“The CYP2C19 enzyme plays a role in the processing or metabolizing of **at least 10 percent of commonly prescribed drugs**, including a drug called **clopidogrel** (also known as Plavix).” It adds: “Other drugs that are affected by *CYP2C19* gene polymorphisms include **proton pump inhibitors**, used to treat stomach ulcers and other conditions; **antidepressants**, used to treat psychiatric disorders; anticonvulsants… hypnotics and sedatives… antimalarial drugs… and antiretroviral drugs.”

CYP2C19 is involved in the metabolism of several important classes of drugs, including proton pump inhibitors, certain antidepressants, benzodiazepines, antiepileptics, and the antiplatelet agent clopidogrel. It has been estimated that CYP2C19 is responsible for the metabolism of approximately 10% of commonly prescribed drugs. Substrates include clopidogrel, some selective serotonin reuptake inhibitors (SSRIs), many proton pump inhibitors, and certain antifungal agents such as voriconazole.

Voriconazole, a triazole antifungal agent, demonstrates wide interpatient variability in serum concentrations, due in part to variant CYP2C19 alleles. Voriconazole is metabolized in vitro predominantly by CYP2C19 with contribution from CYP3A and CYP2C9. The metabolism of proton pump inhibitors, and variant CYP2C19 alleles have been implicated in the development and progression of gastritis, peptic ulcer disease, and gastric carcinoma. In addition, no function CYP2C19 alleles have reproducibly been associated with lower active metabolite levels of clopidogrel and increased adverse cardiovascular event rates among patients with clopidogrel-treated acute coronary syndrome undergoing percutaneous coronary intervention. CYP2C19 and CYP2D6 are involved in the metabolism of tricyclic antidepressants.

Clopidogrel is a prodrug that requires hepatic biotransformation via cytochrome P450 (CYP) enzymes to an active thiol metabolite. CYP2C19 is one of the major enzymes involved in the two-step bioactivation of clopidogrel. Individuals who carry one or two no function CYP2C19 alleles have reduced formation of the active metabolite and decreased inhibition of platelet aggregation, which has been associated with adverse cardiovascular events in clopidogrel-treated patients.

One overview states: “The **CYP2C19 enzyme plays a role in the metabolism of approximately 10% of commonly prescribed drugs** [74]. This includes frequently used psychiatric drugs and categories such as escitalopram and citalopram, where it serves as the principal metabolic enzyme; sertraline… and tricyclic antidepressants (TCAs).” Another section notes that medications metabolized by CYP2C19 include “omeprazole, pantoprazole, **citalopram, sertraline**…”.

Voriconazole undergoes extensive hepatic metabolism, which is predominantly mediated by the cytochrome P450 (CYP) 2C19 enzyme and to a lesser extent by CYP3A4 and CYP2C9. CYP2C19 genetic polymorphisms significantly affect voriconazole metabolism and pharmacokinetics, causing marked interindividual variability in voriconazole exposure. Individuals who are CYP2C19 ultrarapid metabolizers have decreased trough voriconazole concentrations, whereas poor metabolizers have increased trough concentrations and are at increased risk of adverse drug events.

This 2023 review notes that “CYP2C19 is a member of the CYP2C subfamily of cytochromes which are involved in the metabolism of a range of clinically important compounds, such as anticoagulants, **proton pump inhibitors (PPIs)**, benzodiazepines, anticonvulsants, and **tricyclic antidepressants**.” A table lists drugs **primarily metabolized by CYP2C19**, including PPIs (lansoprazole, pantoprazole, omeprazole/esomeprazole), the antifungal **voriconazole**, cardiovascular agent **clopidogrel**, and numerous **antidepressants (SSRIs and TCAs)** such as citalopram, escitalopram, sertraline, fluoxetine, imipramine, and others.

Proton pump inhibitors (PPIs) such as omeprazole, lansoprazole, pantoprazole, and esomeprazole are extensively metabolized in the liver by the cytochrome P450 enzyme system. CYP2C19 is the principal enzyme responsible for the metabolism of many PPIs. Genetic polymorphisms in CYP2C19 significantly influence the pharmacokinetics and pharmacodynamics of PPIs, with poor metabolizers exhibiting higher plasma concentrations and prolonged acid suppression.

In vitro analyses identified CYP2C19 as the primary enzyme mediating voriconazole metabolism, with CYP3A4/5 playing a secondary role. In vivo, CYP2C19 polymorphisms and noncompliance significantly influenced voriconazole exposure. Steady-state voriconazole area under the concentration-time curve was significantly associated with CYP2C19 genotypes, with more than a ninefold reduction in exposure in CYP2C19*17/*17 compared to CYP2C19*2/*2 carriers.

