This drug gene interaction (DGI) pertains to the interaction between the cytochrome P450 2C19 (CYP2C19) gene and citalopram. Citalopram (brand name Celexa®) belongs to a class of drugs known as selective serotonin re-uptake inhibitors (SSRIs). SSRIs work by blocking the re-uptake of serotonin. The increase in serotonin levels has been linked to the management of depression, social anxiety disorder, obsessive-compulsive disorder, panic disorder, premenstrual dysphoric disorder, and post-traumatic stress disorder among other conditions. Extensive literature indicates that patients with specific genetic differences in the CYP2C19 gene may require dose adjustments of citalopram or an alternative medication in order to achieve therapeutic benefits or to avoid side effects.
Information presented on this page is based on evidence provided by the Clinical Pharmacogenomics Implementation Consortium (CPIC®). CPIC provides peer-reviewed, updated, evidence-based, and freely accessible guidelines for implementing pharmacogenomic results into actionable prescribing decisions for providers. CPIC guidelines include standardized terminology and a systematic grading of evidence and clinical recommendations published in a leading journal (Clinical Pharmacology and Therapeutics).
The CYP2C19 (sounds like “sip-2-see-19”) gene encodes the CYP2C19 enzyme, which is a member of the cytochrome P450 enzyme family. There are different CYP2C19 gene versions, or variants, and each has a different effect on how well citalopram is metabolized in the body. Some variants reduce or eliminate the function of the CYP2C19 enzyme, while other variants either do not change or increase the function of the CYP2C19 enzyme. Different ‘metabolizer statuses’ are assigned to patients depending on their genetic information (genotype).
See chart below for a description of each metabolizer status and any implications for treatment.
CYP2C19 metabolizer status
Implication for citalopram
The patient’s reported genotype corresponds to a phenotype (i.e., metabolizer status). To see an interpretation table assigning metabolizer status by genetic variant, click here to visit CPIC and scroll down to click and download “CYP2C19_Diplotype_Phenotype_Table”.
Citalopram is a medicine used to manage several different conditions and your genes can affect how well the drug works. CPIC updates guidelines on how to best use these genetic results to support patient care and has published its current interpretations here.
According to the FDA label, the maximum recommended dose of citalopram is 20 mg/day for CYP2C19 poor metabolizers.
Genotyping for CYP2C19 was performed within a certified DNA laboratory at Vanderbilt University Medical Center that is in full compliance with all guidelines established by the government as regulated by the Centers for Medicare & Medicaid Services under the Clinical Laboratory Improvement Act of 1988. This validated clinical laboratory developed test is carried out with strict adherence to protocols outlined by the College of American Pathology. The performance of the assay is closely monitored and the accuracy of the results is determined to be > 99%.
Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2D6 and CYP2C19 Genotypes and Dosing of Selective Serotonin Reuptake Inhibitors
This link will take you to the main page on the CPIC website relating to CYP2D6, CYP2C19 and SSRIs. On the site, you will find links to the main guideline publication and all supplementary information including a table that reports variant frequencies across different races/ethnic groups, a table that defines genetic variants, and a table that provides a phenotype interpretation (i.e. metabolizer status). Additionally, examples of point of care clinical decision support can be found at the bottom of the page.
Please note that additional drugs may have CYP2C19 interactions. For more information on drug-gene interactions, please use the search feature on the CPIC website.