Anticoagulant rat poison — superwarfarin poisoning
Who needs hospital, why the INR on arrival tells you nothing, and why giving vitamin K early is the commonest mistake here.
Do not give vitamin K before you have assessed for coagulopathy. It masks the onset and severity of the poisoning and destroys the value of the 48–72 hour INR — the one test that separates a patient who needs nothing from one who needs months of treatment. Grade D
Every recommendation on this page carries an evidence tier, and the graded ones carry the guideline's own grade.Guideline / position paperCohort or seriesCase reports / expert opinion
This arm rests on a genuine evidence-based consensus guideline from the American Association of Poison Control Centers, AACT and ACMT — the strongest source in the poisoning suite after the corrosive arm.
National Poisons and Drug Information Centre, Jinnah Postgraduate Medical Centre (JPMC), Karachi — 0800-77767 Reported as a round-the-clock toll-free service. Confirm the current number against your own hospital directory before relying on it in an emergency.
Decision-support only, and note the scope. The guideline states it was developed for conditions prevalent in the US and should not be extrapolated to other settings unless the assumed conditions are present. Its 1 mg threshold assumes consumer products at 0.005% — read the concentration on the product actually ingested.
✓ Clinically reviewed by Dr Syed Usama Hussain, MBBS, BSc · 05 Aug 2026.
Step 1 · Triage — does this patient need hospital?
AAPCC/AACT/ACMT consensus guideline
Tick everything that applies. The recommendations are evaluated in the guideline's own priority order.
About that 1 mg threshold Guideline / position paper
The guideline's threshold assumes US consumer products, where brodifacoum is usually formulated at 0.005%. Concentrations in commercially available rodenticides range from 0.005% to 99%, and the guideline states plainly that it was developed for conditions prevalent in the US, that available formulations and active ingredients may differ elsewhere, and that it should not be extrapolated to other settings unless the assumed conditions are present. Read the concentration on the product actually ingested before applying the threshold.
Step 2 · Why the admission INR means nothing
AAPCC/AACT/ACMT consensus guideline
The single most important thing to get right Guideline / position paper
The PT or INR is the best screening test when performed 48–72 hours after exposure.
A normal INR on arrival means nothing. The onset of anticoagulation is delayed by hours to days because clotting factors already in the circulation are still working. In a prospective series, prothrombin times taken at 48 hours were far more likely to be abnormal than those at 24 hours — 17% versus 1.9% — and a single PT at 24 hours would have missed four of eight cases.
The test that lets you stop worrying. A normal INR at 48–72 hours is what excludes a toxic ingestion. That is the test that lets you stop worrying, not the one on admission.
Serum brodifacoum concentrations have been reported as useful in documenting exposure and deciding when vitamin K therapy can be stopped; coagulopathy is unlikely below 10 ng/mL. Most laboratories do not measure it but can arrange transport to a reference laboratory.
What the poison actually does
They inhibit vitamin K 2,3-epoxide reductase and vitamin K quinone reductase, preventing activation of clotting factors II, VII, IX and X. Prothrombin time prolongs once vitamin K-dependent factor levels fall below 25–30% of normal. The onset of anticoagulation after ingestion is usually delayed for several hours to days, because of the active clotting factors already circulating at the time of ingestion.
Clinical manifestations range from asymptomatic to active bleeding — haematuria, epistaxis, menometrorrhagia, soft tissue bruising, haemarthrosis, anaemia, haemoptysis, and retroperitoneal and intracranial haemorrhage.
The child who ate the bait almost certainly needs nothing Guideline / position paper
Of more than 20,000 unintentional childhood exposures reviewed in the guideline literature, only 14 cases of prolonged PT-INR were reported (INR range 1.22–2.6) and none demonstrated bleeding. Only one patient had an INR greater than 2. A 20-year review of the US poison-centre database found no LAAR-related deaths in children under 6.
But read the limits. This applies to acute, unintentional ingestion of a ready-to-use bait. It does not apply to a deliberate ingestion, a chronic one, or a child who is already bleeding — each of those goes straight to hospital regardless of dose.
Step 3 · What not to do
AAPCC/AACT/ACMT consensus guideline
Do not give vitamin K before you have assessed for coagulopathy Grade DGuideline / position paper
The administration of vitamin K is not recommended prior to evaluation for coagulopathy.
This is the error that matters most. Prophylactic vitamin K masks the onset and severity of the poisoning and destroys the value of the 48–72 hour INR — the one test that would have told you whether this patient needed months of treatment or nothing at all. No US poison centre surveyed for the guideline recommended prophylactic vitamin K.
