What is Half-Life and Why Do I Need to Understand It?

Discuss current knowledge and potential misconceptions of half-life

NHF 2015 (Dallas, August 13-15) A patient/caregiver-focused session at the National Hemophilia Foundation (NHF) 2015 Annual Meeting explained the concept of half-life and why it is important for hemophilia patients to understand it. The elimination half-life of a drug is the time necessary for the drug to be reduced to half of its original level in the body. This means the longer the half-life, the longer it will take the drug to be eliminated from the body. For example, let’s say that drug X has a half-life of 48 hours. This means that if a patient takes drug X at 2:00 pm on Tuesday, then by 2:00 pm on the following Thursday, there will be half the amount of drug left in the patient’s body than there was after the patient took the drug. The concept of half-life is important to understand because it determines the dosing schedule of a drug. It helps a health care professional determine how often a drug must be given to the patient to keep the drug level at an optimal level in the patient’s body. The concept of half-life is important for patients with hemohilia to understand because it is used to describe how factor levels change in the blood over time, so for example if your factor level is 100% right after taking factor, at one half-life later (~10-12 hours for factor VIII), your factor level would be 50%.