Monday, August 10, 2015

Up-Date on Platelets and Infusion #22 of Kadcyla/TDM-1 

Two weeks ago was a very good day for me. My platelets were 88,000/mmᶾ of blood which means they had improved enough for me to be treated. The dose remained reduced in hopes that my platelets will remain above 75,000.

The nurse practitioner and I discussed my current treatment plan with regard to my drop in platelets. She decided that I was being treated rather conservatively and according to the drug’s package insert I could be treated even when my platelets are close to 50,000/mmᶾ. So, 50,000 is my new targeted number. I will be back on my every three week schedule as long as my platelets don't dip below this number.

Though I did not verbalize the question, my NP answered a question that has been sitting in my brain for a while. “If TDM-1/Kadcyla is a targeted therapy then why are my platelets affected?” Kadcyla is ado-trastuzumab emtansine. Trastuzumab is Herceptin. It targets the Her 2 neu protein on the outside of my tumor cells. Emtansine or DM1 is a powerful chemical attached to the Herceptin molecule.  As Herceptin reaches those cells with excess Her 2 neu proteins it attaches to those proteins and eventually deposits the DM1 drug inside the cell. The DM1 then targets another protein, tubulin, causing the cell to die. Sometimes some of this drug breaks free before it reaches the cell and travels throughout the body hence the reason I am having one of the more common side-effects--low platelets. Some Herceptin never reaches its destination either causing side-effects of its own. go to link -- How Kadcyla works
TDM-1 also has a longer half-life than other drugs so it stays in the body longer.

"A drug's half-life is the amount of time it takes for a drug to lose half of its strength in blood plasma. This is most easily measured in medications administered through an injection or IV drip."
Explanation of half-life link. 
It was a relief to be treated again. I felt like I was no longer swimming in the ocean without a safety net while sharks circled me, waiting.  

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