Do not induce emesis, and do not perform gastric lavage Grade DGuideline / position paper
Gastrointestinal decontamination with ipecac syrup or gastric lavage is not recommended.
In a reported case, ipecac caused severe vomiting followed by subarachnoid haemorrhage and death in an adult with brodifacoum poisoning. Straining to vomit in an anticoagulated patient is its own mechanism of injury.
Do not delay transport to give activated charcoal Grade DGuideline / position paper
Transportation to an emergency department should not be delayed for administration of activated charcoal.
No human study has assessed charcoal binding for these compounds. In pediatric unintentional ingestions there was no significant difference in outcome between patients who received any form of gastrointestinal decontamination and those who did not, and multiple-dose charcoal did not shorten the duration of vitamin K therapy in two reported cases.
Do not overlook skin exposure Grade DGuideline / position paper
Patients with dermal exposures should be decontaminated by washing the skin with mild soap and water.
Dermal absorption of a liquid preparation has been reported — one man developed haematuria and a markedly prolonged PT a week after spilling a concentrated liquid formulation into his boot and continuing to wear it.
Step 4 · Vitamin K1 — once coagulopathy is documented
Consensus guideline + superwarfarin literature
Vitamin K1 (phytomenadione) is started once coagulopathy is documented — not before. It treats the coagulopathy; it does not remove the poison, and the poison outlasts it.
Oral is the preferred route, and this is not a minor preference Cohort or series
Intravenous phytomenadione carries a black box warning for anaphylactoid reactions, which have been associated with fatalities. The reported incidence is around 3 per 10,000 doses, and the reaction is attributed to the polyethoxylated castor oil vehicle rather than to vitamin K itself. Reserve the intravenous route for serious bleeding, and give it slowly and diluted.
Dose is titrated against the INR, not fixed Cohort or series
A commonly cited oral starting point in documented coagulopathy is 100 mg per day in four divided doses. Reported total daily doses range from about 25 mg to 400 mg.
Divided dosing matters — a less frequent regimen may not be effective, because the antagonist outlasts each dose of vitamin K.
Titrate to the PT/INR and expect to continue for weeks to months. In the guideline literature, treatment was often required for weeks to months, and in one pregnancy case daily oral vitamin K1 50 mg was continued until delivery, with a healthy infant at term.
Caravati et al. 2007 for duration and requirement; dosing ranges and the anaphylaxis data from the wider superwarfarin literature
Step 5 · Active bleeding
Reported practice — no controlled data
Active bleeding is a different problem from a raised INR Case reports / expert opinion
Vitamin K1 takes hours to work because clotting factors must be resynthesised. It is the treatment, but it is not the immediate one.
For active or life-threatening haemorrhage, replace factors — fresh frozen plasma or prothrombin complex concentrate — alongside vitamin K1, not instead of it.
Recombinant activated factor VII has been used in a small number of reported patients. There are no prospective or controlled data supporting the efficacy of any of these measures.
Therapeutic plasma exchange has been used as a second-line measure in brodifacoum poisoning after an anaphylactoid reaction to vitamin K.
Transfuse and treat the bleeding site as you would any coagulopathic haemorrhage — compression, endoscopy, surgery, iron replacement.
Caravati et al. 2007 notes these treatments were reported without prospective or controlled data supporting efficacy
Step 6 · The long tail
AAPCC/AACT/ACMT consensus guideline
This one is measured in months Guideline / position paper
Serum brodifacoum half-life ranged from 16 to 34 days after overdose. The duration of action of brodifacoum ranged from 46 days to 9 months after intentional overdose. Treatment with vitamin K was often required for weeks to months.
The duration of action of brodifacoum ranged from 46 days to 9 months after intentional overdose. Do not plan a one-week course.
Expect rebound coagulopathy when vitamin K is reduced or stopped — recheck the INR after each step down, not just at the end.
Serum LAAR concentrations, where obtainable, help decide when treatment can stop; coagulopathy is unlikely below 10 ng/mL for brodifacoum.
Supplemental vitamin K can persist for up to 2 weeks and will interfere with subsequent therapeutic anticoagulation — flag this if the patient needs warfarin later.
Compliance is part of the treatment. A patient who stops taking vitamin K at home after a deliberate ingestion is at risk for months, so follow-up and the psychiatric assessment are not optional extras.
Almost all of these ingestions are deliberate self-harm.
