Effect of cephalothin on measurement of creatinine concentration.

Cephalothin, an antibiotic implicated as nephrotoxic, falsely elevates the creatinine concentration as determined by the Jaffé reaction in vitro. We studied this effect in vivo and demonstrated variable degrees of interference in determinations of plasma and urinary creatinine concentrations by two automated methods. Clinicians should be aware of this phenomenon in patients receiving cephalothin, both when monitoring renal function and when assessing patient reliability in the collection of timed urine specimens.