I was given flagyl 250 to cure my ecoli infection. is that the right strength? i remember being given flagyl 500?

Wrong antibiotic: If you've been given Flagyl for an E. coli infection- that doesn't make proper sense, since it will not work against E. coli. I would call the doctor to ask 'what' they are actually treating and why. There are different doses of Flagyl (metronidazole) and 500 mg is a standard dose. Sometimes a doctor will dose adjust a medication depending on the patient and the infection. You need to get answers.