Why Determining Drug Dose in Urine is a Myth

I have had several conversations where I have been asked if urine levels depict the dose and frequency of drugs detected in the urine. There is concern for both prescription medications (prescribed by that clinician or prescribed by other clinicians) and non-prescribed drugs. Clinicians need and want to determine a patient's adherence and extent of patient adherence. We also want to know if the medication, dose, and frequency prescribed is the best combination for our patient. We need to know how the patient is taking their medication so we can prescribe or adjust their medication accordingly. If a person takes too much or is not taking their medication, they can become ill either because of the medication or because the condition is not being treated appropriately. For these reasons and many more, it is understandable that clinicians are looking for a measurement that tells them specifically the drug dose and frequency that a patient is taking. Unfortunately, drug dose cannot be determined in a urine specimen. The only way you can know exact oral dosage and frequency is if you administer each dose to that patient.

Anne Nafziger, MD, MHS, PhD and Joe Bertino, Jr., PharmD, FCP, two clinicians who both have over 20 years of experience in drug development, clinical pharmacology, and clinical research and are also authors of the UDM: Opioids handbook, have published an exceptional article titled "Utility and Application of Urine Drug Testing in Chronic Pain Management With Opioids" in the January 2009 issue of the Clinical Journal of Pain. The article specifically describes the inability to determine oral drug dose in urine. One primary reason is genetic variations among people. A patient's genetic profile contributes to the rate and extent of ADME (absorption, distribution, metabolism, excretion). The genetic makeup of individuals is unique and therefore drug ADME is unique to that person. The article also states that in addition to differences between individuals, ADME may vary within a single person on a day to day basis. Due to these facts among others covered in the article, the authors state "...without blood concentration data, evaluating quantity of excreted parent drug in urine will not provide unequivocal evidence of patient ...(adherence) with recommended dosing."

So where do we go from here? Ultimately the goal is give our patients optimal pharmacotherapy. Currently, in the clinician-patient relationship, there is information we may collect and analyze to assist in assessing patient adherence. To move even closer to our goal, we need to utilize new tools and state-of-the-art technology. The motivation to write the UDM:Opioids handbook stemmed from the need for clinicians to obtain this information. Because UDM is a comprehensive monitoring strategy, it can provide more clinically relevant information than strictly knowing if the patient is taking the exact dose prescribed at the exact frequency prescribed. This will help shift the focus from drug dose to drug efficacy, and that is what will truly enhance our patients' treatment outcomes.