{ "id": "ep0r0nxf4h", "slug": "coumachlor", "title": "Coumachlor", "updated": "2026-10-21", "topic_path": [ { "id": "life", "label": "Life and health", "api_url": "https://www.edgepedia.org/api/v1/topics/life" }, { "id": "life.production", "label": "Applied biology and nonhuman health", "api_url": "https://www.edgepedia.org/api/v1/topics/life.production" }, { "id": "life.production.plant_health", "label": "Plant disease and plant protection", "api_url": "https://www.edgepedia.org/api/v1/topics/life.production.plant_health" }, { "id": "life.production.plant_health.pesticides", "label": "Pesticides", "api_url": "https://www.edgepedia.org/api/v1/topics/life.production.plant_health.pesticides" }, { "id": "life.production.plant_health.pesticides.rodenticides", "label": "Rodenticides", "api_url": "https://www.edgepedia.org/api/v1/topics/life.production.plant_health.pesticides.rodenticides" } ], "geo": [ { "id": "geo.us.t1946.life.production.plant_health.pesticides", "label": "United States · 1946 to 2000: Pesticides", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.us.t1946.life.production.plant_health.pesticides", "path": [ { "id": "geo.us", "label": "United States", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.us" }, { "id": "geo.us.t1946", "label": "United States · 1946 to 2000", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.us.t1946" }, { "id": "geo.us.t1946.life", "label": "Life and health", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.us.t1946.life" }, { "id": "geo.us.t1946.life.production", "label": "Applied biology and nonhuman health", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.us.t1946.life.production" }, { "id": "geo.us.t1946.life.production.plant_health", "label": "Plant disease and plant protection", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.us.t1946.life.production.plant_health" }, { "id": "geo.us.t1946.life.production.plant_health.pesticides", "label": "Pesticides", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.us.t1946.life.production.plant_health.pesticides" } ] } ], "excerpt": "Coumachlor (CAS 81-82-3, p-chlorowarfarin, Tomorin) is a first-generation hydroxycoumarin anticoagulant rodenticide and warfarin analog, a vitamin K antagonist, historically used in Canada, France, Germany, and Malaya and now largely unregistered.", "snippet": "Coumachlor (CAS 81-82-3, p-chlorowarfarin, Tomorin) is a first-generation hydroxycoumarin anticoagulant rodenticide and warfarin analog, a vitamin K antagonist, historically used in Canada, France, Germany, and Malaya and now largely unregistered.", "node": "life.production.plant_health.pesticides.rodenticides", "markdown": "# Coumachlor\n\n**Coumachlor** (CAS 81-82-3) is a first-generation hydroxycoumarin anticoagulant rodenticide, a structural analog of warfarin in which a chlorine atom replaces one hydrogen on the phenyl ring. Its CAS name is 3-[1-(4-chlorophenyl)-3-oxobutyl]-4-hydroxy-2H-1-benzopyran-2-one, and its molecular formula is C\\(_{19}\\)H\\(_{15}\\)ClO\\(_{4}\\) with a molecular weight of 342.77.[1](https://www.drugfuture.com/chemdata/coumachlor.html) • [2](https://www.inchem.org/documents/ehc/ehc/ehc175.htm) It is a vitamin K antagonist that kills rodents by interfering with blood coagulation.