Metronidazole? It's for giardia infections as well as hemorrhagic gastroenteritis.

Uromastyx generally are wild-caught and are wrought with internal parasites. If he hasn't had a full fecal test done on the uro, I would get one done to be safe. Could easily have more than giardia in his system. Giardia infections come from dirty water sources and is common in wild-caught animals.

Make sure he has a nice hot basking spot, keep him hydrated and give the meds. And definitely keep an eye on the bowel movements.