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Long before a candidate molecule reaches a human, it undergoes a series of laboratory studies to determine whether it’s safety. These nonclinical studies—pharmacokinetic, toxicology, safety pharmacology, genotoxicity, reproductive toxicity—form the scientific foundation on which every clinical trial and Regulatory submission stands. To be acceptable to regulators, the safety-relevant studies among them must be conducted under Good Laboratory Practice (GLP).
GLP compliance is often discussed in terms of inspections and SOPs, but its true purpose is more fundamental: ensuring that nonclinical safety data are reliable, traceable, reconstructable, and credible.
What Is GLP?
Good Laboratory Practice is a quality system governing the organization, conditions, and documentation of nonclinical safety studies. In the United States, the FDA's GLP regulations are codified in 21 CFR Part 58. Internationally, the OECD Principles of GLP serve as the harmonized standard recognized by most major regulators, supported by mutual acceptance of data agreements that allow studies conducted under one country's GLP to be accepted in others.
Importantly, GLP is a quality and traceability framework—not a scientific design standard. It does not dictate how a study must be designed; it dictates how it must be planned, performed, recorded, reported, and archived.
Applicability of GLP
GLP applies to nonclinical safety studies submitted to Regulatory agencies in support of marketing authorization. This typically includes pivotal toxicology, safety pharmacology, genotoxicity, reproductive and developmental toxicity, carcinogenicity, and certain ADME and bioanalytical studies that support these.
GLP does not apply to all preclinical work. Exploratory pharmacology, mechanistic biology, lead optimization, and most discovery-stage research are typically non-GLP, even when conducted carefully and to high scientific standards. Confusing GLP and non-GLP studies—either by under-classifying pivotal studies or over-classifying exploratory ones—is a common and consequential mistake.
Key Elements of a GLP Study
A GLP study has clearly defined responsibilities. The Study Director is responsible for overall scientific accountability. The sponsor and the test facility have defined roles, including for multi-site studies. The Quality Assurance Unit (QAU) operates independently of study conduct and performs inspections, audits, and report reviews.
Operational pillars include written and approved Standard Operating Procedures, characterized and stable test articles, an approved study plan or protocol, raw data captured contemporaneously, and meeting ALCOA principles (Attributable, Legible, Contemporaneous, Original, Accurate—often extended to ALCOA+), a final study report signed by the Study Director, and secure archives that retain data and specimens for the required retention period.
GLP in Practice: Beyond the Regulation
Daily GLP compliance depends more on culture than on checklists. Equipment must be qualified and calibrated; staff must be trained and retrained; deviations must be documented and assessed; computerized systems must be validated in accordance with 21 CFR Part 11 and Annex 11; and inspection readiness must be continuous, not last-minute. The strongest GLP organizations treat compliance as a property of how work is done, not as a separate audit deliverable.
Multi-site GLP studies introduce additional complexity. When a single study spans multiple test facilities or contributing scientists across different geographies, the Study Director retains overall responsibility, while Principal Investigators assume responsibility for the delegated phases. Roles, communications, and data flow between sites must be documented in the study plan and tightly controlled.
Common Findings in GLP Inspections
Recurring inspection findings include SOP deviations not properly documented or assessed, inadequate or inconsistent QAU oversight, raw-data gaps and unattributed entries, test article stability or concentration not adequately verified, computerized systems with insufficient access controls or audit trails, and archives that are not under proper environmental or access control. None of these failures is glamorous; all of them can compromise data acceptability. Regulators who detect a pattern of small findings often look harder for systemic issues, turning a routine inspection into a far more disruptive one.
GLP and Medical Writing
GLP study reports follow a defined structure: study identification, GLP statement, summary, materials and methods, results, discussion, archives, and the QAU statement. Medical writers must faithfully reflect raw data, avoid speculation beyond observed findings, and preserve the chain of evidence linking data to conclusions. Cross-references to source data and clear acknowledgment of any deviations are essential. Strong nonclinical narratives—Module 2.6, Module 4 study reports, integrated nonclinical overviews—rely on GLP reports as their underlying evidence base.
How Freyr Can Help
Freyr supports sponsors and CROs across the full spectrum of GLP-compliant medical writing and Regulatory documentation. Our nonclinical writers author and review GLP study reports, prepare nonclinical sections of CTD Modules 2.4, 2.6, and 4, perform gap assessments against 21 CFR Part 58 and OECD principles, support QA and inspection readiness, and consolidate nonclinical narratives for IND, CTA, NDA, and BLA submissions.
GLP is not a static compliance burden. It is the discipline that makes nonclinical data credible enough to be used in humans. Freyr ensures that discipline is reflected from the bench to the submission.
