An NCB (stockbroker) analyst has pulled together a nearly 30 page review of the pharmacology of Tysabri and concluded that Tysabri may have caused PML due to an underappreciated interaction with Avonex that lead to a build-up and eventual overdose of Tysabri. This idea was discussed here at This is MS long ago, given that clearance of Tysabri from the body in the presence of Avonex is sigificantly delayed. However, this document goes to great lengths to understand why this may lead to PML.
Dosing Avonex and Tysabri together "essentially leads to almost double the intended Tysabri concentration after only 20 weeks,'' NCB analyst Orla Hartford said. ``Patients on Tysabri alone did not accumulate the drug.''
"This suggests to us that over a sustained period of Tysabri and Avonex treatment, the trends of accumulation and reduced clearance of Tysabri lead to an `overdosing,'" she said.
This accumulation might have led to immuno-suppression in the brain, and likewise have been a key pre-disposing factor in the cases of PML seen in combination therapy, Hartford said.
She added that the effect Avonex has on Tysabri will "form a central part of the case made to the FDA for Tysabri's relaunch."
Note that two of the three confirmed PML cases were indeed Tysabri + Avonex patients, while the third patient was purportedly on Tysabri alone, but as a previous analysis here showed, he was actually on a cocktail of powerful immunosuppressants which at some point overlapped with the Tysabri dosing.
Please click "read more" to read a copy of the source study by NCB.
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(Unofficial site-- thanks to our members for finding this report, and the host for providing it)
