Pharmacokinetic interpretation of data gathered during therapeutic drug monitoring

We review some pharmacokinetic principles that can facilitate interpretation of data obtained during therapeutic drug monitoring: the one- and two-compartment models, volume of drug distribution, drug clearance, organ clearance, bioavailability, first-pass effect, chronic or repetitive dosing, and use of urine and saliva to measure drug clearance and drug binding to plasma proteins, respectively. We also describe use of saliva to estimate rapidly, conveniently, and noninvasively the concentration of the free, pharmacologically active form of the drug as well as the fraction of drug bound to plasma protein.