My friend was prescribed zithromax for suspected chlamydia infection and he was then prescribed another gram when treatment failed. is this normal?

Hard to say: One of the primary reasons for treatment failure is the wrong diagnosis which led to ineffective treatment.You say "suspected"chlamydia".This agent shares symptoms with other germs, and retreating the wrong condition with an otherwise effective med is odd. I would want to confirm the diagnosis. Another possibility is continued exposure to an untreated partner with re-infection.