[3](https://www.medchemexpress.com/coumachlor.html)\n\n| Key fact | Detail |\n|---|---|\n| Chemical identity | CAS 81-82-3; C\\(_{19}\\)H\\(_{15}\\)ClO\\(_{4}\\); molecular weight 342.77; CAS name 3-[1-(4-chlorophenyl)-3-oxobutyl]-4-hydroxy-2H-1-benzopyran-2-one[1](https://www.drugfuture.com/chemdata/coumachlor.html) |\n| Class | First-generation hydroxycoumarin anticoagulant rodenticide, alongside coumafuryl, coumatetralyl, and warfarin[2](https://www.inchem.org/documents/ehc/ehc/ehc175.htm) • [4](https://www.pharmaco.vet.ku.ac.th/pdf_file/Pesticide_20161020.pdf) |\n| Other names | p-Chlorowarfarin, Tomorin, Rival, manufacturers' code G-21133[5](https://precision.fda.gov/uniisearch/srs/unii/UCD8XZW42P) • [1](https://www.drugfuture.com/chemdata/coumachlor.html) |\n| Mechanism | Inhibits hepatic vitamin K1 epoxide reductase, reducing regeneration of active vitamin K and preventing the activation of vitamin K-dependent clotting factors, including prothrombin[6](https://hero.epa.gov/reference/1360481/) • [18](https://pmc.ncbi.nlm.nih.gov/articles/PMC6996659/) |\n| Field performance | In comparative trials on common rats, coumachlor baits at 0.005% killed 2 of 11 and 4 of 11 animals, against near-complete kills with warfarin at the same concentration[7](https://www.cambridge.org/core/services/aop-cambridge-core/content/view/94C9ACAF284DB31F911F41A635A7662D/S0022172400019975a.pdf/div-class-title-the-comparative-rodenticidal-efficiency-of-five-anti-coagulants-div.pdf) |\n| Regulatory status | Not registered as a plant protection product in Turkey following a final regulatory action banning it; no longer registered for use in California[8](https://www.pic.int/Portals/5/download.aspx?d=UNEP-FAO-RC-PUB-PicCircular-54.English.pdf) • [9](https://www.cdfa.ca.gov/plant/IPC/vertebrates/docs/vpcrac/reports/Assessing_some_potential_environmental_impaxts_from_agricultureal_anticoagulant_uses_copy.pdf) |\n\n## Chemistry and pharmacology\n\nCoumachlor belongs to the 4-hydroxycoumarin series of anticoagulants, a group derived from coumarin that also includes dicoumarol and warfarin.[6](https://hero.epa.gov/reference/1360481/) Like the other hydroxycoumarin rodenticides, it acts as a vitamin K antagonist: these compounds inhibit hepatic vitamin K1 epoxide reductase, the enzyme involved in the regeneration of active vitamin K, preventing activation of vitamin K-dependent clotting factors, including prothrombin, so blood fails to clot and the animal dies of hemorrhage.[6](https://hero.epa.gov/reference/1360481/) • [18](https://pmc.ncbi.nlm.nih.gov/articles/PMC6996659/) A 1953 study in *Acta Pharmacologica et Toxicologica* by H. Dam and E. Søndergaard compared its anticoagulant action with that of dicoumarol in chicks and rats.[10](https://pubmed.ncbi.nlm.nih.gov/13079850/)\n\nThe compound is a racemate, listed in chemical registries as the (±)-form of 3-(α-acetonyl-4-chlorobenzyl)-4-hydroxycoumarin, and it appears in the FDA's UNII inventory as an ingredient substance with the UNII code UCD8XZW42P.[5](https://precision.fda.gov/uniisearch/srs/unii/UCD8XZW42P)\n\n## Use as a rodenticide\n\nFirst-generation hydroxycoumarins, coumachlor among them, were introduced as rodenticides in the late 1940s.[2](https://www.inchem.org/documents/ehc/ehc/ehc175.htm) A WHO regional seminar document, citing Bentley (1966), lists coumachlor among the anticoagulants favored in Canada (as Rival and Coumachlor), France (with [chlorophacinone](https://www.edgepedia.org/chlorophacinone) and LM 83), Germany (with [coumatetralyl](https://www.edgepedia.org/coumatetralyl) and fumarin), and Malaya.[11](https://applications.emro.who.int/docs/EM_SEM_PH_EC_ASP_ROD_CTL_12_EN.pdf)\n\n**Comparative efficacy.** A published trial series on common rats measured mortality after three days of feeding on poisoned bait. Coumachlor performed poorly at low concentrations: at 0.005% bait it killed 2 of 11 rats in one series and 4 of 11 in another, and even at 0.05% it killed 2 of 11 and 6 of 12, with time-to-death stretching to 55–120 hours at the higher concentrations. The authors concluded that the results would appear to contra-indicate the use of coumachlor at 0.05% or less, since warfarin at 0.005% gave a nearly complete kill of rats that had fed exclusively on it for 96 hours.