Why does cefdinir (Cefdinir) cause red urine?

Why Cefdinir Causes Red Urine

Cefdinir causes red urine due to the formation of a nonabsorbable complex between cefdinir or its breakdown products and iron in the gastrointestinal tract, which is then excreted in the stool and sometimes affects urine color. 1

Mechanism of Red Urine Formation

• Cefdinir can bind with iron-containing products to form a reddish, nonabsorbable complex that is primarily excreted in the stool but can also affect urine color 1
• This interaction occurs specifically when cefdinir is administered concurrently with iron supplements, multivitamins containing iron, or iron-fortified foods 1, 2
• The FDA drug label specifically acknowledges this phenomenon, noting "there have been reports of reddish stools in patients receiving cefdinir" 1

Clinical Significance and Patient Education

• The red discoloration is benign and does not indicate gastrointestinal bleeding or other pathology 2
• The color change typically resolves within 48 hours after discontinuation of cefdinir 2
• This phenomenon is most commonly observed in infants and children who are receiving iron-fortified formula or supplements while taking cefdinir 2

Preventing Iron-Cefdinir Interactions

• To minimize this interaction, cefdinir should be taken at least 2 hours before or after iron supplements or multivitamins containing iron 1
• Iron-fortified infant formula does not significantly interfere with the absorption of cefdinir, so cefdinir suspension can be administered with iron-fortified infant formula without timing separation 1

Differential Diagnosis of Medication-Induced Urine Discoloration

• Other medications can also cause urine discoloration, such as metronidazole (which can cause dark or cola-colored urine) 3
• Cefiderocol, another cephalosporin antibiotic, has been reported to cause purplish urine discoloration 4
• When evaluating red urine in a patient taking cefdinir, clinicians should rule out other causes such as hematuria, hemolysis, or rhabdomyolysis 4, 2

Clinical Implications

• Healthcare providers should inform patients about this potential benign side effect to prevent unnecessary alarm and costly medical evaluations for suspected gastrointestinal bleeding 2
• The red discoloration does not affect the antimicrobial efficacy of cefdinir, which remains an effective treatment for respiratory and skin infections 5
• This side effect is not listed in the adverse drug reaction section of the cefdinir product labeling but is mentioned in the drug-drug interaction section, which may lead to it being overlooked during adverse event evaluations 2

Monitoring Recommendations

• No specific monitoring is required for this benign discoloration 1, 2
• If red urine persists beyond 48 hours after cefdinir discontinuation, further evaluation may be warranted to rule out other causes 2
• Patients should be reassured that this discoloration has no clinically relevant adverse outcomes 2, 3