Voriconazole, a first line agent for the treatment of invasive fungal infections, is metabolized by CYP2C19. Voriconazole undergoes extensive hepatic metabolism, which is predominantly mediated by the cytochrome P450 (CYP) 2C19 enzyme. Our findings indicate that adults with the CYP2C19 rapid metabolizer or ultrarapid metabolizer phenotype are more likely to have subtherapeutic concentrations with weight-based voriconazole dosing, supporting potential clinical utility of CYP2C19 genotype-guided voriconazole dosing.

In the background, the article describes CYP2C19 as “the main enzyme involved in bioactivation and metabolism of commonly prescribed medications, including those with a high risk of clinically significant drug–drug interactions.” This places CYP2C19 among key enzymes for a broad range of **commonly prescribed medications**, although it does not give a specific percentage of all drugs.

The CPIC guideline introduction states: “**CYP2C19 is a major enzyme responsible for the metabolism of many commonly prescribed proton pump inhibitors (PPIs)** including omeprazole, esomeprazole, lansoprazole, pantoprazole and others.” It further explains that CYP2C19 genotype influences exposure to these PPIs, and provides dosing recommendations based on metabolizer phenotype.

The guideline notes that “Clopidogrel is a prodrug that requires biotransformation predominantly by **CYP2C19 to an active thiol metabolite** that inhibits platelet aggregation.” It also summarises that **genetic variation in CYP2C19** alters active metabolite exposure and platelet response, leading CPIC to issue dosing and therapy recommendations for clopidogrel based on CYP2C19 metabolizer status.

The CPIC voriconazole guideline states: “Voriconazole is primarily metabolized by **CYP2C19**, with contributions from CYP2C9 and CYP3A4.” It explains that “**CYP2C19 poor metabolizers have higher voriconazole exposure** and are at increased risk of adverse effects, whereas ultrarapid metabolizers have lower concentrations and increased risk of therapeutic failure,” and therefore recommends dose modifications or alternative therapy based on CYP2C19 genotype.

Several selective serotonin reuptake inhibitors (SSRIs), including citalopram, escitalopram, and sertraline, are metabolized by CYP2C19 among other cytochrome P450 enzymes. CYP2C19 genetic variation can alter plasma concentrations of these antidepressants, particularly for citalopram and escitalopram, and has been incorporated into dosing recommendations in pharmacogenetic guidelines.

Voriconazole, a first-line agent for the treatment of invasive fungal infections, is mainly metabolized by human cytochrome P450 (CYP) 2C19. Proton pump inhibitors (PPIs) are able to influence voriconazole metabolism by competitive inhibition against CYP2C19. A multicenter prospective study in adults has demonstrated increased voriconazole exposure with omeprazole due to an inhibition of CYP2C19.

The PharmaGKB summary notes: “The **CYP2C19 enzyme contributes to the metabolism of a large number of clinically relevant drugs and drug classes such as antidepressants, benzodiazepines, mephenytoin, proton pump inhibitors (PPIs), and the antiplatelet prodrug clopidogrel**.” It further states that most PPIs are “predominantly metabolized by CYP2C19” and that CYP2C19 is involved in metabolism of tricyclic **antidepressants** (imipramine, amitriptyline, trimipramine, clomipramine, nortriptyline).

Reviewing pharmacogenetics of antidepressant metabolism, the article notes that among CYP enzymes “**CYP2D6 and CYP2C19 are the most important for the oxidative metabolism of many tricyclic antidepressants and some SSRIs**,” and that genetic polymorphisms in these enzymes affect plasma concentrations and response. This supports the role of CYP2C19 in the metabolism of a range of antidepressants.

Voriconazole undergoes N-oxidative metabolism in the liver, predominantly by the CYP2C19 isoenzyme and to a lesser extent by CYP2C9 and CYP3A4. Voriconazole N-oxide is the major metabolite in the circulation and accounts for more than 70% of the circulating metabolites in plasma. Previous in vitro studies have shown that voriconazole N-oxide has inhibitory effects on CYP2C19 and CYP3A4 activities.

The NHS Knowledge Hub describes *CYP2C19* as: “a very important gene in the field of pharmacogenomics. It encodes a cytochrome P450 enzyme that **metabolises many commonly prescribed medicines, including antidepressants, proton pump inhibitors and clopidogrel**, an antiplatelet drug.” It further notes that CPIC has published genotype‑based guidelines for “clopidogrel; **proton pump inhibitors; selective serotonin reuptake inhibitors (SSRIs); tricyclic antidepressants; and voriconazole**.”

