Clindamycin
"I was prescribed this drug for an ear and sinus infection. Within an hour of the first dose, I got a bitter taste on my tongue. But not just on what you think as your tongue. I can also taste it halfway down my throat. It's so bad I have to constantly chew gum, eat, or drink something strongly flavored. It also keeps me awake at night. I have to keep gum in my mouth, which I press flat and smush to the roof of my mouth. 

After five days and four nights, I finally cried uncle and called my doctor, who told me to discontinue the medicine. Unfortunately, the taste persists, and I've now got burning pain in my esophagus. The good news is my ear/sinus infections are better, but clindamycin is going on my allergy list. I'll never take it again."