MDElliottMD/Sandbox/CYP2C9: Difference between revisions

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== Function and substrate spectrum ==

CYP2C9 catalyzes hydroxylation, epoxidation, and N- and O-dealkylation across a substrate spectrum that, while narrower than CYP3A4's, contains a striking concentration of medicines with narrow therapeutic windows and well-defined dose-response toxicities. ~~Major clinical~~ substrates ~~include~~:

CYP2C9 catalyzes hydroxylation, epoxidation, and N- and O-dealkylation across a substrate spectrum that, while narrower than CYP3A4's, contains a striking concentration of medicines with narrow therapeutic windows and well-defined dose-response toxicities. The combination of warfarin and phenytoin alone, both of which are major CYP2C9 substrates with narrow therapeutic windows, accounts for a substantial share of the inpatient pharmacogenomic-testing case that has been built around this enzyme over the last two decades.<ref name="zanger2013">Zanger UM, Schwab M. Cytochrome P450 enzymes in drug metabolism: regulation of gene expression, enzyme activities, and impact of genetic variation. ''Pharmacology and Therapeutics''. 2013 Apr;138(1):103-141. PMID: 23333322.</ref>

* '''[[Warfarin|Warfarin]]''' (specifically the ~~S-enantiomer, which is three to five times more potent than R-warfarin and is the dominant determinant of the anticoagulant effect).~~

The table below collects the clinically important CYP2C9 substrates by therapeutic class, with each entry tagged by the contribution CYP2C9 makes to overall clearance: '''major''' (CYP2C9 is the predominant route; genotype-modulated and inhibitor-modulated interactions are clinically expected), '''moderate''' (CYP2C9 contributes meaningfully but other routes carry comparable load), and '''minor''' (CYP2C9 contributes but other pathways dominate). The list is curated for clinical relevance and is not exhaustive; see [[#Comprehensive substrate and interaction tables|Comprehensive substrate and interaction tables]] below for the authoritative maintained resources.

* '''[[Phenytoin|Phenytoin]]''', whose nonlinear pharmacokinetics make small changes in clearance produce large changes in plasma concentration and toxicity. The major hydroxylation step is CYP2C9~~-mediated~~, with ~~a minor CYP2C19~~ contribution.

* Several '''~~sulfonylureas~~'~~'': [[Glipizide|glipizide]], [[Glyburide|glyburide]]~~ (~~glibenclamide~~), ~~[[Glimepiride|glimepiride]], and the historical tolbutamide (which was the original probe substrate for the enzyme).~~

* '''~~Angiotensin-receptor blockers~~'''~~: [[Losartan|losartan]] is activated by~~ CYP2C9 ~~to its more potent metabolite E-3174; valsartan, irbesartan~~, and ~~candesartan also have CYP2C9 components.~~

* '''~~Fluvastatin~~''' (~~the only statin metabolized substantially by~~ CYP2C9 ~~rather than CYP3A4~~).

* A long list ~~of other agents at smaller scale, including~~ [[~~Sildenafil~~|~~sildenafil~~]]~~, [[Bosentan|bosentan]], and~~ the ~~modern direct oral anticoagulant components in mixed-metabolism pathways~~.

The ~~combination~~ of warfarin and ~~phenytoin alone, both~~ of ~~which are~~ CYP2C9 ~~substrates with narrow therapeutic windows~~, ~~accounts~~ for ~~a substantial share of~~ the ~~inpatient pharmacogenomic~~-~~testing case that has been built around this enzyme over~~ the ~~last two decades~~.

{| class="wikitable sortable"

! Substrate !! Therapeutic class !! CYP2C9 contribution !! Clinical notes

|-

| [[Acenocoumarol]] || Anticoagulant || major || Coumarin anticoagulant; reduced-function CYP2C9 alleles reduce dose requirement and raise bleeding risk, as with warfarin.

|-

| [[Bosentan]] || Endothelin-receptor antagonist || major || CYP2C9 and CYP3A4 dual metabolism; auto-induces CYP2C9 and CYP3A4 over the first weeks of therapy.

|-

| [[Candesartan]] || Angiotensin-receptor blocker || minor || Mostly cleared unchanged renally; CYP2C9 contribution is small.

|-

| [[Celecoxib]] || NSAID (COX-2 selective) || major || CPIC recommends dose reduction in CYP2C9 poor and intermediate metabolizers.

