Case Report & Results
A 67-year-old Caucasian female presented with a past medical history of
chronic, intractable lower back pain, hypertension, anxiety, and heart
failure. Her physician prescribed several medications to manage her
various conditions, including oxycodone tablets, 15mg four times daily;
duloxetine capsules, 60mg once daily; lorazepam tablets, 1mg twice daily
as needed; metoprolol succinate tablets, 50mg once daily; and lisinopril
tablets, 10mg once daily. At a follow-up appointment with her physician,
she reported experiencing on going uncontrolled pain. Following multiple
increases in her oxycodone dosage, from a total daily dose of 20mg to
60mg, she continued to experience inadequate pain control. When her
physician sought assistance, the clinical pharmacist suggested that PGx
testing would be helpful to assess appropriateness of opioid therapy and
guide medication changes. The physician then ordered a PGx test.
A DNA sample was collected by buccal swab and analyzed by a genetics
laboratory. The results were then interpreted by the clinical
pharmacist. The patient was identified as an intermediate metabolizer
(IM) for the cytochrome P450 2D6 (CYP2D6) drug-metabolizing enzyme, with
a *9|*40 genotype (Table 1).
Considering the patient’s previous unsuccessful trials of non-opioid
treatments (e.g., nonsteroidal anti-inflammatory drugs, skeletal muscle
relaxants), the clinical pharmacist recommended that the physician
consider an alternative opioid such as oxymorphone, hydromorphone, or
morphine, which are not metabolized by the CYP2D6 drug-metabolizing
enzyme. After her physician changed the opioid from oxycodone to
hydromorphone 2mg four to six times per day as needed, the patient’s
pain control improved significantly.
Importantly, the dose of hydromorphone was established as if the patient
was opioid naïve, since metabolic transformation of oxycodone into
oxymorphone was impaired due to genetic polymorphisms, drug-drug
interactions and drug-drug-gene interactions. A direct dose calculation
using morphine milligram equivalent dose algorithms was not applied,
considering that the dose of oxycodone was increased up to 60mg per day.