The Danish Medicines Agency (DKMA) is running a web page on FAQs on GMP where answers to frequently asked questions regarding Annex 13 on medicinal products in clinical trials in the European guidelines on GMP can be found.
One interesting Q&A is dealing with validation of critical manufacturing processes:
"In section 18(3) of the revised executive order on GMP/GDP (19 October 2004), it is indicated that all critical manufacturing processes must be validated. Must validation be conducted exactly as for medicinal products with a marketing authorisation or should the stage of development of the product be taken into consideration?"
"In paragraph 17 of Annex 13, it is indicated that validation is not expected to the same extent as for routine manufacturing of medicinal products. The term critical manufacturing processes in the executive order refers to particularly critical processes, such as those specifically mentioned in paragraph 17 of Annex 13, e.g. virus inactivation and sterilisation processes. Such particularly critical processes are expected to be validated for all medicinal products, even at the earliest stages of development of a product. The extent of additional validation is expected to increase with the product development, so that for medicinal products for stage III clinical trials, full validation is usually carried out so that it corresponds to the level of medicinal products with marketing authorisation. Incidentally, the formulation has been changed in the current executive order on GMP/GDP."