|-

| [[Cyclophosphamide]] || Antineoplastic (alkylating) || partial || Bioactivation to 4-hydroxycyclophosphamide is multi-CYP (CYP2B6 dominant, CYP2C9 and CYP3A4 contributing).

|-

| [[Diclofenac]] || NSAID || major || A canonical CYP2C9 probe substrate in research pharmacology.

|-

| [[Dronabinol]] || Cannabinoid (synthetic Δ9-THC) || moderate || Mixed CYP2C9 and CYP3A4 metabolism; CYP2C9 inhibition raises plasma THC.

|-

| [[Fluoxetine]] || SSRI antidepressant || partial || S-enantiomer is partly CYP2C9-cleared; fluoxetine is itself a moderate CYP2C9 inhibitor (see Inhibitors).

|-

| [[Flurbiprofen]] || NSAID || major || CPIC dose-reduction guidance in CYP2C9 PM/IM.

|-

| [[Fluvastatin]] || Statin (HMG-CoA reductase inhibitor) || major || The only statin metabolized predominantly by CYP2C9 rather than CYP3A4; CYP2C9 poor metabolizers have higher plasma exposures and higher rhabdomyolysis risk.

|-

| [[Glimepiride]] || Sulfonylurea (oral hypoglycaemic) || major || Hypoglycaemia risk raised in CYP2C9 PM/IM.

|-

| [[Glipizide]] || Sulfonylurea || major || Same pattern as glimepiride.

|-

| [[Glyburide]] || Sulfonylurea (glibenclamide) || major || Same pattern as glimepiride.

|-

| [[Ibuprofen]] || NSAID || major || CPIC dose-reduction guidance in CYP2C9 PM/IM.

|-

| [[Indomethacin]] || NSAID || moderate || Both CYP2C9 and conjugation routes; less affected by CYP2C9 genotype than ibuprofen or celecoxib.

|-

| [[Irbesartan]] || Angiotensin-receptor blocker || major || CYP2C9 is the predominant oxidative route.

|-

| [[Lornoxicam]] || NSAID || major || CPIC dose-reduction guidance in CYP2C9 PM/IM.

|-

| [[Losartan]] || Angiotensin-receptor blocker (prodrug) || major || '''Activation reaction''', not inactivation: CYP2C9 converts losartan to E-3174, the active metabolite responsible for most of the antihypertensive effect. CYP2C9 poor metabolizers may have reduced antihypertensive response.

|-

| [[Meloxicam]] || NSAID || major || CPIC dose-reduction guidance in CYP2C9 PM/IM; long half-life magnifies the accumulation problem in poor metabolizers.

|-

| [[Naproxen]] || NSAID || moderate || Less CYP2C9-dependent than diclofenac or ibuprofen; conjugation contributes substantially.

|-

| [[Nateglinide]] || Meglitinide (oral hypoglycaemic) || moderate || Mixed CYP2C9 and CYP3A4.

|-

| [[Phenprocoumon]] || Anticoagulant (coumarin) || major || Same anticoagulant-class CYP2C9 dependence as warfarin and acenocoumarol; more relevant in European practice than US.

|-

| [[Phenytoin]] || Antiepileptic || major || CPIC dose-reduction guidance in CYP2C9 PM/IM; nonlinear pharmacokinetics make small clearance changes produce large concentration changes. Minor CYP2C19 contribution.

|-

| [[Piroxicam]] || NSAID || major || CPIC dose-reduction guidance in CYP2C9 PM/IM; long half-life.

|-

| [[Rosiglitazone]] || Thiazolidinedione (oral hypoglycaemic) || moderate || Mixed CYP2C8 and CYP2C9.

|-

| [[Sildenafil]] || PDE5 inhibitor || minor || CYP3A4 is the dominant clearance route; CYP2C9 contribution is real but small.

|-

| [[Sulfamethoxazole]] || Sulfonamide antibiotic || moderate || Self-metabolised partly by CYP2C9; sulfamethoxazole is also a moderate CYP2C9 inhibitor (the source of trimethoprim-sulfamethoxazole interactions with warfarin).

|-

| [[Tamoxifen]] || Anti-estrogen (breast cancer) || minor || 4-hydroxylation pathway is partly CYP2C9; the major activation pathway (to endoxifen) is CYP2D6, dominantly.

