How long do 4 metronidazole 500mg tablets stay in your system?

8-10 hrs: The time for elimination from body, also related to its half life, for Metronidazole is estimated to be 8-10 hrs. Pl be conservative in your estimation if alcohol consumption is considered to avoid potential complication with this drug. Be safe:)

Metronidazole: Check out http://www.drugs.com/metronidazole.html where it states "Do not drink alcohol while you are taking metronidazole and for at least 3 days after you stop taking it." In general, it takes about 5 half-lives to get something out of your system, but this is just a starting point for estimation and varies depending upon metabolism, kidney & liver function, etc. Same reference say 8hr half-life