and growing proportion of global clinical development activity.

The reform is explicitly risk-proportionate: lighter regulation for lower-risk activities and maintained oversight where the stakes are higher. This principle — which aligns with the risk-based regulatory philosophy that the FDA, EMA, and ICH have been promoting globally — represents a genuine maturation of India's regulatory thinking, not merely a simplification of procedure.

For the international clinical research community, the direction of India's regulatory evolution is as important as any specific amendment. A regulator that is progressively aligning its framework with international risk-based principles, reducing administrative overhead for low-risk activities while maintaining rigorous oversight for high-risk ones, and committing to shorter review timelines is a regulator that is building confidence for long-term partnership.

The 2026 amendments are a meaningful step in that direction. Their appropriate value for sponsors is as evidence of that trajectory — not as a transformation of India's regulatory landscape into something categorically different from what it was before.

Practical Guidance for Sponsors

For generic pharmaceutical companies and BA/BE programs: The prior intimation pathway is immediately beneficial. If your development pipeline includes BA/BE studies for ANDA or generic regulatory submissions, the 2026 amendments remove a meaningful administrative delay. Engage a CRO partner familiar with the new SUGAM portal procedures and the intimation documentation requirements to ensure a smooth transition to the new pathway.

For new chemical entity sponsors planning Indian Phase II or III sites: The clinical trial approval pathway is unchanged. Build your India site activation timeline on realistic CDSCO review expectations — quality submission plus 45-working-day statutory maximum, with ethics committee review running in parallel. A well-prepared, complete submission to both CDSCO and the ethics committee simultaneously is the most effective timeline optimization available.

For Indian pharma companies with domestic NCE programs: The combination of the prior intimation pathway for pre-clinical work and the reduced 45-working-day review timeline for clinical trial applications is genuinely beneficial. The most important factor in realizing these improvements is submission quality — a complete, well-documented application that does not generate avoidable queries from CDSCO reviewers.

For international sponsors considering India for Phase I studies: The Phase I pathway remains governed by the requirement to have prior Phase I data from the country of origin for foreign-discovered compounds. The 2026 amendments do not change this. For India-discovered NCEs, however, the streamlined pre-clinical pathway improves the efficiency of the pre-Phase I development work.

Conclusion

India's 2026 NDCT amendments are a genuine improvement to the regulatory framework for drug development — meaningful, well-targeted, and consistent with the international direction of risk-proportionate regulatory reform. The savings in administrative time for pre-clinical, manufacturing, and BA/BE activities are real and practically significant.

What they are not is a transformation of India's clinical trial initiation pathway for new drug substances. Phase I, II, and III clinical trial approval remains a substantive regulatory review process that requires a complete, high-quality application and realistic timeline planning.

For sponsors who understand the reform accurately — who capture the genuine efficiencies it offers while planning clinical trial timelines on the basis of what the process actually requires — the 2026 amendments are a meaningful enhancement to India's already strong position as a global clinical research destination.

At Genelife Clinical Research, we have been navigating CDSCO's regulatory processes for 16 years and have deep operational familiarity with both the new prior intimation procedures and the clinical trial approval pathway as it functions in practice. We help sponsors build accurate, achievable timelines and prepare submissions that minimize query cycles and maximize the probability of first-cycle approval.

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To learn more about Genelife's regulatory strategy and clinical development services in India, visit genelifecr.com.

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Drug Repurposing: Why the Pharmaceutical Industry's Best New Drugs May Already Exist

 The conventional narrative of drug discovery runs in one direction: a novel compound is identified, optimized, tested, and — if everything goes well — approved. The molecule is new. The target is new. The therapeutic indication is new. The development timeline is long, the attrition is high, and the cost is enormous.

Drug repurposing runs the same process in reverse. The molecule already exists. Its safety profile in humans is already known. Its manufacturing process is established. The question is not whether it is safe to give to people — that has been answered — but whether it does something useful in a disease for which it was not originally developed.

This is not a niche strategy. Historical examples include sildenafil citrate transitioning from a cardiovascular compound to an erectile dysfunction treatment, and thalidomide shifting from a sedative to a foundational immunomodulatory agent in multiple myeloma — drugs that found their most important clinical applications not in the indications for which they were designed, but in diseases discovered through observation, serendipity, and scientific curiosity. These are not outliers. They are the clearest illustrations of a principle that the pharmaceutical industry is now pursuing systematically: the biology of existing drugs is richer than their approved labels suggest.

Why Drug Repurposing Has Accelerated

Several converging forces have made drug repurposing more scientifically tractable and more commercially attractive than at any previous point in the industry's history.

