Known as pharmacogenetics, this form of precision medicine enables doctors to prescribe codeine only after genetic testing shows the medication will be safe and effective for that person.
“Having sickle cell and trying not to have a pain crisis is always on your mind, 24/7,” says Justin, now 22. “When you do anything, the first thing you think is, ‘Do I have my medicine with me?’ More times than not, the codeine helped.”
St. Jude has long been a leader in pharmacogenetics, the study of how a person’s genes influence which medications and doses will work best or may cause dangerous complications. Research has shown that about half of all hospitalized patients each year may receive drugs that, because of the recipients’ genetic makeup, could lead to serious side effects.
For more than two decades, pharmacogenetics has guided the use of chemotherapy in St. Jude patients treated for leukemia. The hospital is one of only a handful of institutions to offer pharmacogenetics testing to patients as standard care.
Since 2011, all new St. Jude patients have been screened for variations in 230 genes, including one called CYP2D6. This gene plays a pivotal role in how patients respond to codeine. The screening tests also determine responses to other drugs. These include certain chemotherapy agents as well as medications for nausea, depression and infections.
Codeine’s widespread use in pediatric patients has been questioned in recent years. Nationwide, several children who received it for post-surgical pain relief died. These deaths were later linked to CYP2D6 variations. After a warning by the U.S. Food and Drug Administration, some hospitals suggested ending all codeine use in children. Several pediatric hospitals removed the medication from their list of approved drugs.
But St. Jude is using personalized medicine to identify patients most likely to benefit from the drug, while avoiding codeine use in patients who are likely to experience side effects. Clinicians make sure codeine is given only to children whose genes indicate it will likely be safe and effective. About 12 percent of the general population carries CYP2D6 variants that drastically alter how their bodies process codeine.