bKanamycin is one of the aminoglycosides used in the treatment of multidrug-resistant tuberculosis. Blood concentrations of kanamycin are predictive for the treatment efficacy and the occurrence of side effects, and dose adjustments can be needed to optimize therapy. However, an immunoassay method for the quantification of kanamycin is not commercially available. We modified the existing tobramycin immunoassay to analyze kanamycin. This modified method was tested in a concentration range of 0.3 to 80.0 mg/liter for inaccuracy and imprecision. In addition, the analytical results of the immunoassay method were compared to those obtained by a liquid chromatography-tandem mass spectrometry (LC-MS/MS) analytical method using Passing and Bablok regression. Within-day imprecision varied from 2.3 to 13.3%, and between-day imprecision ranged from 0.0 to 11.3%. The inaccuracy ranged from ؊5.2 to 7.6%. No significant cross-reactivity with other antimicrobials and antiviral agents was observed. The results of the modified immunoassay method were comparable with the LC-MS/MS analytical outcome. This new immunoassay method enables laboratories to perform therapeutic drug monitoring of kanamycin without the need for complex and expensive LC-MS/MS equipment.T uberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis. Unfortunately, resistance to the two firstline drugs in TB treatment, isoniazid and rifampin, is emerging (1). Treatment regimens for multidrug-resistant TB (MDR-TB) include a quinolone and an injectable: amikacin, kanamycin, or capreomycin (2). Unfortunately, the use of aminoglycosides comes with toxic effects, such as renal failure and irreversible hearing loss (3).Recently, a study with MDR-TB patients showed that the toxicity of aminoglycosides was correlated with the cumulative area under the curve (4). For efficacy, it is well recognized that the top serum concentration (C max ) is related to the efficacy of aminoglycosides (5). In addition, pharmacokinetic (PK) guided dosing reduced the daily dose of aminoglycosides, with excellent treatment outcome (6). This indicates that serum concentration monitoring may be of added value in the treatment of tuberculosis. The targeted peak concentration for kanamycin in MDR-TB is 20 to 30 mg/liter (7), while the trough concentration should be as low as reasonably achievable in order to prevent toxicity.Although analytical methods to quantify the serum or plasma concentrations of amikacin and kanamycin using liquid chromatography-tandem mass spectrometry (LC-MS/MS) (8-11) have been described, this technique is commonly not available in most developing countries (12). However, in contrast to the case for amikacin, no analytical immunoassay kit to analyze kanamycin is commercially available.Kanamycin is more structurally related to tobramycin than to amikacin (Fig. 1). The product insert of the tobramycin immunoassay kit, based on the enzyme multiplied immunoassay technique (EMIT), indicates cross-reactivity for kanamycin (13). We therefore explored the...