How long does it take before z pack starts to work on tonsillitis?

2-3 days. If there is no improvement if 72 hours, you amy have a strain that is resistant to azithromycin. Rates of resistance to z pack are at least 40% here in the new york area. Let your doctor know if you still have severe pain or fever after 3-4 days. Keepin mind that the vast amount of tonsil infections are viral and will clear on their own in 7-10 days.