PharmPK Discussion - First-order one compartment formulas

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• On 14 Feb 1997 at 17:58:08, djtippey.-at-.dbtech.net (Del & Jackie Tippey) sent the message
`Greetings;        I am working on a PK program for my department's aminoglycoside /vancomycin PK program. I have equations that will give me estimates oflevels and Vd after "n" doses - provided it is the initiation of therapy. Iwas wondering if anyone knew of equations that could help me determinelevels after "n" doses if I had a ballpark pre-therapy level. I know thatthe steady-state equations probably will remain the same, but I wanted toknow in case levels are drawn before steady-state so we determine expectedlevels.        Thanks in advance...        -DT-`
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• On 18 Feb 1997 at 11:48:45, "David Nix" (nix.aaa.tonic.Pharmacy.Arizona.EDU) sent the message
`The full equation for concentrations at any time is:C(t) = D/TI/ke/V*(exp(-k*ts)-exp(-k*t))*(1-exp(-nktau))/(1-exp(-ktau))       D=dose       TI=time of infusion       k=elimination rate constant       V=volume       ts=t-TI  :    restrict ts>=0       tau = dosing interval       n = # of doses givenThere are several bayesian estimation programs commercially availablethat will handle 1 or more non-steady-state levels.  However, if acomputer and software are not available, some other methods may beuseful.  Below is how I have handled similar problems:Single level:     1.  assume k based on creatinine clearance     2.  calculate V from the above equation     3.  If volume is reasonable (.24 to 0.4 L/kg for aminoglycoside)          then accept new parameters.  Otherwise, you may adjust ke          by 20-40% and recalculate V.  This method will get parameters in the         "ball park".Two levels     1. Within same dose interval.  Use levels to estimate k, then          calculate V as above.     2.  trough-dose-peak -  This senerio provides a better estimate          of V than ke.  However, you must calculate ke by trial and error.          Guess at ke and calculate V based on one of the levels.  Then check          to see if the other level is predicted correctly.  After some          practice, this process does speed up considerable, but it is still          time consuming.  Your speed is related to your ability to guess at k          and revise the estimate, and also how close that you are trying to          approach the measured concentrations.The use of computers and baysian approach is recommended.`
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• On 25 Feb 1997 at 12:36:16, djtippey.aaa.dbtech.net (Del & Jackie Tippey) sent the message
`Thanks for the rapid and informative feedback.-DT-Del Tippey R.Ph., M.S.S.M.DCH Regional Medical Center801 University Blvd. E.Tuscaloosa,AL 354051-205-759-7310djtippey.aaa.dbtech.net`
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