Ecstasy is often taken in tablet or pill form and is usually considered to be a hallucinogenic drug, often taken at parties or raves to enhance, music, lights and sounds. Many people take ecstasy, or 'E's as they are known, with alcohol or other drugs in order to enhance the impact of the drug, though this can be a dangerous procedure, as some drugs mixed together can cause harm and even create a lethal cocktail. Often people will unwittingly take ecstasy with prescribed drugs if they are on medicines for health issues and it is worth checking to see what the results are of mixing your drugs if you intend to.
Metronidazole is an antibiotic drug which is used for bacterial infections. Its side-effects are known to be nausea and flushing of the skin. When mixed with alcohol, these effects can be made more acute. As for mixing with Ecstasy, there is no evidence to show that doing so will cause any more harm than usual, though it is still not advised. It is more than likely that should you suffer any ill effects, it is down to the body attempting to digest the antibiotics and the recreational drugs at the same time.
It may be the case that mixing the two hampers the work of the antibiotics in fighting the infection. So it is best to wait until you have fully recovered from your illness and are no longer taking the antibiotics, before taking the ecstasy.