Genotoxicity
Naloxegol free base was evaluated in the standard genetic toxicology battery, including the bacterial
mutation (Ames) test, the mouse lymphoma TK assay and the mouse bone marrow micronucleus test.
Naloxegol free base was found to be positive in the Ames test. Naloxegol free base was negative in the
mouse lymphoma TK assay and the in vivo micronucleus assay. Naloxone has also been shown positive in
the Ames mutagenicity and in vitro human lymphocyte chromosome aberration tests but was also not
genotoxic in vivo. In addition, phenanthrene-based drugs, to which naloxegol and naloxone belong, as a
class do not seem to represent a carcinogenic risk to patients (Aardema et al, 2008). However, following
the identification of glycidaldehyde as a genotoxic degradation product in various batches of naloxegol
free base, naloxegol oxalate was selected for commercial formulation which avoids the formation of this
genotoxic degradation product. Naloxegol oxalate was negative in the Ames test. The amount of
glycidaldehyde that is still present as impurity has been measured to be below 10 ppm and is thus present
in amounts below the TTC, which is acceptable.