Zombie Doctor

Type: Rhodes Hill Care Center
Chapters: Chapter 2 (Leon): Rehabilitation Ward, 2 in the Main Office cutscene and 5 bursting out of the Storeroom with 1 Zombie Patient. Chapter 3 (Grace): Treatment Room (1), Connecting Corridor (3, red-lit; they walk at you), Conference Room (3, rise from the floor) and Parlor (1, rises after the ID Wristband (Level 1); on Insanity, as soon as you explore).

Weak point

The head. Chainsaw carriers take far more shots.

Tactic

Some carry a knife, a syringe (the nurse stabs), a big bonesaw (kills fast) or a chainsaw.

The chainsaw doctor (chapter 2): shoot him first and spend the Requiem here. A parry works but breaks the Hatchet: sharpen with L + Y while backing off. Wait for the dropped chainsaw to stop spinning before you pick it up, and kneecap zombies that go for it. Fall back to the raised area opposite the office.
Connecting Corridor (chapter 3): they walk in a line: a good spot for Bang for Your Buck with one Requiem round. You can also hide crouched behind the row of plants by the fireplace: the bonesaw surgeon walks on to the Treatment Room and the other two turn back.
As Grace, a Hemolytic Injector from behind kills them instantly.

Drops

Leon's Chainsaw (chapter 2; used up opening the door with the sliding bar). In chapter 3, a Med Injector in the Connecting Corridor, and a Hunting Knife and a Med Injector in the Conference Room.

Insanity: the Connecting Corridor bonesaw surgeon drops an Antique Coin instead of the Med Injector, and the Conference Room Med Injector is gone too.