Table 1.

Measurements of QC samples, subdivided by antimicrobial drug and concentration level

Drug	Number of measurements	Concentration level	Measured concentration relative to true value (%)	Absolute inaccuracy (%)a	Measurements with acceptable accuracyb
					n	%	overall %
Ceftazidime	14	low	89 (69–160)	16 (4–60)	9	64	56
	11	high	85 (75–125)	20 (2–25)	5	45
Ciprofloxacin	4	low	98 (74–98)	2 (2–26)	3	75	82
	7	high	88 (78–106)	12 (6–22)	6	86
Flucloxacillin	10	low	96 (89–112)	7 (1–12)	10	100	100
	11	high	95 (80–101)	5 (1–20)	11	100
Piperacillin	8	low	105 (69–6250)	11 (1–6150)	5	63	75
	12	high	106 (89–121)	10 (2–21)	10	83
Tazobactam	3	low	107 (107–115)	7 (7–15)	3	100	88
	5	high	99 (82–125)	7 (0–25)	4	80
Sulfamethoxazole	10	low	96 (80–112)	7 (0–20)	9	90	94
	8	high	97 (91–100)	3 (0–9)	8	100
N-acetyl sulfamethoxazole	7	low	95 (86–114)	7 (0–14)	7	100	100
	6	high	96 (91–100)	4 (0–9)	6	100
Trimethoprim	7	low	97 (73–1453)	27 (3–1353)	2	29	62
	6	high	91 (87–92)	9 (8–13)	6	100

Data are presented as median (range) unless otherwise stated.

^aInaccuracy is the percentage bias from the true concentration., i.e. inaccuracy = (100 × measured concentration/true concentration) − 100%.

^bAcceptable measurements are within the 80%–120% limits of the true concentrations.