oscar linares <winsaam <at> gmail.com> writes: > > 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) > [snip] > 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.
You set options(digits=2), thus AR is only printed to 2 digits (2.4), when its true underlying value is (at least to machine precision) options(digits=20) > 1/(1-exp(-k*tau)) [1] 2.357362278468023 Note that options(digits=2) affects only the display of numeric values, not their underlying values. You have also done some rounding of intermediate values, which is probably a bad idea. Reading R FAQ 7.31 might be useful as well. May I respectfully suggest that you not use a system that you don't understand to compute the dosages of highly toxic drugs ????? Ben Bolker ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
