TABLE 1

Measurements of quality control samples, subdivided by drug hand concentration level

DrugMeasurements nConc.#Measured conc. relative to true value %Absolute inaccuracy %Measurements with acceptable accuracy+
n%
Isoniazid7Low95 (84–105)5 (3–16)7100
7Int./high104 (80–108)7 (3–20)7
Rifampicin6Low78 (38–116)26 (6–62)342
6Int./high87 (49–135)27 (1–51)2
Pyrazinamide5Low108 (104–117)8 (4–17)5100
5Int./high110 (101–118)10 (1–18)5
Ethambutol6Low107 (75–137)14 (4–37)475
6Int./high104 (98–142)4 (1–42)5
Moxifloxacin3Low98 (95–108)5 (2–8)3100
3Int./high105 (87–106)6 (5–13)3
Linezolid2LowMean 95 (range 90–99)5 (1–10)2100
2Int./highMean 94 (range 89–98)6 (2–11)2
  • Data are presented as median (range) unless otherwise stated. Conc.: concentration; int.: intermediate. #: low and int./high conc. levels were 0.48 and 6.47 mg·L−1 (isoniazid), 1.41 and 5.60 mg·L−1 (rifampicin), 18.79 and 58.61 mg·L−1 (pyrazinamide), 0.93 and 4.78 mg·L−1 (ethambutol), 0.31 and 2.65 mg·L−1 (moxifloxacin), and 0.91 and 11.09 mg·L−1 (linezolid). : inaccuracy is the percentage bias from the true conc., i.e. inaccuracy = (100 × measured conc./true conc.)  − 100%. +: acceptable measurements are within 20% of the true conc.