[7](https://www.cambridge.org/core/services/aop-cambridge-core/content/view/94C9ACAF284DB31F911F41A635A7662D/S0022172400019975a.pdf/div-class-title-the-comparative-rodenticidal-efficiency-of-five-anti-coagulants-div.pdf)\n\n## Regulatory status\n\nUnder the Rotterdam Convention's PIC Circular, Turkey reported a final regulatory action banning coumachlor as a pesticide, summarizing that coumachlor is not registered as a plant protection product in the country.[8](https://www.pic.int/Portals/5/download.aspx?d=UNEP-FAO-RC-PUB-PicCircular-54.English.pdf) In the United States, a California Department of Food and [Agriculture](https://www.edgepedia.org/agriculture) report notes that coumachlor is no longer registered for use in California, though the chemical was still tested for in wildlife monitoring.[9](https://www.cdfa.ca.gov/plant/IPC/vertebrates/docs/vpcrac/reports/Assessing_some_potential_environmental_impaxts_from_agricultureal_anticoagulant_uses_copy.pdf) In the European Union, coumachlor appears in ECHA's substance inventory (EC number 201-378-1) with regulatory obligations under REACH and related frameworks.[12](https://chemicalsinourlife.echa.europa.eu/sv/web/guest/substance-information/-/substanceinfo/100.001.254?_disssubsinfo_WAR_disssubsinfoportlet_substanceId=100.001.254)\n\n## Detection and monitoring\n\nModern analytical methods detect coumachlor alongside other anticoagulant rodenticides in biological samples. A validated serum method using quadratic calibration with 1/x weighting reported an instrument limit of detection of 0.05 ng/mL and a limit of quantification of 0.3 ng/mL in solvent for coumachlor, with a method limit of quantification of 2.5 ng/mL in serum.[13](https://academic.oup.com/view-large/406408876) An interlaboratory comparison of liver analysis by ultra-performance liquid chromatography with mass spectrometry measured coumachlor recoveries of 92 to 104 percent at spike levels from 130 to 2,000 ng/mL.[14](https://journals.sagepub.com/doi/10.1177/10406387231178558) A 2012 HPLC method with fluorimetric detection validated coumachlor among eight anticoagulant rodenticides and reported chromatograms of a cat liver and a bait that tested positive for coumachlor.[15](https://journals.sagepub.com/doi/full/10.1177/1040638711433354)\n\nIn food monitoring, the [European Food Safety Authority](https://www.edgepedia.org/european-food-safety-authority)'s 2017 scientific report on the 2015 EU coordinated program recorded 3,970 analyses for coumachlor in one country with zero quantifications above the limit of quantification, a quantification rate of 0.00 percent.[16](https://www.gastronomiaycia.com/wp-content/uploads/2017/04/Authority-2017-EFSA_Journal.pdf) A University of California study similarly reported that warfarin, chlorophacinone, and coumachlor were rarely detected in wildlife samples.[17](https://escholarship.org/content/qt7xf8b9kp/qt7xf8b9kp_noSplash_528a84be46174693b5cdba259c834397.pdf?t=nd83yc)\n\n## References\n\n1. [Coumachlor, DrugFuture chemical data sheet](https://www.drugfuture.com/chemdata/coumachlor.html)\n2. [Anticoagulant rodenticides, Environmental Health Criteria 175, WHO/IPCS (1995)](https://www.inchem.org/documents/ehc/ehc/ehc175.htm)\n3. [Coumachlor, MedChemExpress](https://www.medchemexpress.com/coumachlor.html)\n4. [Pesticide handbook, Faculty of Veterinary Science, Chulalongkorn University (Thai)](https://www.pharmaco.vet.ku.ac.th/pdf_file/Pesticide_20161020.pdf)\n5. [COUMACHLOR, FDA UNII record UCD8XZW42P](https://precision.fda.gov/uniisearch/srs/unii/UCD8XZW42P)\n6. [Peoples SA (1970). The pharmacology of rodenticides, Vertebrate Pest Conference](https://hero.epa.gov/reference/1360481/)\n7. [The comparative rodenticidal efficiency of five anti-coagulants, Cambridge