Phase 1 (Safety and Dosage)

Safety is the cornerstone of every clinical trial, especially during early-phase drug development where human exposure to a new chemical or biological entity occurs for the first time. In Phase 1 studies, Safety Monitoring Boards (SMBs) and Safety Review Committees (SRCs) play vital roles in safeguarding participant wellbeing and guiding dose escalation. These groups serve as independent and/or internal oversight bodies that evaluate emerging safety, pharmacokinetic (PK), and pharmacodynamic (PD) data to determine whether a study should proceed, pause, or be modified.
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Clinical pharmacologists are at the heart of early-phase drug development. Their unique skill set, combining clinical medicine, pharmacokinetics (PK), pharmacodynamics (PD), and regulatory knowledge, makes them essential members of Phase 1 trial teams. From guiding dose selection and study design to analyzing PK/PD data and supporting regulatory submissions, their expertise ensures that investigational products progress safely and efficiently. This tutorial explores the multifaceted role clinical pharmacologists play in Phase 1 trials, highlighting their contributions to study planning, execution, and data interpretation.
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Phase 1 clinical trials are governed by meticulously crafted protocols to ensure participant safety, data integrity, and regulatory compliance. Despite this, deviations from the protocol can occur due to operational, clinical, or logistical challenges. Additionally, as data emerge during trial execution, amendments may be necessary to update objectives, dosing schedules, or safety measures. In early-phase research, where risks are high and timelines tight, managing protocol deviations and amendments effectively is critical to maintaining the credibility of the study.
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First-in-Human (FIH) clinical trials are among the most critical and high-risk stages in drug development. At this point, investigational drugs are administered to humans for the first time, often based only on preclinical data. To mitigate unforeseen safety risks, many regulatory agencies mandate or strongly recommend the implementation of a sentinel dosing strategy. This approach allows for cautious evaluation of safety and tolerability before exposing additional participants. In this tutorial, we explore what sentinel dosing entails, how it’s applied, and why it’s essential in early clinical development.
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Phase 1 clinical trials are designed to explore safety, pharmacokinetics (PK), and tolerability of a new investigational drug. Given the first-in-human exposure and potential unknown risks, early stopping rules are essential safeguards built into the trial protocol. These rules provide clear, predefined criteria that guide investigators, sponsors, and safety committees in deciding whether a study should be paused or permanently terminated. This tutorial explores different types of early stopping rules—based on safety, PK data, and futility—and provides examples and best practices for implementing them in a compliant and operationally sound manner.
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Biosimilars—biologic products that are highly similar to an approved reference product—must undergo rigorous evaluation to demonstrate similarity in structure, function, and clinical performance. Phase 1 clinical trials are a cornerstone of biosimilar development and focus primarily on pharmacokinetics (PK), pharmacodynamics (PD), and immunogenicity. These studies are not designed to establish efficacy per se but to confirm that the biosimilar behaves similarly to the originator biologic in healthy subjects or patients. This tutorial explains the strategic design and regulatory expectations for Phase 1 biosimilar trials.
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In Phase 1 clinical trials—especially first-in-human studies—the primary goal is to evaluate the safety, tolerability, pharmacokinetics (PK), and sometimes pharmacodynamics (PD) of an investigational drug. While efficacy is not the main objective at this stage, placebo control is often incorporated to support data integrity, enable unbiased safety interpretation, and comply with regulatory guidance. This tutorial delves into the rationale for using placebo arms in Phase 1, when they are most appropriate, how they are structured, and the ethical and operational considerations involved.
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Long-acting injectables (LAIs) are a rapidly growing therapeutic platform offering sustained drug release and improved patient adherence across a range of indications—from mental health and contraception to infectious diseases and metabolic disorders. However, evaluating LAIs in early-phase trials introduces unique pharmacokinetic, safety, and ethical challenges. Phase 1 studies of LAIs must balance prolonged exposure risks, depot kinetics, and delayed adverse events, often requiring specialized designs and real-time monitoring. This tutorial explores the complexities of designing Phase 1 studies for long-acting injectable drugs and outlines strategies for mitigating dosing and safety risks.
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Phase 1 clinical studies are traditionally viewed as safety and pharmacokinetics (PK)-focused investigations, but they also form the backbone of any successful New Drug Application (NDA) or Biologics License Application (BLA). Regulatory agencies such as the FDA, EMA, and CDSCO closely examine Phase 1 data to assess the scientific justification for proposed dosing regimens, identify safety signals, and evaluate the overall benefit-risk profile. This tutorial provides a comprehensive look at how Phase 1 results are used in regulatory submissions and what regulators expect when reviewing this data.
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Obtaining precise and early pharmacokinetic (PK) data is essential to inform dose selection, metabolism, and safety strategies in Phase 1 clinical trials. Traditionally, human mass balance and absorption studies required high doses of radiolabeled compounds, posing ethical and operational limitations. Today, microtracer studies combined with accelerator mass spectrometry (AMS) enable detailed PK and ADME profiling using ultra-low radioactive doses in humans. This article explains how microtracer/AMS technologies work, their regulatory significance, and how they are reshaping early-phase clinical development.
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