nitrofurantoin: derivative of nitrofuran used as an antibacterial medicine (trade name Macrodantin) effective against a broad range of Gram-positive and Gram-negative bacteria; used to treat infections of the urinary tract
antibacterial: any drug that destroys bacteria or inhibits their growth
lacrimal sac: either of the two dilated ends of the lacrimal ducts at the nasal ends of the eyes that fill with tears secreted by the lacrimal glands