Can metronidazole 500mg treat gonorrhea?

No. Metronidazole is not recommended for treatment of gonorrhea. The cdc has recommended certain cephalosporin antibiotics as gonorrhea is becoming more resistant to previously used drugs. See this link for more info: http://www.Cdc.Gov/nchhstp/newsroom/docs/gonorrhea-treatment-guidelines-factsheet.Pdf.