This is very similar to virtually every other definition you might find out there.В The half-life chapter of the official college pharmacology textВ starts with the following definition: Half-life (tВЅ) is the time required to change the amount of a drug in the body by one-halfВ during elimination. The college in their half-paragraph answer to Question 11В from the second paper of 2012 offered the following definition: This article discusses the limitations of this concept when applied to real-life situations. For an alternative, one may wish to read David Greenblatt'sВ article from 1985. This is certainly enough to pass the exam. The official college pharmacology text (Birkett et al, Pharmacokinetics Made Easy - 2009) has an entire chapter dedicated to half-life (Chapter 3, p.30-38). With zero-order kinetics the term becomes meaningless, andВ one refers instead to a dose or concentration removed over time. For drugs eliminated by first-order kinetics, half life is constant regardless of concentration.Doubling the dose of a drug will usually increase its duration of action by one half-life (because its clearanceВ is a logarithmic function).It takes about 5 half-lives for a drug to be roughly 97% eliminated.

renal failure with oedema) volume of distribution increases but clearance decreases, resulting in an unchanged half life (thus, it is a poor measure of drug clearance alone).

Half life is increased by an increase in the volume of distribution and increasedВ by a decrease in the rate of clearance.0.693 is the logarithm of 2, and represents the exponential rate of elimination (assuming elimination is byВ first order kinetics).Volume of distribution (Vd) and clearance (CL) are required to calculate this variable.The formula for half-life is (tВЅ = 0.693 Г— Vd /CL).Half-life (tВЅ) is the time required to reduce the concentration ofВ a drugВ by half.

How many chapters in half life