Here's the latest: https://www.accessdata.fda.gov/drugsatfda_docs/label/2021/02...
> 12.3 Pharmacokinetics
> Metabolism Lisdexamfetamine is converted to dextroamphetamine and l-lysine primarily in blood due to the hydrolytic activity of red blood cells after oral administration of lisdexamfetamine dimesylate. In vitro data demonstrated that red blood cells have a high capacity for metabolism of lisdexamfetamine; substantial hydrolysis occurred even at low hematocrit levels (33% of normal). Lisdexamfetamine is not metabolized by cytochrome P450 enzymes.
EDIT: A better one: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4257105/
Basically, RBCs have lots of enzyme systems that serve (in part) to protect the important parts (e.g. haemoglobin) from oxidation. Put a bunch of lisdexamfetamine in the blood, and the RBCs will gradually hydrolyze it to cleave off the l-lysine and leave d-amph.
Do you have any more information about this? Can't find it on google - would be very interesting if its true but I'm a bit skeptical - I've never heard about blood cells being a primary site of drug metabolism.
A search turned up:
> "Lisdexamfetamine dimesylate is converted to dextoamphetamine and L- lysine, which is believed to occur by first-pass intestinal and/or hepatic metabolism."
(https://www.accessdata.fda.gov/drugsatfda_docs/label/2007/02...)
According to this, sounds like its mostly intestines and liver, which is much more typical for drug metabolisms.