strep throat
"Took this for strep throat.  First day was okay (besides the fact that these pills are rather large and hard to swallow). Second day was horrible.  Diarrhea twice, then my heart started racing. Called the doctor who said go the emergency room right away this medicine can cause heart palpitations.  Heart rate was around 130 bpm for over 4 hours with no sign of slowing down. Finally the doctor in the ER decided to administer an anti-arrhythmic medicine to decrease the heart rate.  

The clarithromycin did seem to start working almost right away, after my second dose I felt much better, then the horrific side effects kicked in. "