Combination Products: How PMOA Determines the Lead FDA Center

A research team that combines a drug, device, or biologic component into a single product — a prefilled autoinjector, a drug-eluting stent, a biologic delivered through a proprietary device — doesn’t get to choose which FDA center reviews it. That choice is made by regulation, using a specific legal test called primary mode of action (PMOA). Getting the center assignment wrong, or not addressing it early, is one of the more common ways a combination-product development timeline slips by months: the wrong center means the wrong review pathway, the wrong set of applicable regulations, and often a restart.

This guide covers how FDA defines a combination product, how PMOA determines which center leads review, what happens when PMOA isn’t obvious, and how to use the Request for Designation (RFD) process to get a binding answer before you’ve committed to a development and submission strategy built around the wrong center.

What Counts as a “Combination Product”

FDA’s combination-product regulation, 21 CFR Part 3, defines a combination product at 21 CFR 3.2(e) as falling into one of four categories:

• A single entity in which two or more regulated components — drug/device, biologic/device, drug/biologic, or drug/device/biologic — are physically, chemically, or otherwise combined or mixed (a drug-eluting stent, a prefilled syringe with an integral delivery mechanism).
• Two or more separately packaged products, one a drug/device, device/biologic, or drug/biologic combination, packaged together (a diagnostic kit paired with a therapeutic).
• A drug, device, or biologic packaged separately that is intended for use only with an approved individually specified product, where both are required to achieve the intended use and approval would require a labeling change to the approved product.
• An investigational drug, device, or biologic packaged separately but intended for use only with another specified investigational product, where both are needed to achieve the intended use.

The unifying question isn’t packaging — it’s whether the components must work together to deliver the intended therapeutic or diagnostic effect. A team developing what looks like “just a device” (a wearable injector) or “just a drug” (a pre-loaded biologic cartridge) should check this definition early; combination-product status changes essentially everything downstream, including which office receives the application and which set of current Good Manufacturing Practice requirements apply (see CASRAI’s guide to GMP obligations that diverge from standard manufacturing practice for how this plays out for one adjacent product class).

Primary Mode of Action: The Test That Decides the Lead Center

Once a product is confirmed to be a combination product, FDA assigns it to a lead center — the Center for Drug Evaluation and Research (CDER), the Center for Devices and Radiological Health (CDRH), or the Center for Biologics Evaluation and Research (CBER) — using the PMOA. 21 CFR 3.2(m) defines PMOA as “the single mode of action of a combination product that provides the most important therapeutic action of the combination product,” where “most important therapeutic action” means the mode of action expected to make the greatest contribution to the product’s overall intended therapeutic effects.

In practice: if a drug-eluting stent’s clinical benefit comes primarily from the mechanical scaffolding restoring blood flow, with the drug coating reducing restenosis as a secondary contribution, the device mode of action is primary and CDRH leads. If the reverse is true — the therapeutic benefit is driven by the drug, with the device functioning mainly as a delivery mechanism — CDER leads, even though a device component is physically present. A biologic-device combination follows the same logic with CBER as the drug/biologic analog. This is a genuinely case-by-case determination; there is no universal rule that “if it contains a device, CDRH leads,” and sponsors routinely misjudge it based on which component looks more prominent rather than which one is doing the therapeutic work.

The Office of Combination Products (OCP), established under the FDA’s combination-products statute, is the body that makes and documents this assignment. OCP doesn’t review the product itself — the assigned lead center does that, consulting the other relevant center(s) as needed under an intercenter consultation/agreement — but OCP owns the jurisdictional decision and administers the RFD process described below.

When PMOA Isn’t Clear: the Fallback Algorithm

Many combination products have an obvious PMOA. Some genuinely don’t — a novel drug-device pairing with no close precedent, or one where the drug and device contributions are plausibly comparable. For those, 21 CFR 3.4(b) supplies a two-step fallback, applied in order:

1. Precedent first. FDA assigns the product to whichever agency component already regulates other combination products that raise similar safety and effectiveness questions for the product as a whole.
2. Expertise second. If no comparable combination product exists, FDA assigns it to the component with the most relevant expertise on the most significant safety and effectiveness questions the product presents.

This is exactly the situation an RFD is built to resolve — a sponsor facing genuine PMOA uncertainty shouldn’t guess at a center and build a development plan around the guess; the fallback algorithm is FDA’s own answer key, and the RFD is how a sponsor gets FDA to apply it to their specific product before, not after, major resourcing decisions.

The Request for Designation (RFD) Process

A Request for Designation, governed by 21 CFR 3.7 and 3.8, is the formal mechanism a sponsor uses to get a binding jurisdictional determination from OCP. FDA’s own guidance frames it as appropriate whenever a combination product isn’t already covered by an existing intercenter agreement, or when jurisdiction is otherwise unclear or in dispute — it is not a step every combination-product sponsor needs to take; well-precedented product types with an established center assignment generally don’t require one.

What the submission must contain

Per 21 CFR 3.7, an RFD is capped at 15 pages (original plus two copies) and must include:

• Sponsor identification: company name, address, FDA registration number, and contact details.
• A full product description: classification, proprietary and generic names, composition, manufacturing process, proposed indications/uses, mode(s) of action, dosage form and route of administration, and the regulatory status of related or predecessor products.
• The sponsor’s own recommendation as to which agency component should hold primary jurisdiction, reasoned from which mode of action is expected to provide the most important therapeutic action.

