Staggered stable isotope administration technique for study of drug distribution

By infusing intravenously a series of different stable isotope labeled forms of a drug at different times prior to performing a single collection of a body fluid via puncture (or tissue via biopsy), one can obtain the same information about a drug's distribution as would be obtained by infusing a single dose of drug and performing serial collections of fluid (or tissue). Application of this technique of "staggered stable isotope administration" is illustrated with a study of entry of phenobarbital into the cerebrospinal fluid of a dog. Advantages and disadvantages of this technique are discussed.