An eCTD template built to FDA requirements is a pre-structured set of folders, XML backbone files, and placeholders that mirrors the five-module Common Technical Document format the agency expects for every drug and biologic application. The framework follows ICH M4, but the FDA layers its own rules on top: a US-specific Module 1, strict PDF and file-naming conventions, mandatory study data standards, and delivery through the Electronic Submissions Gateway. Get any layer wrong and the agency can refuse to file the application before a reviewer looks at the science.
The Five Modules Your Template Has to Cover
ICH M4 divides every submission into five modules. Modules 2 through 5 are harmonized across ICH regions; Module 1 is region-specific.1European Medicines Agency. ICH Guideline M4 (R4) on Common Technical Document for Registration of Pharmaceuticals for Human Use
- Module 1 holds administrative and regional information: application forms, proposed labeling, patent information, and US-specific certifications.
- Module 2 contains the summaries and overviews reviewers use as their guide to the dossier.
- Module 3 covers quality (CMC): how the drug substance and product are manufactured, tested, and stored.
- Module 4 holds nonclinical study reports organized by pharmacology, pharmacokinetics, and toxicology.
- Module 5 holds all clinical study reports and is almost always the largest module.
What US Module 1 Adds
Because Module 1 is not harmonized, an FDA filing has to include several documents other regions don’t ask for. The FDA’s comprehensive table of contents for Module 1 covers field copy certifications, debarment certifications, financial certifications and disclosures, patent and exclusivity information, and orphan drug designations, among other items.2Food and Drug Administration. The Comprehensive Table of Contents Headings and Hierarchy The core administrative form is FDA Form 356h, which identifies the applicant and the type of submission.3Food and Drug Administration. Instructions for Filling Out Form FDA 356h ANDA filers also need a basis-for-submission statement and a comparison against the reference listed drug.
Technical Rules for the Files Inside the Template
The folder shell is the easy part. Populating it correctly is where submissions fail validation.
PDF Formatting
The FDA accepts PDF versions 1.4 through 1.7 and PDF/A-1 or PDF/A-2. Any document five pages or longer needs a hyperlinked table of contents and matching bookmarks up to four levels deep. Hyperlinks in the body should point to annotations, related sections, references, and appendices, and they should use relative rather than absolute paths, because absolute links break once the submission moves onto agency servers.4Food and Drug Administration. Portable Document Format (PDF) Specifications
Security settings and passwords are prohibited. Reviewers need to print, select text, and annotate; a locked file stalls the review while the agency asks for an unlocked copy.4Food and Drug Administration. Portable Document Format (PDF) Specifications Individual PDFs shouldn’t exceed 50 megabytes. If graphics or data push a document past that, split it into additional files with consecutive page numbering.5Food and Drug Administration. M2 eCTD Electronic Common Technical Document Specification
File and Folder Naming
The naming rules are unforgiving. File and folder names may use only lowercase letters (a–z), digits (0–9), and hyphens. No spaces, no underscores, no colons, no uppercase.6Food and Drug Administration. eCTD Backbone File Specification for Modules 2 Through 5 A single name cannot exceed 64 characters including its extension, and the full path cannot exceed 230 characters. Each file gets exactly one extension that matches its actual format. Descriptive and brief wins.
The XML Backbone
Every eCTD submission is held together by XML files that act as a machine-readable table of contents, telling regulatory software where each document lives and how the submission assembles for review. The FDA publishes a backbone specification for Modules 2 through 5 and a separate regional specification for Module 1.6Food and Drug Administration. eCTD Backbone File Specification for Modules 2 Through 5 Broken XML or a reference to the wrong file fails validation, and the submission never reaches a reviewer.