The explosion of biological and clinical data available for analysis has transformed what is possible. By leveraging the established safety and efficacy profiles of existing drugs, repurposing can significantly reduce the time, cost, and risk associated with traditional drug development, while providing a valuable pathway for addressing unmet medical needs. But the practical ability to identify repurposing opportunities at scale has historically been limited by the difficulty of systematically mining the relevant data — preclinical pharmacology, clinical adverse event patterns, transcriptomic signatures, network pharmacology relationships — across thousands of approved compounds simultaneously.

Artificial intelligence has changed that. AI-based platforms can analyze gene expression data, protein interaction networks, electronic health records, adverse event databases, and published literature at a scale and speed that no human team can match — identifying pharmacological relationships between approved drugs and disease pathways that would be invisible to conventional analysis. The same generative AI capabilities driving the discovery of new compounds like Rentosertib are increasingly being applied to the repurposing of existing ones.

The COVID-19 pandemic provided the most dramatic demonstration of drug repurposing at accelerated scale. The urgent search for COVID-19 treatments generated an extraordinary volume of repurposing clinical trials — with more than 4,952 clinical trials registered on ClinicalTrials.gov by March 2021, evaluating existing drugs including remdesivir, dexamethasone, baricitinib, and tocilizumab. The outcomes were mixed, but the exercise validated the clinical research infrastructure for rapid repurposing evaluation and produced genuine therapeutic discoveries — dexamethasone's role in reducing COVID-19 mortality being the most consequential.

Most recently, nitisinone — a compound originally developed as a herbicide and later approved for hereditary tyrosinemia type 1 — received FDA approval in 2025 for alkaptonuria, becoming the first targeted therapy for this ultra-rare metabolic disease after 25 years of research. The molecule was not new. The clinical need it addressed was profound and previously unmet.

The Clinical Development Advantage — and Its Limits

The most compelling aspect of drug repurposing from a development perspective is what does not need to be done. Toxicology studies across multiple species. Safety pharmacology assessments. Manufacturing process development. First-in-human dose escalation studies to establish maximum tolerated dose and pharmacokinetic profile.

For an approved drug being evaluated in a new indication, much of this pre-clinical and Phase I work is already complete. The known safety profile means that Phase II proof-of-concept studies can sometimes begin with a level of confidence in the compound's tolerability that a novel molecule cannot offer. The known pharmacokinetics mean that dose selection for the new indication can build on an established human data foundation rather than extrapolating from animal models.

Access to drugs already approved enables off-label clinical studies without the need for new GMP production, lowering trial barriers. The manufacturing supply chain is established. Regulatory submissions can reference the existing safety dossier rather than building a new one from scratch.

These advantages are real and significant. But they come with constraints that define what repurposing clinical programs need to do differently from conventional new drug development.

The indication specificity challenge. An approved drug's safety profile was characterized in a specific patient population, at a specific dose, for a specific duration of use. The new indication may involve a different patient population with different comorbidities, different concomitant medications, and different baseline organ function. The safety data from the original indication cannot be assumed to fully characterize the risk in the new indication. Phase II and III programs for repurposed drugs must include safety evaluation appropriate to the new patient population — not simply reference the existing label.

The dose may be different. The dose that was optimal for the original indication may not be optimal — or even appropriate — for the new one. Sildenafil for pulmonary arterial hypertension is dosed very differently from sildenafil for erectile dysfunction. Thalidomide's immunomodulatory applications require dose regimens that would not have been derived from its original sedative use. The clinical program for a repurposed drug must establish the appropriate dose for the new indication — which may require dose-finding studies that parallel the Phase I/II work done for the original compound.

The mechanism may be different. One of the most scientifically interesting aspects of drug repurposing is that the mechanism of action in the new indication may not be the same as in the original one. Repurposed drugs such as metformin and minoxidil demonstrate the clinical potential of repositioning strategies guided by mechanistic insight, phenotypic screening, and real-world observations — where the observed clinical effect in a new context reveals biology that was not the original pharmacological target. Understanding the mechanism of action in the new indication is important both for clinical development strategy and for regulatory submission — regulators will want to understand why the drug works in the new context, not just whether it does.

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Regulatory Pathways for Repurposed Drugs

The regulatory landscape for drug repurposing is more nuanced than the simplified narrative of "already approved, therefore easier to develop" suggests.