Core](https://www.cambridge.org/core/services/aop-cambridge-core/content/view/94C9ACAF284DB31F911F41A635A7662D/S0022172400019975a.pdf/div-class-title-the-comparative-rodenticidal-efficiency-of-five-anti-coagulants-div.pdf)\n8. [PIC Circular LIV (54), December 2021, Rotterdam Convention](https://www.pic.int/Portals/5/download.aspx?d=UNEP-FAO-RC-PUB-PicCircular-54.English.pdf)\n9. [Assessing some potential environmental impacts from agricultural anticoagulant uses, California Department of Food and Agriculture](https://www.cdfa.ca.gov/plant/IPC/vertebrates/docs/vpcrac/reports/Assessing_some_potential_environmental_impaxts_from_agricultureal_anticoagulant_uses_copy.pdf)\n10. [Dam H, Søndergaard E (1953). Comparison of the anticoagulant action of coumachlor and dicoumarol in chicks and rats, Acta Pharmacol Toxicol 9(2):137–47](https://pubmed.ncbi.nlm.nih.gov/13079850/)\n11. [WHO EMRO seminar document EM/SEM.PH.EC.ASF.ROD.CTL/12](https://applications.emro.who.int/docs/EM_SEM_PH_EC_ASP_ROD_CTL_12_EN.pdf)\n12. [Coumachlor substance infocard, ECHA](https://chemicalsinourlife.echa.europa.eu/sv/web/guest/substance-information/-/substanceinfo/100.001.254?_disssubsinfo_WAR_disssubsinfoportlet_substanceId=100.001.254)\n13. [Table I, method originating laboratory in-house validation data, Oxford Academic](https://academic.oup.com/view-large/406408876)\n14. [Chen Y et al. (2023). Validation and interlaboratory comparison of anticoagulant rodenticide analysis in animal livers, Journal of Veterinary Diagnostic Investigation](https://journals.sagepub.com/doi/10.1177/10406387231178558)\n15. [Armentano A et al. (2012). Validation and application of multi-residue analysis of eight anticoagulant rodenticides, Journal of Veterinary Diagnostic Investigation](https://journals.sagepub.com/doi/full/10.1177/1040638711433354)\n16. [EFSA Journal (2017) scientific report on the 2015 EU coordinated pesticide monitoring programme](https://www.gastronomiaycia.com/wp-content/uploads/2017/04/Authority-2017-EFSA_Journal.pdf)\n17. [University of California report on anticoagulant rodenticide detections](https://escholarship.org/content/qt7xf8b9kp/qt7xf8b9kp_noSplash_528a84be46174693b5cdba259c834397.pdf?t=nd83yc)\n18. [pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC6996659/)\n\n---\n*Topic: Encyclopedia › Life and health › Applied biology and nonhuman health › Plant disease and plant protection › Pesticides › Rodenticides*\n\n*Initially written Oct 21, 2026*\n\n*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*\n\nLicense: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license\n", "same_as": [], "url": "https://www.edgepedia.org/coumachlor", "markdown_url": "https://www.edgepedia.org/coumachlor.md", "license": { "name": "Edgepedia Community License 1.0", "url": "https://www.edgepedia.org/edgepedia/license", "summary": "Free with credit, commercial use included. AI training is open to everyone. For other uses, organizations over USD 100M in revenue or 100M monthly users license separately.", "spdx": "LicenseRef-Edgepedia-Community-1.0" }, "credit": "\"Coumachlor\", Edgepedia (EdgeChat), https://www.edgepedia.org/coumachlor. Edgepedia Community License 1.0.", "credit_md": "\"[Coumachlor](https://www.edgepedia.org/coumachlor)\", Edgepedia (EdgeChat), [https://www.edgepedia.org/coumachlor](https://www.edgepedia.org/coumachlor). [Edgepedia Community License 1.0](https://www.edgepedia.org/edgepedia/license).", "credit_html": "\"Coumachlor\", Edgepedia (EdgeChat), https://www.edgepedia.org/coumachlor. Edgepedia Community License 1.0.", "speakable": "Coumachlor is a first-generation hydroxycoumarin anticoagulant rodenticide and warfarin analog, a vitamin K antagonist, historically used in Canada, France, Germany, and Malaya and now largely unregistered." }