More than 80% of incidents occur due to Escherichia coli (gram-negative rods).
Most strains of this pathogen are susceptible to many drugs, although antibiotic-resistant strains are quite common.
For the treatment of acute cystitis, it's common to apply single intake of trimethoprim/ sulfamethoxazole (320/1600mg), trimethoprim (400mg), sulfamethoxazole (2g) and most fluoroquinolones (norfloxacin, ciprofloxacin, ofloxacin).
This obstacle makes treating the condition with a single dose of Amoxicillin (3g.), very difficult.
About a third of Escherichia coli strains that lead to acute cystitis are resistant to amoxicillin.