You may have heard the term “pharmacokinetics” – or “PK” – but what does it mean? Why is it important? Here is a quick guide to help you get started.
Pharmacokinetics is the study of the bodily absorption, distribution, metabolism, and elimination of drugs. Using PK testing, your doctor can identify your unique PK profile and create a personalized treatment plan based on how drugs are taken into, moved around, broken down, and eliminated from your body.
The aim of hemophilia A treatment is to continuously maintain factor VIII at high enough levels with regular infusions to reduce the frequency of bleeding episodes – but specific treatment details vary from person to person.
No two people have the same PK profile, which is why it’s important to speak with your doctor about conducting PK testing. To do so, your doctor measures factor VIII levels using blood samples taken after one or more of your regular treatment infusions over time. Then, your doctor will measure factor VIII levels in each sample to generate your PK profile.
A current PK approach, population PK, also considers physiological factors that have been shown to impact factor VIII dose concentration (such as body weight) and uses predictive modeling to help assess your PK profile. This approach requires fewer blood samples to determine your profile than traditional PK testing.
When you and your physician review your PK profile, you’re likely to hear a few new terms: Peak, Area Under the Curve (AUC), Half-Life, Clearance, and Trough Level. To break these down, it’s helpful to think of your factor VIII product as your cell phone and your PK profile as your phone’s charge.
Peak is the maximum level of factor in your bloodstream after an infusion. In other words, when your cell phone is 100% charged.
Area Under the Curve (AUC) is the total amount of factor distributed in the blood stream over a period of time. For your phone, AUC is amount of charge used before the phone charge runs out. Higher AUC means more factor is available between infusions.
Half-Life refers to the time it takes for factor levels to reduce by half after an infusion. Think of this as the time your phone takes to go from full to half charge. Longer half-life means more sustained levels of factor VIII in the body.
Clearance is the speed at which factor is eliminated (or how quickly a phone battery loses charge). The lower the clearance rate, the longer factor VIII is available in your body.
Trough Level is set individually with your doctor based on your personal needs and determines the factor levels at which to schedule your next infusion. You can think of this as the minimum amount of battery needed to prevent your phone from running out of charge.
Talk to your physician about obtaining your PK profile and check out the video on this page for a closer look at PK terms. To learn more about PK and explore additional PK resources, visit LivingWithHemophilia.com.