Table 3.
Necessary impurity level to cause 20% bias on Ki estimates from inhibition studies.
| Potency of Inhibitor | Ki/Kja | Necessary Xj level to cause bias in Ki |
|---|---|---|
| Most strong (Ki = 0.05 μM) | ≤ 0.1 | Never a concern when Xj ≤ 10% |
| Very strong (Ki = 0.5 μM) | ≤ 1 | Never a concern when Xj ≤ 10% |
| Strong (Ki = 5 μM) | ≤ 1 | Never a concern when Xj ≤ 10% |
| 10 | 2.5% | |
| Moderate (Ki = 50 μM) | ≤ 1 | Never a concern When Xj < 10% |
| 10 | ≥ 2.5% | |
| 100 | ≥ 0.6% | |
| Weak (Ki = 500 μM) | Eqn 4 (appendix B) did not adequately fit data. | |
a
Ki/Kj reflects the ratio of the “true” inhibition constant of the inhibitor of interest versus the inhibition constant of its impurity.