Background:

Pharmacogenomics (PGx) is a developing field in individualized medicine concerned with understanding genetic polymorphisms that may explain inter-individual variation in drug efficacy and toxicity. Understanding these polymorphisms is a key tool in guiding clinician’s selection and dosing of specific medications to optimally manage patient symptoms. Common pharmacogenes that impact analgesic prescribing include: CYP2D6, OPRM1, and COMT; for mood disorders: CYP2C19. This cross-sectional study explored the activity of pharmacogenes of clinical significance in palliative medicine with either Level 1 or 2 evidence.

Methods:

We performed PGx testing on 50 new referrals to the palliative medicine clinic with an active malignancy. Each patient underwent PGx testing with clinical pharmacist review and interpretation prior to their initial office appointment.

Results:

In our cohort 54% were men and the mean age was 64.7 (24-87). The average number of medications, medication allergies, and creatinine clearance were 10.5 (1-22), 1.3 (0-13), and 78.4 (31-120), respectively. Among the pharmacogenes impacting opiate and antiemetic prescribing, 14% (7/50) of patients were poor metabolizers of CYP2D6 and 8% (4/50) were rapid or ultra-rapid metabolizers. Another 60% (30/50) showed intermediate metabolism which would impact initial dosing. Poor metabolism of COMT or OPRM1 was seen in 8% (4/50) with another 36% (18/50) demonstrating rapid metabolism. Activity for the pharmacogene CYP2C19, which impacts many psychotropics, revealed 32% (16/50) rapid or ultra-rapid metabolizers and no poor metabolizers. Overall, 66% (33/50) of patients had pharmacogene activity suggestive of significant clinical impact necessitating either drug avoidance due to toxicity risks or substantial dose adjustment to be efficacious.

Conclusions:

Polymorphisms impacting pharmacotherapy were common in our cohort. Patients with difficult-to-control symptoms or multiple medication toxicities can utilize PGx testing as a guide to symptom relief. As PGx technology becomes readily accessible and economical, opportunities for patients to have precision genomic information guide healthcare decisions is expected to increase.