Pharmacokinetic Interpretation of Data Gathered during Therapeutic Drug Monitoring

We review some pharmacokinetic principles that can fa-cilitate interpretation of data obtained during therapeutic drug monitoring: the one- and two-compartment models, volume of drug distribution, drug clearance, organ clear-ance, bioavailability, first-pass effect, chronic or repetitive dosing, and use of urine and saliva to measure drug clearance and drug binding to plasma proteins, respec-tively. 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. AddftlonalKeyphrases: “biologic half-life ” of a drug #{149}drug distribution and clearance #{149}drug binding to plasma proteins #{149}urine or saliva as the sample in drug monitoring #{149}dos-age/concentration relations Clinical chemists are frequently requested to identify and quantitate a wide variety of drugs in the blood and urine of acutely poisoned patients. To this extent, re-sponsibility for verification and treatment of drug toxicity rests with clinical chemists, because they fur-nish the information that forms the basis for therapy. Recent developments in pharmacology and medicine indicate that under some circumstances measurement of drug concentration in blood is the best available guide to ascertain each patient’s particular dose requirements (1, 2). Such circumstances include: (a) high incidence of toxicity resulting from certain drugs used alone or in combination; (b) failure to attain adequate pharmaco-logic responses after administration of potent drugs with low therapeutic indices given in the usual doses; (c) interactions of concomitantly administered drug