Pharmacotherapy continues to be central to the treatment of many psychiatric illnesses, with antipsychotic and antidepressant medications constituting the primary treatment for the majority of disorders. However these medications frequently produce sub-optimal results; many patients do not experience improvements in their symptoms and many experience intolerable side effects.
The ability of an individual to metabolize medications influences plasma drug levels. Two cytochrome P450 enzymes, CYP2D6 and CYP2C19, are responsible for the metabolism of most antipsychotic and antidepressant medications. Patients with impaired activity of these enzymes, called “poor metabolizers”, are more likely to experience higher drug levels and are at an increased risk of experiencing side effects. Alternatively, patients with increased activity of these enzymes, called “ultrarapid metabolizers”, may experience low plasma levels of medication and standard dosages of medication may not achieve a therapeutic effect.
The Pharmacogenetics Research Clinic at CAMH is an exciting new initiative and one of the first of its kind. Here patients are currently being genotyped to determine their metabolizer status for the CYP2D6 and CYP2C19 enzymes. Information about the metabolic capabilities of each patient is passed on to their physician who can then select medications that are unlikely to induce side effects and alter dosages if necessary. This pharmacogenetic testing may help to personalize treatment for patients, minimizing trial-and-error prescribing and reducing the amount of time before patients see benefits from pharmacotherapy.
For more information on CYP enzymes substrates, inhibitors and inducers, please see this link.
Information for Physicians: (PDF 191kB)
Information for Patients: (PDF 112kB)