The overall potency estimate of the candidate standard 86/500 based on the laboratories performing bioassays is 211.3 IU, with 95% confidence interval from 189.4 to 235.7 IU. Samples A and B (86/500) and sample C (86/564) were all included in the original collaborative study that was conducted to establish the 1st IS 86/504 (Kirkwood,

1979). Based on the data presented in that study, the estimated potency of 86/500 relative to 86/504 was 204 IU, in excellent agreement with the results from the current study, and providing further evidence of the long-term stability of 86/500. The potency of 86/564 relative to 86/504 in the original study was 225 IU, in reasonable agreement with http://www.selleckchem.com/hydroxysteroid-dehydrogenase-hsd.html the results from the current study. The potency of sample C (86/564) was also calculated relative Crizotinib to sample A (86/500), the candidate

replacement IS, assuming a hypothetical value of 200 IU for 86/500. These calculations were performed for each assay, and the laboratory means, within-laboratory between-assay %GCVs, and overall means, were calculated in the same way as for potencies relative to 86/504 above. The individual laboratory mean estimates are shown in Table 8, along with the within laboratory %GCVs. The overall mean estimate, and between-laboratory %GCV, are also shown in Table 8. The overall mean is 235 IU, consistent with the overall mean of 236 IU calculated relative to 86/504 (Table 4). The between laboratory and within laboratory variation, as measured by the %GCVs, are comparable to the values obtained for sample C relative to 86/504. For this, samples of 86/500 stored at − 70 °C, − 20 °C, + 4 °C and + 20 °C were assayed, subsequently analysed and potencies either expressed relative to the samples stored at − 70 °C. The mean potency estimates

of the candidate A (coded 86/500) stored at different temperatures (expressed as a percentage of the − 70 °C sample) are shown in Table 9. There is no detectable degradation, even after 26 years at + 20 °C. It is not possible to apply the usual Arrhenius model to obtain predictions of % loss per year, as there is no degradation. Clearly 86/500 is very stable, and suitable to serve as a standard. Although samples had also been stored at + 37 °C, it was not possible to properly reconstitute these samples after such a long period at high temperature. Therefore, to confirm the stability at + 37 °C, an additional assay was performed on a sample that had been stored for 1 month at + 37 °C, and this was indistinguishable from the − 20 °C sample (data not shown). Further studies showed that the potency of 86/500 is not diminished after 1 week of storage at either + 4 °C or + 20 °C following reconstitution. However, it is recommended that 86/500 is used soon after reconstitution.