Protocol for the study of drug interferences in laboratory tests: cefotaxime interference in 24 clinical tests

We developed a protocol to study interference by cefotaxime and one of its major metabolites with 24 common chemical tests. Serum pools simulating specimens from healthy adults of both sexes, pregnant women, patients with liver disease, cardiac disease, or renal disease, and patients receiving gentamicin and tobramycin were supplemented with high and low concentrations of cefotaxime and desacetylcefotaxime. Using a discrete analyzer (the American Monitor Parallel), we tested 12 replicate samples from each condition for 24 analytes. Although statistically significant changes were found in many tests, 85% of the differences were less than 15% of the control value and more than half were less than 5%. The apparent concentration of creatinine was not significantly changed. Test results for phosphorus were increased in patients who were receiving gentamicin and tobramycin. No other changes were considered clinically significant.