Encyclopedia of Clinical Neuropsychology

2018 Edition
| Editors: Jeffrey S. Kreutzer, John DeLuca, Bruce Caplan

Half-Life

  • Jose A. ReyEmail author
Reference work entry
DOI: https://doi.org/10.1007/978-3-319-57111-9_1739

Definition

The half-life of a drug (t1/2) is the time it takes for the blood or plasma concentration of a given drug to be reduced by 50%.

The formula for calculating this value is t1/2 = 0.693 · Vss/CL.

This pharmacokinetic value is also important for determining the time to steady-state concentrations in the body. It takes approximately five half-lives for a drug to achieve steady-state plasma concentrations in the body, which signifies that the amount of the drug being eliminated from the body is equal to the amount of the drug being administered. Subsequently, a medication usually requires approximately five half-lives for a significant majority (~97%) of the drug to be eliminated from the body after discontinuation. The half-life of a drug may influence or dictate the daily dosage regimen of a particular agent and also the amount of time needed to achieve a needed and consistent response for efficacy; and a medication’s (or drug of abuse) half-life may also provide an indication...

This is a preview of subscription content, log in to check access.

References and Readings

  1. Brunton, L. L., Chabner, B. A., & Knollman, B. C. (Eds.). (2011). Goodman & Gilman’s the pharmacological basis of therapeutics (12th ed.). New York: McGraw-Hill.Google Scholar
  2. Cooper, J. R., Bloom, F. E., & Roth, R. H. (Eds.). (2003). The biochemical basis of neuropharmacology (8th ed.). New York: Oxford University Press.Google Scholar
  3. Davis, K. L., Charney, D., Coyle, J. T., & Nermeroff, C. (Eds.). (2002). Neuropsychopharmacology: The fifth generation of progress. Philadelphia: Lippincott Williams & Wilkins.Google Scholar
  4. Stahl, S. M. (2013). Stahl’s essential psychopharmacology: Neuroscientific basis and practical applications (4th ed.). New York: Cambridge University Press.Google Scholar
  5. Voet, D., Voet, J. G., & Pratt, C. W. (Eds.). (2016). Fundamentals of biochemistry: Life at the molecular level (5th ed.). New Jersey: Wiley.Google Scholar

Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  1. 1.College of PharmacyNova Southeastern UniversityFt. LauderdaleUSA