Adjustment for early or late drug concentrations

Since we are approximating two-compartment kinetics by employing a one-compartment equation in the terminal (i.e. elimination) phase of the plasma drug concentration versus time curve, the elimination rate constant K can be substituted for A, to give  

Specifically, if a peak plasma concentration (Cp)Hi is sampled somewhat late (e.g. 1.5 h late), the above equation can be used to adjust (Cp)Hi to the (higher) plasma drug concentration that would have been recorded if the concentration had been collected on time. Then, 

we ought to consider whether any other possibilities exist besides the two cases just described. For example, could a peak concentration need adjustment because it was collected too early In fact, this case would represent a real problem since the drug concentration would have been collected in a part of the curve where distribution is still going on. Adjusting the observed concentration with the monoexponential equation would not be appropriate in this case since it would generate an erroneous estimate of the peak concentration. 

Both peak and trough concentrations are collected on time according to the guidelines for the particular drug. 

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Example problem adjustment for early or late drug concentrations... 

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