There is a choice of 2 doses :-
Metronidazole, 2g orally, in a single dose or Metronidazole 400mg twice a day for 5 days. Both treatments are equally effective but while the single dose is more convenient you are more likely to suffer from side effects; the most common being diarrhoea, nausea and abdominal pain.
Preferably, you should take the tablet(s) during or after a meal and they should be swallowed whole, not chewed or broken, with water.
You are advised not to drink any alcohol while taking your antibiotics and for at least 48 hours after finishing treatment. This is because the alcohol may cause the antibiotics to give you a severe headache, make you feel sick or produce palpitations. However, the antibiotics would still work if you get this reaction.