10 Questions to Ask When Evaluating Custom API Manufacturing Partners

Generic CDMO rankings rarely tell you what you actually need to know. When your molecule involves complex chemistry, potent compounds or a compressed timeline to commercial launch, the questions that matter go deeper than capacity and certifications.

The right custom API manufacturing partner can accelerate your path to market, de-risk your supply chain and help you navigate regulatory complexity across global markets. The wrong one can cost you years.

Here are 10 questions that separate capable partners from capable-sounding ones.

1. What containment levels can you support—and how do you validate them?

For highly potent API (HPAPI) manufacturing, containment isn't a checkbox. It's a system. Ask specifically about Occupational Exposure Band (OEB) ratings. OEB5 capability—supporting compounds with occupational exposure limits below 0.1 µg/m³—requires purpose-built isolator systems, not retrofitted equipment.

A credible partner will explain their containment validation approach, not just claim a rating. At AbbVie Contract Manufacturing's HPAPI facilities, containment capabilities range from OEB3 through OEB5, with isolator-based charging and encapsulation systems designed for the most potent compounds.

2. How do you approach regulatory starting material selection?

Regulatory starting material (RSM) selection has downstream consequences for your control strategy, validation scope and global filing flexibility. A partner who treats RSM selection as a formality is a partner who hasn't navigated divergent regulatory expectations across FDA, EMA and other major markets.

Look for partners who apply ICH Q11 principles with a risk- and science-based framework—and who proactively identify backup RSMs in case agencies request alternatives. This kind of regulatory foresight can mean the difference between first-cycle approval and months of review delays.

3. What's your track record with tech transfer and scale-up?

Tech transfer is where many CDMO relationships fail. Ask for specifics: How many late-phase and commercial tech transfers has the site completed in the past five years? What's the typical timeline from transfer initiation to qualification batches?

Experience matters. AbbVie's Custom API operations have completed more than 20 late-phase and commercial tech transfers since 2012, with dedicated technical operations teams and labs at each site.

4. Can you support the full range of batch sizes my program may need?

Your API requirements will change as your program advances. A partner locked into a narrow batch-size range creates supply chain risk at exactly the wrong moment.

Ask about reactor scales across the network. Credible partners for API development services should support everything from gram-scale development through commercial batches of 600 kg or more—with flexibility to run multiple processes simultaneously.

5. How do you handle complex chemistries?

Not all custom drug synthesis is created equal. High-pressure hydrogenation, carbonylation, chromatographic purification and multi-stage processes each require specific equipment, expertise and safety protocols.

Ask which complex chemistry unit operations the site routinely performs—and which ones they've validated at commercial scale. A partner with genuine complex chemistry API capability will have specific examples, not generalities.

6. What's your approach to process validation and control strategy?

Process validation isn't just a regulatory requirement—it's a risk management tool. Ask how the partner defines critical quality attributes (CQAs) and critical process parameters (CPPs), and how they use scaled-down models and design of experiments (DOE) to establish process understanding before commercial-scale runs.

The best partners conduct pre-validation or demonstration batches with full controls in place before process performance qualification (PPQ). This approach catches problems before they become batch failures.

7. What analytical capabilities do you have on-site?

Analytical turnaround time directly affects your program timeline. Ask whether the site has on-site analytical laboratories for method development, validation, release testing and stability studies—or whether samples ship elsewhere.

Key capabilities to confirm: HPLC, UPLC, GC, residual solvents testing, heavy metals analysis and on-site microbiological laboratories. For HPAPI programs, confirm the lab can handle potent compound testing safely.

8. How do you manage impurity, fate and purge?

Mutagenic impurities, nitrosamines and other impurity risks require proactive management—not reactive firefighting. Ask how the partner conducts impurity fate-purge studies and whether they integrate this work into control strategy development from the start.

A mature partner will describe their approach to lab modeling, statistical analysis and FMEA-based risk assessments for impurity clearance. If they can't, you'll be managing that risk yourself.

9. What's your global regulatory footprint?

If you're filing in multiple markets, your API partner's regulatory track record matters. Ask how many countries have approved products manufactured at the site. Ask about recent inspection history with FDA, EMA and other major agencies.

Global pharmaceutical manufacturing experience also means understanding regional documentation requirements and anticipating where regulatory expectations diverge.

10. Can you support end-to-end supply from API through drug products?

For potent compounds especially, minimizing handoffs between API and drug product manufacturing reduces risk, simplifies logistics and shortens lead times. Ask whether the partner can support oral solid dose or other drug product manufacturing at the same site—or within an integrated network.

End-to-end capability from API through finished drug product can eliminate transportation and customs complexity while keeping your supply chain under tighter control.

The Bottom Line

Generic rankings can't tell you whether a CDMO partner will perform when your molecule is difficult, your timeline is compressed or your regulatory path crosses multiple markets. These 10 questions can.

The answers you get—and the specificity behind them—will tell you more about a partner's real capability than any marketing brochure.