A pre-loaded example dataset in R

Main page: https://www.rdocumentation.org/packages/datasets/versions/3.6.2/topics/Theoph

head(Theoph)
##   Subject   Wt Dose Time  conc
## 1       1 79.6 4.02 0.00  0.74
## 2       1 79.6 4.02 0.25  2.84
## 3       1 79.6 4.02 0.57  6.57
## 4       1 79.6 4.02 1.12 10.50
## 5       1 79.6 4.02 2.02  9.66
## 6       1 79.6 4.02 3.82  8.58
require(stats); require(graphics)
coplot(conc ~ Time | Subject, data = Theoph, show.given = FALSE)

Theoph.4 <- subset(Theoph, Subject == 4)
fm1 <- nls(conc ~ SSfol(Dose, Time, lKe, lKa, lCl),
           data = Theoph.4)
summary(fm1)
## 
## Formula: conc ~ SSfol(Dose, Time, lKe, lKa, lCl)
## 
## Parameters:
##     Estimate Std. Error t value Pr(>|t|)    
## lKe  -2.4365     0.2257 -10.797 4.77e-06 ***
## lKa   0.1583     0.2297   0.689     0.51    
## lCl  -3.2861     0.1448 -22.695 1.51e-08 ***
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## 
## Residual standard error: 0.8465 on 8 degrees of freedom
## 
## Number of iterations to convergence: 7 
## Achieved convergence tolerance: 2.969e-06
plot(conc ~ Time, data = Theoph.4,
     xlab = "Time since drug administration (hr)",
     ylab = "Theophylline concentration (mg/L)",
     main = "Observed concentrations and fitted model",
     sub  = "Theophylline data - Subject 4 only",
     las = 1, col = 4)
xvals <- seq(0, par("usr")[2], length.out = 55)
lines(xvals, predict(fm1, newdata = list(Time = xvals)),
      col = 4)