The Neighbor (1993)

Ending / spoiler

Myron suffocated his baby brother because he blamed his offspring for causing his mother's death. Myron kills the nosy family dog, Poison's John's (the husband) boss and stabs/impales Mary(the pregnant wife)'s physician who's treating her (using some sort of a surgical tool). Mary fails to kill Myron by knocking him down some stairs, so she runs him through with a giant surgical syringe of sorts continueously till he dies.