ABSTRACT
The levels of therapeutic drugs in blood or urine are not actually measured in most instances. The clinical effectiveness of drug therapy, rather than actual assay, is used as the regulation of dosage. This chapter summarizes drugs and other substances which may interfere with the results of urinalysis procedures. As the interference of drugs is studied, it becomes apparent that it is often not the drug itself but its metabolites which cause the problem. One of the early recognitions of the effect of a metabolite and the lack of effect of the drug itself is referred to by Caraway. Orally administered quinine increases the apparent urinary catecholamine level; this is presumably a metabolite effect since the direct addition of the drug to urine has no affect on the assay. There are other investigators who appear to believe that there may be a tendency to overreact to drug interference with laboratory results or to overexaggerate their importance.
