In different studies, it has been shown that "antioxidant" utilization has favorable therapeutic effects not only on control of acute symptoms but also on prevention of delayed problems from acute and chronic pyelonephritis.

According to the efficacy of acetylcysteine as a potent antioxidant, safety of this drug and side effects of similar or either less than placebo, this study was designed to evaluate the efficacy of this drug on inflammatory biomarkers of pediatric acute pyelonephritis. It is a triple-blind placebo controlled study on a population of 64 patients 1-16 years old that have "definite" or "probable" diagnosis of acute pyelonephritis in "Mofid" hospital.

After randomization, patients will be given acetylcysteine or placebo with dosing according to their weight. Results of treatment are evaluated according to serum procalcitonin, C reactive protein and leukocyte count before drug prescription (baseline) and 5 days after drug prescription. Side effects are also recorded in both groups. Patients will be receiving their routine antimicrobial drugs in addition to acetylcysteine.

Inclusion Criteria:

• Patients between the ages of 1 and 16
• Having the diagnosis of "definite" or "probable" urinary tract infection according to guidelines of "pediatric infectious disease research center

Exclusion Criteria:

• Patients younger than 1 or older than 16 years old
• Patients without the diagnosis of "definite" or "probable" urinary tract infection according to guidelines of "pediatric infectious disease research center"
• Patients with acute/ chronic infectious or inflammatory diseases other than pyelonephritis.