Study Data Standards
Raw datasets do not get dropped into the template as-is. The FDA requires electronic study data to conform to Clinical Data Interchange Standards Consortium (CDISC) standards, and non-conforming data can trigger a refuse-to-file action for NDAs and BLAs, or a refusal to receive for ANDAs.7Food and Drug Administration. Study Data for Submission to CDER and CBER
For clinical data in Module 5, tabulated data uses the Study Data Tabulation Model (SDTM) and analyzed data uses the Analysis Data Model (ADaM). Both need accompanying Define-XML metadata files describing the datasets. Nonclinical data in Module 4 uses the Standard for Exchange of Nonclinical Data (SEND). The SEND requirement has expanded by study type over several years; the most recent tranche became mandatory for studies started after March 2025.7Food and Drug Administration. Study Data for Submission to CDER and CBER
Submitting Through the FDA Gateway
Once the template is populated and internally validated, the package goes to the FDA through the Electronic Submissions Gateway Next Generation (ESG NextGen), a cloud-based platform that replaced the legacy ESG and serves as the single entry point for electronic regulatory submissions.8Food and Drug Administration. Electronic Submissions Gateway Next Generation (ESG NextGen)
File Size Limits
ESG NextGen has been tested to support uploads up to 1 terabyte, but each FDA center sets its own threshold by submission type. For eCTD submissions, CDER caps at 300 GB and CBER at 200 GB.9Food and Drug Administration. Center Submission Types Anything above 1 TB has to be split before upload.10Food and Drug Administration. ESG NextGen Frequently Asked Questions
Reading the Acknowledgments
After upload, the system sends a series of acknowledgment messages that track the package through delivery. ACK1 confirms the submission uploaded into ESG NextGen. ACK2 confirms transmission to the reviewing center. ACK3 and ACK4 carry the center’s response, including validation results. Not every submission generates all four; ACK2 through ACK4 are issued only when applicable.11Food and Drug Administration. Submission Acknowledgements Receiving each applicable acknowledgment without errors means the package cleared technical validation. Any error along the way needs troubleshooting before the submission can move.
Sequences After the First Filing
The initial application is not the end of the template’s life. Every supplement, amendment, annual report, and labeling change is filed as a new numbered sequence within the same eCTD structure. The original application is typically sequence 0000, the first follow-up is 0001, and each subsequent filing increments by one. Each sequence communicates only the changes: new documents are flagged as new, updated ones as replacements, withdrawn ones as deletions.
The dossier grows over time instead of being rebuilt. That works only if the XML backbone and folder structure stay consistent across every sequence. A naming or structural error in sequence 0014 can create conflicts that ripple back through the entire history, which is why sponsors managing frequent post-approval changes generally use dedicated eCTD publishing software rather than assembling submissions by hand.
eCTD v4.0 Status
Most current FDA submissions still use eCTD version 3.2.2. The agency has accepted new applications in eCTD v4.0 since September 16, 2024, but v4.0 remains optional as of early 2026. No mandatory cutover date has been announced, and future implementation phases will address forward compatibility for existing v3.2.2 applications.12Food and Drug Administration. eCTD Submission Standards for eCTD v4.0 and Regional M1 Until the FDA sets a deadline, most sponsors are keeping production submissions on 3.2.2 while monitoring the rollout.
What Triggers a Refuse-to-File
The FDA can refuse to file an NDA or decline to receive an ANDA before any substantive review. Under 21 CFR 314.101, common triggers include an incomplete application form, failure to follow the required submission format, missing information required by the Federal Food, Drug, and Cosmetic Act, an inadequate environmental assessment, missing English translations, and nonclinical studies without the required Good Laboratory Practice compliance statement.13eCFR. 21 CFR 314.101 – Filing an NDA and Receiving an ANDA For ANDAs, the agency also weighs the number and significance of deficiencies.
The financial stakes are real. The PDUFA application fee is non-refundable, and for a 2026 NDA requiring clinical data, that fee is $4,682,003.14Food and Drug Administration. Prescription Drug User Fee Amendments A formatting deficiency that costs a filer that money is the kind of mistake careful template discipline prevents.
Small Business Fee Waivers and Help
The PDUFA application fee has a narrow waiver for small businesses. To qualify, the applicant must employ fewer than 500 people including affiliates, must not have a previously approved drug product on the market, and must be submitting its first human drug application. All three conditions have to be met.15Food and Drug Administration. User Fee Waivers, Reductions, and Refunds for Drug and Biological Products The waiver is one-time: once granted, neither the applicant nor any affiliate can get another small business waiver, even if the original application was later withdrawn or refused.
There is no automatic small business waiver for the annual product and establishment fees that begin after approval, though small businesses can apply for those to be reduced or waived under separate public health barrier or innovation barrier provisions.15Food and Drug Administration. User Fee Waivers, Reductions, and Refunds for Drug and Biological Products
For technical help, the FDA’s CDER Small Business and Industry Assistance (SBIA) program runs workshops, publishes educational materials, and answers questions from sponsors preparing a first eCTD filing. SBIA can be reached at 866-405-5367 or CDERSBIA@fda.hhs.gov.16Food and Drug Administration. Small Business Assistance