How Half-Life of Factor Really Works

by Andy Matthews with Dr. Mike Wang

Bleeds were very common, in the 1970’s when I grew up.  The reason for that was that most people did not have access to factor, and many did not have the capability to use factor or Cryoprecipitate at home.  However, even today, there are many reasons why adult and pediatric patients are still experiencing ongoing bleeds and joint damage, including: inhibitors, spontaneous joint bleeding and bleeding that is hard to control.  Another reason may be that people do not understand their factor half-life.  By understanding half-life you may cut back on the number of bleeds you have per year, and thus protect your joints even more.  It is very damaging to keep bleeding into a joint over time, and this is something that can be either cut back or prevented almost altogether.

The main goal in managing your or your child’s hemophilia should be this: prevent joint damage!  You want to stop recurrent bleeding in joints at all cost, end of story!  If you do not, you will destroy your joints since blood in the joints will keep damaging them.  Blood is supposed to stay in the veins, and synovial fluid is supposed to be in the joint space making them move smoothly.  I have a bad ankle due to lots of bleeds when I was a kid because I wasn’t able to do prophylaxis, and I continue to suffer from it.  Today, however, I am very active so the only way I can stay in shape and prevent bleeds is to be on a very rigorous prophylaxis schedule, of every other day infusions, so that I always have some factor in me.

This brings us to the title of our article- understanding the half-life of factor.  Many people do not fully understand half-life.  The problem with factor eight and nine is that they have very short half-lives.  For most people with a factor eight deficiency, the half-life is an average of 12 hours.  This, of course, depends on the patient’s body and the brand of factor being used, but for argument’s sake, let’s just stay with the average, a 12 hour half-life.   To figure the half-life: when you infuse to get up to a 40% factor 8 level, just cut that level in half every 12 hours. So, by 48 hours, most people would have around 2.5% factor 8 or less left in their bodies. 

Basically, when you infuse, you are trying to turn yourself into a person with mild hemophilia, and most people with mild hemophilia do not bleed, and they often can live more normal lives. Often times, people will tell me they are dosing with factor only once or twice a week, which leaves them unprotected for a lot of the week. 

Factor nine is about the same as factor 8, but it has about a 16 hour half-life.  So, most factor 9 patients need to infuse about every three days. 

The main point of this article is to get you to examine your infusion schedule, which will help you minimize joint bleeds.  For me, it’s prophylaxis.  You should talk to your doctor to make sure you are on the right plan to keep joint bleeds to a minimum.  In most cases, every time you have a bleed into a joint, you are doing more damage, so learn your half-life and infuse accordingly!  Let’s keep joint bleeds to a minimum and reduce or stop joint damage all together. 

 

Factor 8 Half-Life (figured with a 12 hour half-life)

Day/Time of Infusion:% Correction:Units/Kilos of Weight:
Monday, 8:00AM:00AM40%20 units/kilo
Monday, 8:00PM20% 
Tuesday, 8:00AM10% 
Tuesday, 8:00PM5% 
Wednesday, 8:00AM2.5%Ready for next infusion
 
Monday, 8:00AM80%40 units/kilo
Monday, 8:00PM40% 
Tuesday, 8:00AM20% 
Tuesday, 8:00PM10% 
Wednesday, 8:00AM5% 
Wednesday, 8:00PM2.5% 
Thursday, 8:00AM1.26%Ready for next infusion
 

Factor 9 Half-Life, figured with a 16 hour half-life

Day/Time of Infusion:% Correction:Units/Kilos of Weight:
Monday, 8:00AM40%  units/kilo
Tuesday, 12:00AM20% 
Tuesday, 4:00PM10% 
Wednesday, 8:00AM  5% 
Thursday, 12:00AM2.5%Ready for next infusion

 

Factor 8 Formula:    Dosage Required (IU) = Body Weight (kg) x Desired Factor VIII % Increase (IU/dL or %normal) x 0.5 (IU/kg per IU/dL)

Factor 9 Formula:   Dosage Required (IU) = Body Weight (kg) x Desired Factor IX % Increase (IU/dL or %normal) x 1 IU/kg

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