from wikipedia:
The use of sulfasalazine has declined due mainly to the fact that it yields the metabolite sulfapyridine which gives rise to side-effects such as agranulocytosis and hypospermia. However, the other metabolite of sulfasalazine, 5-aminosalicylic acid (5-ASA) is attributed to the drug's therapeutic effect. Therefore, 5-ASA and other derivatives of 5-ASA, are now usually preferred and given alone (as mesalazine), despite their increased cost, due to their more favourable side-effect profile.
Agranulocytosis, also known as agranulosis, is an acute condition involving a severe and dangerous leukopenia (lowered white blood cell count), most commonly of neutrophils, causing a neutropenia in the circulating blood. It represents a severe lack of one major class of infection-fighting white blood cells. People with this condition are at very high risk of serious infections due to their suppressed immune system.
Hypospermia is the medical term when a man has an unusually low ejaculate (or semen) volume
