What is half-life and why is it important for immunotherapy drugs?

Several forms of immunotherapy involve the use of drugs to modulate the immune system. The half-life of a drug (t1/2) is the period needed for a known quantity of drug to be reduced by 50% after being introduced into a body. Half-life is a critical parameter, as it monitors whether the body is metabolizing the drug, storing it compartments such as fat depots, or destroying it for removal. Vital pharmacokinetic parameters for half-life include clearance and volume distribution. Clearance refers to the rate at which a drug is removed from a patient’s plasma. The volume of distribution monitors the translocation of a given bolus of medication throughout various organ compartments in the body.1

1. C.A. Wesolowski, et al., "Time Varying Apparent Volume of Distribution and Drug Half-Lives Following Intravenous Bolus Injections," PLoS One 11(7): e0158798, 2016.