You are treating a 22 yr old female who complains of burning…

Yоu аre treаting а 22 yr оld female whо complains of burning with urination, frequency and urgency x 4 days.  Dipstick urinalysis shows: + Leukocytes,  + Nitrites     Trace Blood .  Urine Pregnancy Test  is Negative.  What is a  first line antibiotic choice and duration of treatment?