Combination product sponsors spend real time on which FDA center gets primary jurisdiction — the primary mode of action, or PMOA, determination. Far fewer spend the same care on a separate question 21 CFR Part 4 actually leaves open: which CGMP system governs manufacturing, and whether it has to be the same one PMOA assigned. It does not, and treating the two decisions as one is where quality systems quietly drift out of compliance.
What Part 4 actually offers
The 2013 final rule that created 21 CFR Part 4 was written to avoid forcing sponsors into redundant, duplicated quality systems. Subpart A gives a manufacturer two ways to demonstrate CGMP compliance: full dual compliance, independently meeting the drug CGMPs at 21 CFR Parts 210 and 211 and the device quality system requirements at 21 CFR Part 820 in their entirety, or a streamlined approach built around one system as the base, supplemented with the specific provisions FDA carried over from the other. FDA's 2017 guidance on the rule walks through how the supplemental provisions apply; the rule itself does not walk sponsors through how to choose a base.
The base doesn't follow the PMOA
PMOA determines which FDA center leads review — drug, device, or biologic. It answers a jurisdictional question. The CGMP base a manufacturer selects under the streamlined approach answers an operational one: which quality system does the bulk of the compliance work, and which specific provisions of the other framework get layered on top. Nothing in Part 4 requires the two answers to match, and in practice they frequently don't. A device-led CGMP base under a drug-PMOA product is common where the device constituent drives the bulk of manufacturing complexity; the reverse holds for a device-PMOA product manufactured primarily under a mature drug quality system.
- Where your manufacturing complexity actually sits. A base built around the constituent with the more demanding, more mature manufacturing process reduces the supplemental work rather than duplicating it.
- Facility and quality-system maturity. A site already running a robust device quality system under the QMSR may extend more efficiently to a drug constituent than the reverse.
- Contract manufacturing structure. When constituents are made at different sites under different systems, a two-systems approach run in parallel can be more defensible than forcing a single base across facilities that were never unified.
- Your existing regulatory relationships. A base tied to the framework your team already inspects and audits against carries less operational risk than adopting one from a center you rarely interact with.
Primary mode of action tells FDA who reviews the file. It says nothing about who runs the quality system that manufactures the product. Why the two decisions separate
What the supplemental provisions actually require
The streamlined approach is not a waiver of the non-base framework — it is a substitution of most of it for a defined list of provisions FDA judged essential regardless of which system is primary. A drug-based streamlined system still has to incorporate specific device-side controls: design controls, purchasing controls, corrective and preventive action, and acceptance activities among them. A device-based streamlined system still has to incorporate specific drug-side controls: stability testing, laboratory controls, and expiration dating among them. Treating the streamlined approach as 'mostly my base system, plus a checklist' undersells how substantive those carried-over provisions are; they are not filed away in a separate binder, they are supposed to be built into the operating quality system.
- Separate the two decisions explicitly. Confirm your PMOA determination and your CGMP base choice are documented as two distinct decisions, not one inferred from the other.
- Choose the base on operational grounds. Manufacturing complexity, facility maturity, and contract structure — not which center reviews your submission.
- Build the 4.4(b) provisions into the QMS. Don't leave them as a policy citation; wire them into procedures the way the rest of your base system already works.
- Write the rationale down before FDA asks. A one-page decision record showing approach, base, and supplemental provisions turns an inspection question into a five-minute answer.
None of this is exotic once it's named. It is a documented decision, a mapped set of supplemental provisions, and a quality system built to carry both — not two systems bolted together after the fact. Sponsors who treat the PMOA letter as the end of the jurisdictional homework are the ones who discover, usually at inspection, that nobody ever formally chose a CGMP base at all. If your combination product quality strategy hasn't separated these two decisions yet, that is where to start; it is a bounded piece of work under your quality-system implementation program, not a redesign.
Frequently asked questions
What is the difference between the streamlined and two-systems approach under 21 CFR Part 4?
The two-systems approach means fully implementing both the drug CGMPs (21 CFR Parts 210 and 211) and the device quality system requirements in their entirety, run as parallel systems. The streamlined approach lets a manufacturer operate under a single base system — drug or device — supplemented with the specific provisions the other framework requires under 21 CFR 4.4(b), rather than duplicating both in full.
Does the CGMP base have to match the center that reviews my combination product?
No. The FDA center with primary jurisdiction is determined by primary mode of action under the combination product jurisdiction process; the CGMP base a manufacturer selects under Part 4 is a separate operational choice. A device-led CGMP base under a drug-PMOA product is permitted, and the reverse is equally permitted, provided the choice is documented and the required supplemental provisions are in place.
What happens if a manufacturer doesn't formally choose either approach?
FDA's expectation is that a combination product manufacturer's quality system demonstrably satisfies Part 4 — either through full dual compliance or a documented streamlined approach. Without a documented rationale, an inspector has no basis to confirm which supplemental provisions apply, which is itself an exposure; treat the choice, and its documentation, as a decision made before manufacturing begins, not an after-the-fact label.
Sources & further reading
- FDA. Current Good Manufacturing Practice Requirements for Combination Products — Final Rule (78 FR 4307, Jan. 22, 2013). federalregister.gov
- FDA. Current Good Manufacturing Practice Requirements for Combination Products — Guidance for Industry and FDA Staff (Jan. 2017). fda.gov
- eCFR. 21 CFR Part 4 — Regulation of Combination Products. ecfr.gov
This article is provided for general informational purposes and reflects the regulatory landscape as of September 2026. It is not legal or regulatory advice. Confirm current 21 CFR Part 4 requirements with FDA or qualified counsel before acting.
