The Estimation of Basic Organic Compounds in Biological Material

Simple and reliable methods for the measurement of the concentration of therapeutic agents in biological materials greatly facilitate the study of the agent's physiological disposition, upon which sound therapy must be based.The intermediate metabolism of a therapeutic agent cannot be studied in the absence of methods for its estimation.And finally, knowledge of the concentration of an agent in the tissues and fluids of the host, animal or human, is of considerable value in studying the mechanism of drug action.Unless the concentration in viva of an agent, achieved in a specific tissue after therapeutic dosage, is known, the interpretation of studies in vitro with the agent is open to question.The problem of devising analytical procedures for the est.imation of a large number of compounds, in connection with an antimalarial clinical testing program, was simplified by a scheme for the analysis of basic organic compounds.The principles involved in this scheme are presented here and should be applicable to the development of methods for other basic therapeutic agents.The various methods, with examples to illustrate their sensitivity and specificity, will be described in subsequent papers.The scheme involves the isolation of the compounds from their metabolic products and from normally occurring substances by extraction procedures.The concentration of the compound is increased if necessary by returning it to a small aqueous phase.The method for the final estimation is determined by the properties of the compound and depends on fluorometry or photometry.A general technique of appraising specificity is based on a comparison of the solubility characteristics of the pure compound with those of the material extracted from the biological material obtained from a host to which the drug has been administered.Data obtained from this comparison may be used to modify the initial extraction procedure so as to separate interfering drug metabolites from the unchanged drug.