Can amoxicillin (amoxicillin) cause a change in the smell of a child's urine?

Can Amoxicillin Cause Bad-Smelling Urine in Children?

Amoxicillin itself does not directly cause malodorous urine as a recognized adverse effect, but changes in urine odor during amoxicillin treatment should prompt evaluation for an underlying or secondary urinary tract infection.

Understanding the Relationship

The available evidence does not list malodorous urine as a documented adverse effect of amoxicillin in children. The most commonly reported adverse effects of amoxicillin and amoxicillin-clavulanate in pediatric patients are:

• Gastrointestinal disturbances (diarrhea, vomiting, abdominal pain) occurring in approximately 5% of patients, with rates as high as 44% for high-dose amoxicillin-clavulanate 1
• Dermatologic reactions (rash, dermatitis) 1
• Disruption of intestinal microbiome potentially contributing to long-term effects 1, 2

Clinical Significance of Malodorous Urine

When a child on amoxicillin develops foul-smelling urine, consider these possibilities:

Primary Concern: Urinary Tract Infection

• Malodorous urine is a classic symptom of UTI, not a medication side effect 1
• A case report documented Aerococcus urinae infection presenting specifically with malodorous urine in a 15-month-old child, which was successfully treated with amoxicillin 3
• The prevalence of UTI in febrile children under 2 years ranges from 3-7%, with higher rates in girls (6.5-8.1%) and uncircumcised boys 1

Clinical Algorithm for Evaluation

If a child on amoxicillin develops malodorous urine:

1. Obtain urinalysis and urine culture to rule out UTI, as foul-smelling urine may indicate bacterial infection rather than medication effect 1, 3

2. Assess for other UTI symptoms:

   • Fever (most common symptom in young infants) 1
   • Irritability, poor feeding, vomiting, or diarrhea 1
   • Crying during urination 1
   • Changes in voiding pattern 1

3. Consider the underlying condition being treated with amoxicillin, as the original infection or a secondary infection may be responsible 4

Important Caveats

• Renal toxicity from amoxicillin is extremely rare (0.03% incidence) and not dose-related, even with ingestions exceeding 250 mg/kg 5
• The absence of malodorous urine in documented adverse effect profiles from major pediatric guidelines suggests this is not a direct drug effect 1, 2
• Do not dismiss malodorous urine as a benign medication side effect—it warrants investigation for UTI, particularly in high-risk populations (young age, female sex, uncircumcised males, anatomic abnormalities) 1

Practical Management

The appropriate response is diagnostic evaluation, not reassurance that this is a normal medication effect. Obtain urine studies to identify treatable bacterial infections that may require adjustment of antibiotic therapy or completion of the current course if the organism is susceptible 3, 4.