In January 2017, FDA issued the final guidance document, UCM429304, Current Good Manufacturing Practice Requirements for Combination Products.
The introduction says that this final guidance document describes and explains the final rule on combination products in 21 CFR Part 4. Prior to the final rule, there were regulations in place for the things that go into combination products, but no regulation to explain their application to the combination. This final guidance document provides additional information on applying the approach in Part 4.