The submission is marked “Request for Designation” and filed with the product jurisdiction officer, with an electronic copy to OCP’s intake address.

FDA’s 60-day clock — and what a missed deadline means

Under 21 CFR 3.8, the product jurisdiction officer must issue a letter of designation within 60 days of the RFD’s filing date. This deadline has real teeth: if FDA fails to issue a designation within 60 days, the sponsor’s own recommended center automatically becomes the designated lead center. That default makes the sponsor’s stated recommendation in the RFD itself a strategically important input, not a formality — a poorly reasoned recommendation can end up governing the product by default if FDA simply doesn’t answer in time.

Disagreeing with the designation

A sponsor who disagrees with FDA’s designation has 15 days from receipt of the letter to file a written request for reconsideration, capped at 5 pages, with one binding constraint: no new information may be introduced in the reconsideration request — it has to argue from what was already in the original RFD. The product jurisdiction officer must respond within 15 days of receiving that request. There is no unlimited appeal cycle; sponsors get one narrow reconsideration shot, which is another reason the original RFD needs to be complete and well-argued the first time.

What This Means in Practice for a Research Team

For a team developing a combination product — whether inside an academic medical center’s spin-out, a sponsor-investigator IND/IDE program, or an industry partnership — the PMOA/lead-center question has consequences well beyond “who reviews the file”:

• It sets the applicable regulatory pathway. A CDER-led product generally follows an NDA/BLA-oriented review track (see CASRAI’s overview of the Investigational New Drug pathway); a CDRH-led product follows a device track — 510(k), De Novo, or PMA, chosen using the same predicate-device and substantial-equivalence logic that governs standalone devices, and often prepared using FDA’s eSTAR structured submission template.
• It determines which cGMP requirements apply. Combination products can trigger streamlined compliance with both drug/biologic cGMP (21 CFR 210/211 or 600s) and device Quality System Regulation requirements, depending on the assigned center and product type — a distinct question from, but structurally similar to, the divergent manufacturing requirements CASRAI documents for advanced therapy medicinal products.
• It affects premarket meeting strategy. Once jurisdiction is settled, the lead center’s own pre-submission mechanisms apply — for a device-led product, that generally means FDA’s Q-Submission program for early feedback.
• It shapes usability and human-factors expectations. Where a device or delivery mechanism is involved — even a drug-led product with a device component, like an autoinjector — FDA’s human factors and usability engineering guidance for combination products layers onto whichever center leads.
• It affects risk-management documentation. Device-relevant risk analysis under ISO 14971 is commonly expected for the device constituent of a combination product regardless of which center formally leads, since device-related failure modes don’t disappear just because CDER is the lead reviewer.
• Getting it wrong is expensive to unwind. A development program built around the assumption that a product is device-led, only to have OCP (or FDA at the point of submission) determine the drug mode of action is primary, can mean redoing nonclinical study design, manufacturing controls, and the submission format itself. Filing an RFD early — well before pivotal study design is locked — is materially cheaper than discovering the center assignment was wrong at the point of submission.

Teams unsure whether their product even qualifies as a combination product, as distinct from a standalone medical device, biologic, or drug, should resolve that threshold question first — the PMOA test and the RFD process only apply once combination-product status is established.

Frequently Asked Questions

Is filing a Request for Designation mandatory for every combination product?

No. An RFD is appropriate when a product isn’t already covered by an existing intercenter agreement or when jurisdiction is otherwise unclear or in dispute. Many combination-product types have well-established center assignments from precedent and don’t require a sponsor to file one — though a sponsor may still choose to file for certainty before committing to a development strategy.

Can FDA change the lead center after a product is already designated?

The RFD/letter-of-designation process under 21 CFR 3.7-3.8 is specifically designed to produce a determination sponsors can rely on for planning. The regulation provides the 15-day reconsideration mechanism as the process for a sponsor to challenge a designation it disagrees with — it is not a mechanism for FDA to unilaterally revisit a settled designation outside that window absent a materially different product.

What happens if FDA misses the 60-day deadline?

Under 21 CFR 3.8, if the product jurisdiction officer does not issue a letter of designation within 60 days of the RFD’s filing date, the center the sponsor recommended in the RFD is automatically designated. This makes the sponsor’s own recommendation and its supporting rationale a consequential part of the filing, not boilerplate.

Does the lead center review the product alone?

Not necessarily. The lead center owns the primary review, but FDA regularly uses intercenter consultation — the lead center can, and often does, consult the other relevant center(s) on specific questions (e.g., a CDER-led product with a device constituent consulting CDRH on device-specific safety questions) without changing which center holds overall jurisdiction.

Where does PMOA get evaluated relative to the rest of product development?

As early as possible. Nonclinical study design, manufacturing control strategy, quality system approach, and even which FDA meeting program to use (Q-Submission for device-led products versus the drug-oriented pre-IND process) all flow from the center assignment. Treating PMOA as a late-stage regulatory-affairs formality, rather than an early strategic input, is one of the more common avoidable causes of combination-product development delay.