Psychiatric evaluation is mandatory in all patients prior to hospital discharge (Grade 2C). Long-term control of the psychiatric disease is important to avoid recurrence.
A patient who is medically fit for discharge is not therefore fit for discharge. The guideline makes the psychiatric assessment a requirement, not a courtesy — and the ingestion pattern (deliberate versus accidental) is itself among the strongest predictors of how bad the injury will be.
WSES Esophageal Emergencies guidelines, 2019
Common questions
Should I give vitamin K straight away?
No. The consensus guideline states that the administration of vitamin K is not recommended prior to evaluation for coagulopathy (Grade D). Prophylactic vitamin K masks the onset and severity of the poisoning and destroys the value of the 48–72 hour INR — the one test that distinguishes a patient who needs nothing from one who needs months of treatment.
The INR is normal on arrival. Can I discharge the patient?
Not on that basis. Anticoagulation is delayed by hours to days because clotting factors already in the circulation are still working. The PT or INR is the best screening test when performed 48–72 hours after exposure. In one prospective series, PTs at 48 hours were abnormal in 17% versus 1.9% at 24 hours, and a single test at 24 hours would have missed four of eight cases.
A child ate some rat poison pellets. What now?
If it was an acute unintentional ingestion of less than 1 mg of active ingredient, the guideline says the child can be safely observed at home without laboratory monitoring — and that this covers practically all unintentional ingestions in children under 6 (Grade C). Of more than 20,000 unintentional childhood exposures reviewed, only 14 had a prolonged INR and none bled. That does not apply if the ingestion was deliberate, chronic, or the child is already bleeding.
Who needs to go to an emergency department immediately?
Three groups, regardless of the dose reported: suspected self-harm, abuse, misuse or malicious administration (Grade D); anyone with symptoms such as bleeding or bruising (Grade C); and anyone with chronic ingestion (Grade B).
Should I do gastric lavage or give activated charcoal?
Gastrointestinal decontamination with ipecac syrup or gastric lavage is not recommended (Grade D) — in one reported case ipecac caused severe vomiting followed by fatal subarachnoid haemorrhage. Transport to hospital should not be delayed to give activated charcoal (Grade D).
Oral or intravenous vitamin K1?
Oral is preferred. Intravenous phytomenadione carries a black box warning for anaphylactoid reactions that have been associated with fatalities, at roughly 3 per 10,000 doses, attributed to the castor oil vehicle rather than the vitamin. Reserve the intravenous route for serious bleeding.
How long does treatment last?
Months, not days. The duration of action of brodifacoum ranged from 46 days to 9 months after intentional overdose, and treatment with vitamin K was often required for weeks to months. Expect rebound coagulopathy when the dose is reduced, and recheck the INR after each step down.
Does the 1 mg threshold apply to Pakistani products?
Check before you use it. The guideline assumes US consumer products at 0.005% brodifacoum, while available concentrations range from 0.005% to 99%. The guideline states explicitly that it should not be extrapolated to other settings unless the assumed conditions are present.
Clinically reviewed by Dr Syed Usama Hussain, MBBS, BSc
MBBS, BSc — active medical practitioner in Pakistan. Graduated from Federal Medical & Dental College, Islamabad (2021) and completed a one-year clinical internship at the Pakistan Institute of Medical Sciences (PIMS), Islamabad (2022).
Sources
Caravati EM, Erdman AR, Scharman EJ, et al. Long-acting anticoagulant rodenticide poisoning: an evidence-based consensus guideline for out-of-hospital management. Clinical Toxicology 2007;45(1):1-22. Expert consensus panel appointed by the American Association of Poison Control Centers, the American Academy of Clinical Toxicology and the American College of Medical Toxicology. — the source of every graded recommendation quoted here.
SCOPE CAVEAT, in the guideline's own words: it "has been developed for the conditions prevalent in the US ... available formulations and active ingredients may differ for some LAAR products ... This guideline should not be extrapolated to other settings unless it has been determined that the conditions assumed in this guideline are present." The 1 mg threshold assumes consumer products at 0.005%.
Superwarfarin poisoning reviews for vitamin K1 dosing ranges, the intravenous anaphylaxis data, and the maintenance-phase experience.
Case report of therapeutic plasma exchange as second-line treatment for brodifacoum poisoning following an anaphylactoid reaction to vitamin K.
Background reading — why the admission INR is meaningless, who actually needs hospital, and why the child who ate the pellets almost certainly needs nothing: the vitamin K mistake.