Drixenol "Drix" Koldreliff is the boxy, red-and-yellow cold pill from the Osmosis Jones franchise. He is the by-the-book kind of cop that adheres strictly to the rules, unlike his newly-assigned partner, Osmosis Jones. He is clever, but doesn't really have a sense of humour.
David Hyde Pierce voices Drix in the live-action/animated feature film. Pierce's normal voice is a perfect match for Drix, conveying the almost-naivety to the truly disgusting nature of crime work inside the human body.
In the spin-off series, Jeff Bennett took over the role. Much like Phil LaMarr in the Ozzy compare, Jeff seems like a natural choice to replace David Hyde Pierce. It's not a perfect imitation, but it's good enough for a serialized portrayal of the character.
While Jeff Bennett is good in the role, my vote goes to David Hyde Pierce.