Metronidazole is a nitroimidazole derivative, which is rapidly and completely absorbed orally. Adverse reactions occur in 15%-30% of cases, with gastrointestinal reactions being the most common, including nausea, vomiting, loss of appetite, abdominal cramps, which generally do not affect treatment; neurological symptoms include headache, dizziness, occasionally abnormal sensation, numbness of limbs, ataxia, polyneuritis, etc. High doses may cause convulsions. In a few cases, urticaria, flushing, pruritus, cystitis, dyspareunia, metallic taste in the mouth and leukopenia occurred, all of which are reversible and recover on their own after discontinuation of the drug. Serious adverse reactions include toxic epidermal necrolysis relaxation, leukopenia, aseptic meningitis, encephalopathy, peripheral neuropathy, convulsions, optic nerve disorder, ototoxicity, and hemolytic uremic syndrome. Contraindicated in those with active CNS disorders and hematologic disorders. Pregnancy classification B. Avoid use during lactation. In mice and rats, metronidazole has been found to be carcinogenic and unnecessary use should be avoided. Alcohol should be avoided during and within three days of treatment with metronidazole.