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For more information about pharmacokinetics parameters, including a list of questions you might want to ask your doctor, connect with your CoRe and request our helpful PK guide.
Connect with a CoReUnderstanding factor activity.
Pharmacokinetics (pharmacology + kinetics), or PK, is the study of how drugs move in the body. Understanding your unique PK parameters can help doctors evaluate factor activity levels in the body, which can help improve your hemophilia management and treatment.
What does factor activity mean for you?
People with factor activity levels above 40% are considered normal or near-normal. If a person’s factor activity level is below the 40% mark, they may have hemophilia. The exact percentage of factor activity determines whether you’re categorized as having mild, moderate, or severe hemophilia.
Factor activity & severity
Mild
≥5% to ≤40% factor
activity*†
Bleeding can occur from injury or surgery
Spontaneous bleeding is rare
Moderate
≥1% to 5% factor activity*†
Bleeding can occur from injury or surgery
Spontaneous bleeding is possible
Severe
<1% factor activity*†
Bleeding likely from injury
or surgery
Spontaneous bleeding is frequent—often into joints and muscles
*Severity classifications may be different for women with hemophilia
†Factor levels may not reflect bleeding patterns
Hemophilia type and severity
Hemophilia B is less common than hemophilia A and impacts 15% to 24% of all people with hemophilia. The charts below show the prevalence of hemophilia severity for both hemophilia A and B.
Severity in the hemophilia A population
32% Mild
16% Moderate
43% Severe
9% Other
Severity in the hemophilia B population
25% Mild
35% Moderate
31% Severe
9% Other
Higher factor levels in your body over time may provide better bleed protection. This is why many people with hemophilia use infusions of factor replacement therapy to prevent bleeds. Doctors can use PK tests to detect the level of factor activity in your blood, and then figure out your best options for treatment.
To learn more about factor activity levels and how blood clots form, visit our Levels Matter site.
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Discover the elements of a PK profile
Everybody processes hemophilia treatments differently. PK testing evaluates the factor activity levels in your blood and the severity of your hemophilia. Both are helpful when determining a treatment regimen that is right for you.
The graph below illustrates these changes in factor activity over time and highlights the key parameters doctors will evaluate when building a PK profile.
Peak
Factor activity levels are the highest in the body right after an infusion. This is called the peak.
Area under the curve (AUC)
Represents the amount of factor in your body over time.
Clearance
The speed at which factor is eliminated from the body (not shown on graph).
Half-life
The amount of time it takes for factor level to go down by 50% after an infusion. The longer the half-life of your factor is, the longer it will stay in your body to protect you from bleeds.
Trough
The lowest level of factor activity right before the next dose is called the trough level.
Volume of distribution (VOD)
A measure of how much factor is in the blood and in other tissues in the body (not shown on graph).
What to expect with PK testing
Full PK profiles are rarely completed in people with hemophilia. If your doctor does recommend a PK profile, this will include measuring factor activity levels in blood samples taken at different times after an infusion. You’ll need to go in several times to have your blood drawn and analyzed. Your doctor will then build a PK profile to help optimize treatment. Talk to your doctor about whether PK testing is right for you.
The full picture is key
Every person living with hemophilia is unique, and there are important differences between hemophilia A and B that might affect management and treatment. A complete treatment assessment may include multiple ways of measuring factor activity levels. Individual bleed rates, joint bleed prevention, and your personal goals should be considered in discussions with your doctor. Visit our Bigger Picture in Hem B site to learn more.
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