| Quantitative urine drug screens obtained by LC-MS/MS are limited in their interpretation because the relationship between drug dosage and excretion can be highly variable due to pharmacogenomic and other patient differences. However, LC-MS/MS analyses for an individual patient can also measure one or more metabolites along with the parent drug, such as morphine/hydromorphone. We have established a patient database of the metabolic ratio (metabolite divided by parent drug molar concentrations) of several drug pairs, and defined the usual inter- and intrapatient expected range values. These can be used to monitor variances in an individual’s metabolism of a specific drug over time. |
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