1. The eCTD
The Common Technical Document (CTD) describes the organisation of modules, sections and documents to be used for a MAA for a medicine, agreed by the ICH. The electronic Common Technical Document (eCTD) allows for the electronic submission of the CTD from applicant to regulator. While the table of content is consistent with the harmonised CTD, the eCTD also provides a harmonised technical solution to implementing the CTD electronically. The eCTD is not merely a collection of PDF documents, and the documents cannot be gathered into one huge PDF file either.
Both the company and the assessors must be able to easily navigate in the dossier. Therefore, the eCTD is a standard that describes in detail the folder and file structure. Within a complete eCTD dossier, navigation is possible like in a normal directory on a computer. In other words, an eCTD is a standardized interface for the submission of PDF documents, stored in the eCTD directory structure, accessed through the XML backbone and with file integrity guaranteed by the MD5 Checksum.
What is CheckSum?
A checksum is a string of numbers and letters used to uniquely identify a file. Checksum is most commonly used to verify if a copy of a file is identical to an original.
How does CheckSum work?
A file is pushed through an algorithm, which outputs a unique alphanumeric string called a checksum, also known as a "hash". Different files, even those with minute differences, produce different checksum values.
There are multiple algorithms that can be used to produce a checksum value. The algorithm used for eCTD submissions within EU to provide checksum values is MD5. The MD5 message-digest algorithm is a widely used hash function producing a 128-bit hash value.
What circumstances would warrant verifying a CheckSum value?
Files may be changed during download, transmission, or storage. For example, if there is an issue with network connectivity at the time of download, the file may not download correctly. Issues with hard drive storage could also lead to file alteration.
CheckSum can be used to verify any type of file.
The eCTD format is mandatory to use for all submissions (e.g., MAAs, variations, paediatric, referrals, renewals, etc.) related to Marketing Authorisation for products within all EU procedures (i.e., Centralised, Decentralised and Mutual Recognition Procedures) and new regulatory activities in National Procedures.
The current version of the eCTD specification to be used for CTD modules 2-5 is the Electronic Common Technical Document Specification V3.2.2 (PDF). More information about the standard can be found at the ICH eCTD webpage. For eCTD submissions within the EU, covering the regional module 1 of the CTD, the EU Module 1 eCTD Specification (April 2021) should be used.