The overview lists examples: “Medications that are **metabolized by CYP2C19 include omeprazole, pantoprazole, citalopram, sertraline, and etravirine**.” It also notes that “Nearly 500 drugs are *CYP2C19*-related, with 281 acting as substrates (151 major, 130 minor), 263 as inhibitors… and 23 as inducers of the CYP2C19 enzyme.” This underscores the large number of drugs for which CYP2C19 plays some role in metabolism or interaction.

Jeen Health’s educational article states: “**CYP2C19 encodes a liver enzyme that metabolises approximately 10% of commonly prescribed drugs, including the antiplatelet medication clopidogrel.**” It adds: “Research suggests that CYP2C19 processes **at least one in ten commonly prescribed medications**, making it clinically significant for personalised medicine approaches… Beyond clopidogrel, CYP2C19 metabolises **proton pump inhibitors**, certain **antidepressants**, antiepileptic drugs, and various other therapeutic agents.”

Voriconazole, a first-line agent for the treatment of invasive fungal infections, is mainly metabolized by cytochrome P450 (CYP) 2C19. Concomitant use of drugs that inhibit or induce CYP2C19 can significantly alter voriconazole exposure, contributing to the wide interpatient variability observed with this drug.

St. Jude explains that “CYP2C19 is an enzyme that is responsible for **breaking down (metabolizing) several of the drugs that are commonly used today**.” It adds: “Some medications, such as **clopidogrel**, require activation by CYP2C19 in order for the medication to be effective. Other drugs, such as **voriconazole and antidepressants (e.g., amitriptyline and sertraline), are metabolized** to forms that are not active and are more easily eliminated from the body.”

An overview section notes: “P450 cytochromes **CYP2D6 and CYP2C19 are heavily involved in the metabolism of commonly prescribed antidepressants**.” In the same topic page, CYP2C19 is listed among six specific genes whose enzymes “play a particularly crucial role in pharmacogenetics since the enzymes they encode facilitate phase I metabolism for **over 90% of frequently prescribed medications**,” indicating that CYP2C19 contributes to the metabolism of a substantial fraction of commonly used drugs together with other CYPs.

DrugBank’s category “Cytochrome P-450 CYP2C19 Substrates” lists numerous drugs where CYP2C19 is involved in metabolism. The list includes the proton pump inhibitor **omeprazole** (“A medication used to treat heartburn associated with GERD”), the SSRI **citalopram** (“A selective serotonin reuptake inhibitor (SSRI) used in the treatment of depression”), and many other medications, showing that CYP2C19 has a wide substrate range among commonly prescribed therapies.

The page states: “**CYP2C19 is a liver enzyme that acts on at least 10% of drugs in current clinical use**, most notably the antiplatelet treatment **clopidogrel** (Plavix), drugs that treat pain associated with ulcers, such as **omeprazole**, antiseizure drugs such as mephenytoin, the antimalarial proguanil, and the anxiolytic diazepam.” It also notes: “CYP2C19 is involved in processing or metabolizing **at least 10% of commonly prescribed drugs**.”

The white paper states: “Cytochrome P450 2C19 (CYP2C19) **metabolizes 5% of the prescription drugs in use today**.” It also notes that, “Cytochrome P450 enzyme 2C19 (CYP2C19) **metabolizes many clinically important drugs including proton pump inhibitors, antidepressants, the antiplatelet drug clopidogrel, and the antifungal voriconazole**.” This provides an alternative estimate (5%) to other sources that mention 10%.

This explainer notes that “CYP2C19 is a cytochrome P450 enzyme that your liver uses to **break down a wide range of medications, including clopidogrel (Plavix)… proton pump inhibitors like omeprazole; and several antidepressants including sertraline and escitalopram**.” It adds that it “controls metabolism of clopidogrel, PPIs, and many psychiatric medications,” emphasizing CYP2C19’s role in these drug classes, though it does not provide a percentage of all prescribed drugs.

Across pharmacology and pharmacogenomics texts, CYP2C19 is routinely cited as metabolizing on the order of **5–10% of drugs in current clinical use**, alongside other major CYP enzymes such as CYP3A4, CYP2D6, and CYP2C9. Estimates vary by author and by how “commonly prescribed drugs” are defined, which explains why some documents (e.g., industry white papers) state 5% while genetics summaries from NIH and reference-style sources state **“at least 10% of commonly prescribed drugs.”**