Dear Rxperts,

Running the following code:
=======================================================
twlo=10; twhi=20; wt=154; vd=0.5; cl=0.046; tau=6; t=3; F=1;

wtkg  <- wt/2.2             # convert lbs to kg

  vd.pt <- wtkg * vd       # compute weight-based vd (L)
  cl.pt <- wtkg * cl       # compute CL (L/hr)
  k     <- cl.pt/vd.pt     # compute k (hr^-1)

  cave      <- round((twhi - twlo)/log(twhi/twlo),2)
  doserate  <- (cl.pt * cave)/F

  # maintenance dose (Dm)
  total_dose_tau <- round(doserate * tau,0)

  Cmax <- total_dose_tau/vd.pt
  Cmin <- Cmax * exp(-k * tau)

  AR <- 1/(1 - exp(-k * tau))

  Cmaxss <- Cmax * AR
  Cminss <- Cmin * AR
  Cfluctss <- (Cmaxss - Cminss)
  Ct       <- (Cmaxss * exp(-k * t))

  dose_loading_vd <- round(Cmaxss * vd.pt,0)
  dose_loading_dm <- round(total_dose_tau * AR,0)

  options(digits=2)

c("Ther. Win. (mg)"=twlo,"to"=twhi,"Wt (kg)"=wtkg,"Vd (L)"=vd.pt,"CL
(L/hr)"=cl.pt,"Cave (mg)"=cave,"D/tau (mg/hr)"=doserate,"tau
(hr)"=tau,"Total Dose (mg)"=total_dose_tau,"Cmax (mg)"=Cmax,"Cmin
(mg)"=Cmin,"AR"=AR,"Cmaxss (mg/L)"=Cmaxss,"Cminss (mg/L)"=Cminss,"Cfluct
(mg/L)"=Cfluctss,"C(t) (mg/L)"=Ct,"DL wVd (mg)"=dose_loading_vd,"DL wDm
(mg)"=dose_loading_dm)
===========================================================================
Gives
Ther. Win. (mg)              to         Wt (kg)          Vd (L)       CL
(L/hr)       Cave (mg)
           10.0            20.0            70.0            35.0
3.2            14.4
  D/tau (mg/hr)        tau (hr) Total Dose (mg)       Cmax (mg)       Cmin
(mg)              AR
           46.5             6.0           279.0             8.0
4.6             2.4
  Cmaxss (mg/L)   Cminss (mg/L)   Cfluct (mg/L)     C(t) (mg/L)     DL wVd
(mg)     DL wDm (mg)
           18.8            10.8             8.0            14.3
658.0           658.0

But, there is an error from R?

AR * total_dose_tau = 658 but that is wrong

Total Dose (mg) = 279 * AR (=2.4) = 670

Please help. I don't want to harm anyone. A difference of 12 mg of a highly
toxic drug can at the very least cause significant harm.


-- 
Oscar
Oscar A. Linares, MD
Translational Medicine Unit
La Plaisance Bay, Bolles Harbor
Monroe, Michigan 48161

Department of Medicine,
University of Toledo College of Medicine
Toledo, OH 43606-3390

Department of Internal Medicine,
The Detroit Medical Center (DMC)
Harper University Hospital
Wayne State University School of Medicine
Detroit, Michigan 48201

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