Sulphadiazine 500mg tablet works by stopping the growth of bacteria. It may be taken with or without food. You should take it regularly at evenly spaced intervals as per the schedule prescribed by your doctor. Taking it at the same time every day will help you to remember to take it. The dose will depend on what you are being treated for, but you should always complete a full course of this antibiotic as prescribed by your doctor. Do not stop taking it until you have finished, even when you feel better. If you stop taking it early, some bacteria may survive and the infection may come back.