Nizonide 500mg contains nitazoxanide, an antiparasitic and antiviral medication used to treat infections caused by protozoa, helminths, or viruses. It’s commonly prescribed for conditions like diarrhea caused by Giardia lamblia or Cryptosporidium parvum. Taken orally, it requires a doctor’s guidance. Side effects may include nausea, headache, or stomach pain.