Using Pharmacogenetic Testing in a Pain Practice
Pharmacogenetic testing (PGT) is an objective clinical tool that has the potential to help clinicians improve treatment in many areas of medicine, including pain management. PGT can be a vital component of personalized medicine, assisting clinicians in choosing medications based on patient genetics to increase benefit and decreased risks.
PGT also can be a valuable tool for troubleshooting when patients are having idiosyncratic reactions, require higher than normal doses, or simply exhibit poor response to a specific medication or a class of medications. Finally, PGT can play an important role in facilitating doctor–patient communication about expectations, outcomes, and adherence as well as patient education about the role of genetics in determining, in part, outcomes related to opioid therapy.
In pain management specifically, PGT gives clinicians insight and guidance on the management of complicated patients with chronic pain who may have struggled with problematic side effects or suboptimal benefits from medications such as opioids.1,2 Abnormal PGT results in complicated chronic pain patients are relatively common.3 PGT provides information that can help clinicians guide personalized treatment plans, identify medication metabolism abnormalities, clarify urine drug testing (UDT) results, improve patient functional outcomes, avoid potential medication interactions, and guide therapeutic decisions such as changing medication dose, or rotating opioids.4-10 This information, combined with general risk assessment strategies, a thorough history and physical examination, knowledge of potential concomitant medication interactions, and UDT can improve clinicians’ understanding of the unique and highly individualized responses to pain treatment so often seen in specialty care settings.11,12
The out-of-pocket costs associated with obtaining PGT are not negligible and must be considered. However, substantial costs savings eventually might be realized throughout the healthcare system if PGT realizes its full potential in the avoidance of unnecessary trial and error in drug selection. Thus, as with all tests, there is a need to document the medical necessity and purpose for ordering PGT and to demonstrate the subsequent use of the results in patient care.
One of the authors (Eric Ehlenberger) has a large medical practice in Louisiana, where he has been ordering PGT on all new patients treated for chronic pain at his facility. He had been struggling with a large number of patients with difficult and idiosyncratic reactions to commonly used medications and also was trying to manage the polypharmacy that typifies the management of refractory pain by the time patients end up in specialty pain care. His regular use of PGT presented an excellent setting for the piloting of a study on the documentation of the uses of PGT in the areas of treatment planning, troubleshooting, and support of doctor–patient communication and patient education.
This study reports on the results of a structured chart review of patients with chronic pain receiving opioid therapy for whom PGT had been ordered (samples submitted to a laboratory for PGT on 3 subtypes of the cytochrome P 450 [CYP450] enzyme system [CYP2B6, CYP2C19, and CYP2D6] and 1 test on the UGT [UGT2B15] enzyme) using a chart review tool to examine instances of documentation of the uses of PGT in clinical care.
How the Study Was Designed
For the purposes of this research study, which was approved by Aspire IRB in San Diego, California, the researchers developed a novel checklist to assess the effects of PGT results on patient care (Figure 1). Two trained research assistants used this checklist on de-identified medical records of 85 patients from a single physician’s office. The PGT was conducted on the patients to assess safety prior to prescribing medications and/or as a clinical test for a differential assessment due to negative outcomes (excessive side effects, intolerance of medications, lack of efficacy, etc.)
The researchers used the checklist to record data from 2 visits: the “baseline” visit, when the patient PGT was originally ordered, and the first visit after the report was received (the first opportunity for the results to be presented to the patient). They used patient history, PGT results, medications, and office visit notes to complete the checklist, and categorized the changes made and their effects on the subsequent patient visit using a binary coding system (checkbox marked or left blank).
Results of the Study
The researchers randomly selected 85 charts of patients who had PGT from Millennium Laboratories between the dates of November 28, 2012 and December 16, 2013. The population was 67% male, with an average age of 45 (±10) years.
The most common pain diagnosis among study patients was low back pain (n=57; 67%), followed by neck pain (n=14; 16%). A full description of the population’s diagnoses can be found in Table 1.
The majority of instances of documentation about the use of PGT results were for patient education (n=72; 85%), cooperative treatment decision making (n=58; 68%), and support for increases (n=16; 19%) or decreases (n=10; 12%) in medication dosages.
PGT Phenotype Results
Table 2 displays the genetic results for each of the 4 genes tested on each saliva sample. The rates for extensive (or normal) metabolizers was 84.7% for CYP2D6, 42.4% for CYP2C19, 56.5% for CYP2B6, and only 18.8% for UGT2B15.
Using the study checklist to evaluate each patient’s chart, the research team identified the most commonly noted impact of the PGT. Due to the retrospective nature of this study, these data only are able to evaluate the effects noted as a part of standard patient notes. The most commonly noted impact of the PGT was related to educating patients about how their PGT status would be used to make changes or maintain their present medication regimen. This was specifically noted in 85% (n=72) of the charts analyzed. The other most commonly noted result was the physician reviewing results and using them to contextualize the patient’s prior pain experiences, side effects, and pain relief (68%; n=58).
In addition to visit notes, the checklist also was used to track changes in medication dose and type. Of the 85 patients, 47% (n=40) had some change in their medication regimen during the visit immediately following the release of their PGT results. A full summary of the most common noted actions can be found in Table 3.