Single Dose Intravenous Antibiotics for Complicated Urinary Tract Infections in Children

Inclusion Criteria: * 3 months (corrected age) to 18 years * Fever (reported fever at home or measured fever of ≥38 degrees Celsius associated with the illness that triggered current ED presentation (eg fever may have been 18 hours prior to presentation but none since then because patient has been on maximal antipyretics - paracetamol or ibuprofen) * Any of the following complicating features: Vomiting, Rigors, History of recurrent UTI, Urological abnormalities, Tachycardia * Urine sample available (Urine culture must have been collected prior to or within an hour of antibiotic treatment, either at the GP or ED - in order to assess urine culture as per below). * Abnormal urinary dipstick leucocyte esterase \>1+ or nitrite positive OR ≥5 White Blood Cells (WBCs) per high-power field in centrifuged urine OR≥ 10 White Blood Cells (WBCs) per mm3 in uncentrifuged urine and bacteriuria with any bacteria per high-power field * ED clinician determines the child requires treatment with IV antibiotics \* In ED, only urine dipstick or urinalysis will be available. Once urine culture is available, to be included in the efficacy analysis, culture results must meet the following criteria: Positive urine culture result with no more than 2 species of microorganisms AND Spontaneously voided urine with ≥105 microorganisms per mL of urine or Suprapubic aspirate or urinary catheter with ≥104 microorganisms per mL of urine. In the absence of a positive urine culture, ultrasonographic findings supporting pyelonephritis (per reporting radiologist) will be accepted as evidence of a urinary tract infection. In the absence of a positive urine culture or supportive ultrasonographic findings, a case will also be accepted as presumed UTI where the treating clinician has provided a diagnosis of UTI and treated the patient accordingly. Exclusion Criteria: * Sepsis (requiring inotropic support or more than 20ml/kg of fluid bolus in Emergency Department) * Known allergy to all once daily study drug options (gentamicin or ceftriaxone or amikacin) * If the patient has another co-existing condition which requires (based on established evidence-based guidelines) more than 1 dose of IV antibiotics eg meningitis * Known chronic renal failure or renal transplant patients * Unrepaired posterior urethral valves * Indwelling stent and fever * Previously enrolled participants in the CHOICE UTI trial. * No available oral antibiotic option for this UTI: urine culture result already available and multi-resistant organism with susceptibility only to IV antibiotics or known intolerance to oral antibiotics (previous UTI with multi-resistant organism not an exclusion) * Previous IV antibiotics for same UTI episode eg interhospital transfer whereby significant time has passed since first dose IV * Patients with clinically suspected renal abscess e.g., extreme renal tenderness, out of keeping with pyelonephritis (clinically determined). * Clinician does not intend on prescribing a course of IV antibiotics but plans on only giving a single dose from the outset * Recurrence of urinary tract infection within 2 weeks * Unable to obtain consent * Patient is pregnant