TABLE 6.
Stability of QC samples stored under different conditionsa
| Antibiotic and nominal concn (mg/liter) | Stability of QC samples stored at −80°C for over 2 mo (n = 3) |
Stability of QC samples after 3 freeze-thaw cycles (n = 3) |
Stability of QC samples stored at room temp for 6 h (n = 3) |
Stability of QC sample extracts stored at +4°C for 72 h (n = 3) |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Mean measured concn ± SD (mg/liter) | CV (%) | Bias (%) | Mean measured concn ± SD (mg/liter) | CV (%) | Bias (%) | Mean measured concn ± SD (mg/liter) | CV (%) | Bias (%) | Mean measured concn ± SD (mg/liter) | CV (%) | Bias (%) | |
| AMX | ||||||||||||
| 6 | 6.42 ± 0.08 | 1.2 | 7.1 | 6.38 ± 0.21 | 3.4 | 6.4 | 6.28 ± 0.11 | 1.7 | 4.7 | 5.52 ± 0.06 | 1.2 | −8.1 |
| 30 | 32.05 ± 0.66 | 2.1 | 6.8 | 34.39 ± 0.52 | 1.5 | 14.6 | 32.33 ± 0.54 | 1.7 | 7.8 | 28.77 ± 1.09 | 3.8 | −4.1 |
| 70 | 73.18 ± 1.04 | 1.4 | 4.5 | 79.11 ± 1.20 | 1.5 | 13.0 | 72.22 ± 4.13 | 5.7 | 3.2 | 67.98 ± 3.23 | 4.8 | −2.9 |
| PIP | ||||||||||||
| 6 | 5.96 ± 0.03 | 0.5 | −0.6 | 6.33 ± 0.14 | 2.2 | 5.4 | 6.02 ± 0.33 | 5.5 | 0.3 | 6.23 ± 0.09 | 1.5 | 3.8 |
| 30 | 29.15 ± 0.72 | 2.5 | −2.8 | 31.25 ± 3.78 | 12.1 | 4.2 | 30.62 ± 0.48 | 1.6 | 2.1 | 30.13 ± 0.94 | 3.1 | 0.4 |
| 70 | 72.34 ± 2.18 | 3.0 | 3.3 | 76.14 ± 4.06 | 5.3 | 8.8 | 71.42 ± 3.24 | 4.5 | 2.0 | 60.61 ± 2.69 | 4.4 | −13.4 |
| OXA | ||||||||||||
| 6 | 6.21 ± 0.21 | 3.4 | 3.4 | 6.51 ± 0.18 | 2.7 | 8.6 | 6.19 ± 0.27 | 4.4 | 3.1 | 5.52 ± 0.07 | 1.3 | −8.1 |
| 30 | 30.17 ± 0.51 | 1.7 | 0.6 | 33.71 ± 0.74 | 2.2 | 12.4 | 31.24 ± 0.56 | 1.8 | 4.1 | 27.02 ± 1.03 | 3.8 | −9.9 |
| 70 | 66.56 ± 1.13 | 1.7 | −4.9 | 77.66 ± 0.22 | 0.3 | 10.9 | 71.38 ± 3.34 | 4.7 | 2.0 | 67.75 ± 4.63 | 6.8 | −13.4 |
| CLX | ||||||||||||
| 6 | 6.20 ± 0.85 | 13.8 | 3.3 | 6.00 ± 0.39 | 6.6 | −0.1 | 6.40 ± 0.07 | 1.1 | 6.7 | 5.68 ± 0.06 | 1.1 | −5.4 |
| 30 | 31.81 ± 0.26 | 0.8 | 6.0 | 33.35 ± 0.57 | 1.7 | 11.2 | 30.62 ± 0.53 | 1.7 | 2.1 | 27.70 ± 1.05 | 3.8 | −7.7 |
| 70 | 70.0 ± 1.28 | 1.8 | 0.0 | 77.13 ± 0.11 | 0.1 | 10.2 | 70.19 ± 3.31 | 4.7 | 0.3 | 62.58 ± 2.86 | 4.6 | −10.6 |
| FEP | ||||||||||||
| 6 | 6.06 ± 0.05 | 0.8 | 1.1 | 6.28 ± 0.14 | 2.2 | 4.7 | 5.92 ± 0.01 | 0.1 | −1.4 | 6.09 ± 0.11 | 1.8 | 1.6 |
| 30 | 30.74 ± 0.55 | 1.8 | 2.5 | 32.61 ± 0.40 | 1.2 | 8.7 | 30.16 ± 0.46 | 1.5 | 0.5 | 30.32 ± 0.93 | 3.1 | 1.1 |
| 70 | 74.48 ± 1.95 | 2.6 | 6.4 | 75.55 ± 0.53 | 0.7 | 7.9 | 67.92 ± 3.22 | 4.7 | −3.0 | 69.34 ± 2.85 | 4.1 | −0.9 |
| CAZ | ||||||||||||
| 6 | 6.03 ± 0.05 | 0.8 | 0.4 | 6.48 ± 0.10 | 1.6 | 8.1 | 6.12 ± 0.02 | 0.3 | 2.1 | 5.95 ± 0.10 | 1.7 | −0.9 |
| 30 | 30.30 ± 0.26 | 0.8 | 1.0 | 33.98 ± 0.32 | 0.9 | 13.3 | 31.54 ± 0.57 | 1.8 | 5.1 | 33.67 ± 1.58 | 4.7 | 10.4 |
| 70 | 72.72 ± 1.70 | 2.3 | 3.9 | 77.64 ± 0.56 | 0.7 | 10.9 | 70.74 ± 4.27 | 6.0 | 1.1 | 68.52 ± 2.89 | 4.2 | −2.1 |
| CTX | ||||||||||||
| 6 | 5.91 ± 0.05 | 0.9 | −1.6 | 6.47 ± 0.16 | 2.4 | 7.8 | 6.14 ± 0.01 | 0.2 | 2.3 | 6.04 ± 0.09 | 1.5 | 0.7 |
| 30 | 29.96 ± 0.27 | 0.9 | −0.1 | 33.17 ± 0.39 | 1.2 | 10.6 | 30.98 ± 0.44 | 1.4 | 3.3 | 29.80 ± 0.91 | 3.1 | −0.7 |
| 70 | 66.43 ± 0.63 | 0.9 | −5.1 | 77.16 ± 0.81 | 1.1 | 10.2 | 71.52 ± 3.33 | 4.7 | 2.0 | 69.01 ± 2.86 | 4.1 | −1.4 |
| CFZ | ||||||||||||
| 6 | 6.42 ± 0.06 | 0.9 | 6.9 | 6.63 ± 0.13 | 2.0 | 10.5 | 6.24 ± 0.01 | 0.1 | 3.9 | 6.39 ± 0.09 | 1.4 | 6.5 |
| 30 | 32.34 ± 0.38 | 1.2 | 7.8 | 34.10 ± 0.34 | 1.0 | 13.7 | 32.34 ± 0.48 | 1.5 | 7.8 | 30.65 ± 0.90 | 2.9 | 2.2 |
| 70 | 71.24 ± 0.62 | 0.9 | 1.8 | 79.76 ± 0.77 | 1.0 | 13.9 | 73.70 ± 3.36 | 4.6 | 5.3 | 69.67 ± 2.91 | 4.2 | −0.5 |
a
n, number of replicates; CV, coefficient of variation; AMX, amoxicillin; PIP, piperacillin; OXA, oxacillin; CLX, cloxacillin; FEP, cefepime; CAZ, ceftazidime; CTX, cefotaxime; CFZ, cefazolin.