Tracing the rise and fall of drug molecules in the human body is beginning to pay off. Consider cardiology, where pharmacokinetic studies have already provided the clinician with practical guidelines for optimal dosing with lidocaine; now we learn that tissue levels of procainamide hydrochloride, another antiarrhythmic agent, can be assayed quite simply in saliva. In fact, salivary levels mirror procainamide's pharmacologic actions more accurately than do its plasma levels.
University of California (San Francisco) investigators gave 500 mg of procainamide hydrochloride intravenously to selected subjects. From the drug's subsequent concentration profiles in plasma, urine, and saliva, they then constructed a mathematical model corresponding to a two-compartment kinetic system— with a separate third compartment accounting for procainamide movement into and out of saliva (Clin Pharmacol Ther 20:278-289, 1976). Concurrently, procainamide's therapeutic effect was gauged from alterations of the QT interval.
Over the years, we have come to accept that a drug's