I interviewed at Pfizer for a Principal SWE role last fall and the system design round surprised me. Sharing because most advice online is way too generic.
For context: I'm a director now but went through this loop because I was considering a move to healthcare tech. Role was in their Digital R&D org.
The prompt Design a system that tracks adverse event reports from clinical trial sites in real time and routes them to the appropriate regulatory reviewers based on severity and geography.
Not "design a URL shortener." That's the calibration right away.
What they looked for
The interviewer (a staff engineer from their platform team) wasn't looking for maximum throughput or a Kafka-everywhere answer. He kept pushing on: Data integrity guarantees. What happens when a report is submitted twice? What's the source of truth? How do you handle partial failures? Audit trails. Every state transition in a regulated system needs to be logged immutably. I drew out an event-sourcing pattern and they responded well to that. Human-in-the-loop workflows. Fully automated routing wasn't acceptable for high-severity events. Needed escalation paths and manual override mechanisms. Compliance at the edges. I mentioned GDPR and 21 CFR Part 11 (FDA electronic records). This landed well. If you don't know what Part 11 means, spend 20 minutes on it before your interview.
What didn't matter as much Exact choice of message queue (they run Azure and have opinions, but weren't grading on that). Micro-optimization of p99 latency. Auto-scaling specifics.
My advice for this round Frame every design decision around 'what's the cost of being wrong here?' In pharma, the cost is potentially patient harm or an FDA warning letter. That mental model will make your answers land.
The round was 75 minutes. First 10 were problem clarification, which they seemed to care about a lot. Don't skip that step.