In the United States, a repurposed drug seeking a new indication requires a supplemental NDA if the original sponsor is pursuing the new indication, or a full NDA or 505(b)(2) application if a different company is developing the new indication. The 505(b)(2) pathway — which allows reliance on the FDA's existing findings of safety and effectiveness for a previously approved drug — is the most commonly used regulatory mechanism for repurposing by non-originators. It requires the sponsor to demonstrate that the referenced data is scientifically appropriate for the new application and to address any differences in population, dose, route, or formulation.

The FDA's stance on real-world evidence for repurposing has shifted dramatically in recent years. In December 2025, FDA eliminated a major barrier by stating that submissions need not include individual-level patient data from real-world data sources — and a May 2026 initiative opened stakeholder input on using case reports, observational studies, and registry data as components of the repurposing evidence package. This evolution makes the regulatory pathway for repurposing, particularly in rare diseases and underserved indications, meaningfully more accessible than it was even five years ago.

In India, CDSCO's framework for repurposing is evolving. For drugs already approved in India being evaluated for new indications, the regulatory pathway builds on the existing drug master file, with the clinical trial application for the new indication evaluated in the context of the established safety dossier. The January 2026 NDCT amendments, which streamlined several regulatory processes, are beneficial for repurposing programs that involve BA/BE studies or non-clinical testing — reducing the administrative overhead at the early development stages.

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India as a Location for Drug Repurposing Clinical Programs

India's clinical research infrastructure offers several specific advantages for drug repurposing programs that are worth understanding explicitly.

Disease prevalence and population diversity. Many of the most interesting repurposing opportunities — metabolic disease, fibrotic conditions, inflammatory disorders, rare genetic diseases, infectious disease — are prevalent in India at high rates, providing the patient access needed for efficient clinical proof-of-concept evaluation. Drug repurposing successes in rare diseases, including nitisinone for alkaptonuria and sirolimus for rare vascular anomalies, illustrate the value of patient populations that are rare globally but may be more accessible in India's large and diverse population.

Cost and speed for proof-of-concept. The Phase II proof-of-concept study is often the most critical and most cost-sensitive stage of a repurposing program — the study that determines whether the investment in a full Phase III program is justified. Conducting these studies in India at 40 to 60 percent of Western costs, with faster site activation and recruitment timelines, substantially improves the economics of repurposing programs that may be pursued by academic groups, patient advocacy organizations, or small biotech companies rather than large pharmaceutical sponsors.

AI-supported target identification. AI algorithms are transforming drug repurposing by revealing new therapeutic targets and mechanisms — and the integration of omics data with computational modeling enhances target identification and validation in repurposing studies. Indian research institutions and bioinformatics groups are increasingly active in this space, creating opportunities for academic-industry collaborations that identify repurposing candidates and partner with CROs to translate them into clinical programs.

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What Drug Repurposing Programs Need From a Clinical Research Partner

A CRO supporting a drug repurposing clinical program needs to bring a specific combination of capabilities that differs from conventional new drug development support.

Regulatory strategy for the new indication, building on but not simply referencing the existing approval, requires regulatory expertise in the repurposing pathway — 505(b)(2) in the US, the analogous mechanisms in the EU and India — and the scientific judgment to identify what the new clinical program must demonstrate and what it can appropriately reference from the existing dossier.

Clinical study design for proof-of-concept in the new indication requires understanding of the disease biology, the appropriate patient population, and the endpoints that are validated in the new therapeutic context — which may be quite different from the endpoints used in the original indication's development program.

Safety monitoring designed for the new population — not simply referenced from the existing label — requires pharmacovigilance expertise and the clinical judgment to identify where the safety assumptions from the original indication may not fully apply.

And the biomarker strategy — confirming that the repurposed drug is engaging its target in the new indication and producing the expected pharmacodynamic effect — is often more important in repurposing programs than in conventional development, because the mechanism of action in the new context may not be as well established as in the original indication.

Conclusion

Drug repurposing is not a shortcut. It is a scientifically rigorous and commercially intelligent strategy for accelerating the delivery of medicines to patients who need them — by building on the biological knowledge embedded in existing drugs rather than starting from zero. The savings in time, cost, and pre-clinical work are real. The clinical development work that remains — proving efficacy in the new indication, establishing the appropriate dose, characterizing safety in the new patient population, and navigating the regulatory pathway — is substantial and requires exactly the same scientific and operational rigor as conventional drug development.

The difference is that repurposing programs start from a place of greater biological knowledge. Used well, that head start can transform the economics and the timeline of clinical development in ways that benefit not just sponsors and developers, but the patients waiting for the therapies they need.

At Genelife Clinical Research, we support Phase II and III clinical programs for repurposed small molecules — from regulatory strategy and proof-of-concept study design through clinical execution, statistical analysis, and regulatory submission support — in India and for international markets.