# PharmPK Discussion - Calculating half-life

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• On 28 May 2001 at 20:28:20, "Milos Zarkovic" (mzarkov.-a-.EUnet.yu) sent the message
`The following message was posted to: PharmPKDear Colleagues,I need to calculate the half-life of endogenous LH inhypogonadotrophic subjects. They all havehypogonadotrophic hypogonadisam (LHRH deficiency).All subjects were primed for a week by the subcutaneousLHRH pulsatile infusion, and then LHRH bolus was given i.vand LH response was measured. What would be the best wayto calculate LH half-life, and what software to use?(Using exogenous LH would be inappropriate due to differentglycosilation).Faithfully,Milos Zarkovic, MD, PhDAssociate Professor of EndocrinologyMilos ZarkovicInstitute of EndocrinologyDr Subotica 1311000 BelgradeYugoslavia`
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• On 15 Jun 2001 at 20:04:30, Michael Leibold (ML11439.-at-.goodnet.com) sent the message
`The following message was posted to: PharmPKDr. Zarkovic,     There are mathematical models for endocrine systems which differfrom the standard pharmacokinetic equations:     Carson, E.R. et al, The Mathematical Modeling of Metabolic and Endocrine     Systems, New York, Wiley Interscience 1983     However, in a basic pharmacokinetic sense, the system you describe couldbe approximated as an infusion with bolus equation:      Cp=  Xoe-ket  +   [Ko/keVd][1-e-ket]     In the above case, the plasma levels of the endogenous LH could be fit tothis equation by nonlinear regression analysis. The infusion would representthe basal secretion, while the bolus would represent the LH released afterthe injection of the LHRH.     Another possibility is to model the plasma levels as a first order releaseprocess after the LHRH injection, while the basal secretion could still bemodeled as an infusion:     Cp=  [kaFD/(ka-ke)Vd][e-ket - e-kat]  +  [Ko/kdVd][1-e-ket]     The plasma levels resulting from basal secretion could be subtracted fromthose measured following the LHRH bolus to remove the second term from theabove equation, and simplify the fitting process.     Using equations similar to any of the above, the Ke and T1/2 for LH couldbe obtained from fitting the selected model to the observed plasma levels.However,the mathematical model for insulin secretion as described in Carson et aldiffersconsiderably from this basic pharmacokinetic analysis.                                                            Mike Leibold,PharmD, RPh                                                              ML11439.at.goodneML11439.at.goodnet.com`
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