Error in recovery rate of aminoglycosides from uraemic sera

The recovery rate of gentamicin and tobramycin from uraemic sera was between 50 and 70% using a bioassay method which gave a 90% recovery rate from normal sera. This difference was not seen with streptomycin or kanamycin. The recovery rate from uraemic sera could be raised to clinically acceptable levels of above 80% either by using a different assay medium or by preparing standard solutions in pooled uraemic sera.