Читать книгу Mutagenic Impurities - Группа авторов - Страница 138

1 1 The maximum observed PMI level can be designated by several means. These include: (i) by the amount of PMI introduced to the process, (ii) by the amount of PMI measured at a specific stage in the process, (iii) the amount in the process or by a level allowed by an acceptance criterion such as an assay value in an intermediate, or (iv) a hypothetical amount formed; this final approach is typically used where a PMI is formed by a side reaction.

2 2 ADIs are based on linear extrapolation of carcinogenicity data; PDEs are used where there is a definable threshold or no‐adverse effect level (NOEL).

3 3 In the case of a marketed product, this may be based on median duration for the class/disease area.

4 4 Should it be discovered that the level of an MI is above permitted levels in material currently used in clinical trials, then this may lead to suspension of the trial and expedited reporting under 15‐day rules to regulatory authorities.

5 5 While chloroacetyl chloride and its hydrolysis product chloroacetic acid contain structural features that alert for mutagenicity, both have been found to be nonmutagenic in the Ames test: American Conference of Governmental Industrial Hygienists. (1991). Documentation of the Threshold Limit Values and Biological Exposure Indices, Cincinnati, Ohio, 6e. ACGIH, p. 269. European Chemicals Agency, http://echa.europa.eu/ CAS RN 79‐11‐8, https://echa.europa.eu/registration‐dossier/‐/registered‐dossier/15187/7/7/2.Toluene and denatured ethanol are used within the process to manufacture GW641587X, and these solvents can contain low levels of the known carcinogen benzene. While benzene has an ADI of 20 μg/day, this solvent would need to be controlled to 2 μg/g within GW641597X as per ICH Q3C expectations (ICH guideline Q3C (R6) on impurities: guideline for residual solvents). Typical specifications of benzene in toluene and denatured ethanol are not greater than (NGT) 50–100 and 2 μg/g, respectively (in‐house experience). Toluene is used three isolated stages away from GW641597X, and levels of >0.5% solvent (ethanol/methanol) within GW641597X were achieved through drying (drier off‐load condition). It is reasonable to anticipate that residual levels of benzene would be purged to significantly below 2 μg/g in drug substance, and this would be confirmed at later phases of development through appropriate testing.

6 6 Excess reagents are generally only used to maximize yield for the certain processes because the reagent is otherwise being reduced either through undesired side reactions or through physical processes. If where large excesses are used, it is acknowledged for a high yielding reaction that 1 equivalent of reagent can be assumed to have reacted to form product that leaves the excess reagent requiring assessment.

7 7 Compound 4 is an oil and was isolated by evaporation, and therefore no solubility score can be assigned for residual alkyl bromide 2.

8 8 Monofunctional alkyl chloride can be controlled to 10 times the default LTL daily intakes according to Note 5 of ICH M7.

9 9 The reaction for deacetylation of acetate 4 proceeds to at least 98% completion, and the subsequent reaction of the intermediate phenolate with 8 to prepare 9 also proceeds to at least 98% conversion. This means that in principle there could be up to 4% of phenolate unavailable for reaction, meaning that an additional 0.04 equivalents of 8 could remain. The authors considered this a negligible difference to their assumption that up to 0.15 molar equivalents would remain, but it is acknowledged that a more accurate representation would be to consider 0.19 molar equivalents for the purge calculations.

10 10 The boiling point for ethyl bromoisobutyrate is >160 °C.

11 11 Weight ratio calculated by converting from the molar ratio with the molecular weights for alkyl chloride 8 (250.73) and GW641597X (424.50).

12 12 The purge prediction for Stage 4a and 4b would indicate that 15 mol% excess of alkyl chloride 8 should reduce to 0.15% m/m.