Amoxicillin / clavulanate
"This medication made me seriously ill.  I was prescribed it following an animal bite that resulted in infection.  I took the first dose and two hours later I was stricken with violent projectile vomiting that caused me to lose control of my bladder and bowels.  I reported this to my doctor who was sure it wasn't the medication and advised that I try taking 1/2 the dose.  The second dose also cause side effects, and I had to go to urgent care with an iv. After 5 hours in urgent care and three bags of fluid and antibiotics with anti-nausea medicines I finally went home.  I've never vomited so violently ever."