|-

| [[Tenoxicam]] || NSAID || major || CPIC dose-reduction guidance in CYP2C9 PM/IM; long half-life.

|-

| [[THC|Tetrahydrocannabinol (Δ9-THC)]] || Cannabinoid || moderate || See cannabinoid-pharmacology page; mixed CYP2C9 + CYP3A4 metabolism.

|-

| [[Tolbutamide]] || Sulfonylurea (historical) || major || The original probe substrate for CYP2C9 in research pharmacology; rarely prescribed clinically today but central to the historical literature.

|-

| [[Torsemide]] || Loop diuretic || major || CYP2C9 PM status raises plasma torsemide and prolongs diuretic effect.

|-

| [[Valproic acid]] || Antiepileptic, mood stabilizer || minor || Predominantly cleared by glucuronidation and beta-oxidation; CYP2C9 contribution is small.

|-

| [[Valsartan]] || Angiotensin-receptor blocker || minor || Cleared mostly unchanged in bile; CYP2C9 contribution is small.

|-

| [[Voriconazole]] || Triazole antifungal || moderate || Mixed CYP2C19 (major), CYP2C9, and CYP3A4; CYP2C19 genotype dominates the clinical pharmacogenomics story for voriconazole, but CYP2C9 contributes.

|-

| '''[[Warfarin]]''' || Anticoagulant || major || '''Canonical CYP2C9 substrate.''' CYP2C9 clears the more potent S-enantiomer. CPIC warfarin guideline integrates CYP2C9 with [[Enzyme:VKORC1|VKORC1]] for dose-prediction.

|-

| [[Zafirlukast]] || Leukotriene-receptor antagonist || moderate || Also a CYP2C9 inhibitor (significant warfarin interaction).

|}

== Phenotype categories ==

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The original clinical-genetic observation linking CYP2C9 polymorphism to warfarin dose requirements was the 1999 ''Lancet'' paper by Aithal and colleagues, who showed in a Newcastle cohort that patients with reduced-function CYP2C9 alleles required lower warfarin doses and had a higher risk of bleeding complications than wild-type patients.<ref name="aithal1999">Aithal GP, Day CP, Kesteven PJ, Daly AK. Association of polymorphisms in the cytochrome P450 CYP2C9 with warfarin dose requirement and risk of bleeding complications. ''Lancet''. 1999 Feb 27;353(9154):717-719. PMID: 10073515.</ref> That paper opened the modern era of CYP2C9 pharmacogenomics; the CPIC guidelines above are its lineal descendants.

== Comprehensive substrate and interaction tables ==

The substrate and interaction tables on this page are curated for clinical relevance, not for completeness. Three authoritative external resources maintain comprehensive lists of CYP2C9 substrates, inhibitors, and inducers, and the wiki recommends them to any reader who needs an exhaustive look-up:

* '''Flockhart Cytochrome P450 Drug Interaction Table''', maintained by the Department of Medicine at Indiana University School of Medicine. The most widely cited clinical-reference cytochrome P450 table; substrate-, inhibitor-, and inducer-tiered, updated regularly. Available at https://drug-interactions.medicine.iu.edu/.

* '''U.S. Food and Drug Administration Drug Development and Drug Interactions Table''', the regulatory-grade list FDA uses for labeling and clinical-trial design decisions. Smaller than Flockhart but every entry is FDA-vetted. Available via the FDA Center for Drug Evaluation and Research clinical drug interaction page.

* '''PharmGKB''', the pharmacogenomics knowledge base hosted at Stanford University; the CYP2C9 gene page indexes substrate-, inhibitor-, and inducer-relationships with their underlying primary literature, and links each gene-drug pair to the CPIC dosing guideline where one exists.<ref name="pharmgkb2021">Whirl-Carrillo M, Huddart R, Gong L, Sangkuhl K, Thorn CF, Whaley R, Klein TE. An Evidence-Based Framework for Evaluating Pharmacogenomics Knowledge for Personalized Medicine. ''Clinical Pharmacology and Therapeutics''. 2021 Sep;110(3):563-572. PMID: 34216021.</ref> Available at https://www.pharmgkb.org/.

For a comprehensive review of CYP2C9 (and the rest of the human cytochrome P450 family) covering regulation, polymorphism, and substrate spectrum in detail, the Zanger and Schwab 2013 review in ''Pharmacology and Therapeutics'' remains the standard reference.<ref name="zanger2013" />

== See also ==

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