8.2 Rodenticides, Herbicides, Repellents, and Other Pesticides
Key Takeaways
- A small unintentional taste of a long-acting anticoagulant rodenticide by a child does not require prophylactic vitamin K or routine testing, whereas an intentional or large ingestion requires an INR at 48 to 72 hours and may need months of high-dose oral vitamin K1.
- Non-anticoagulant rodenticides are more dangerous than the anticoagulants: bromethalin uncouples oxidative phosphorylation and causes cerebral edema, cholecalciferol causes hypercalcemia, and metal phosphides generate phosphine gas that endangers rescuers.
- Strychnine causes awake convulsions with intact consciousness through glycine receptor antagonism, and management is aggressive benzodiazepine sedation, paralysis if needed, and a dark quiet environment.
- Chlorophenoxy herbicides respond to urinary alkalinization, glyphosate toxicity is driven largely by its surfactant, and the bipyridyls (paraquat, diquat) remain the most lethal herbicides with oxygen restriction as a key rule.
- Boric acid produces vomiting, diarrhea, and a blue-green emesis with a characteristic boiled-lobster erythroderma, while DEET is well tolerated in ordinary use and lindane is a seizure risk that must never be reapplied.
Anticoagulant Rodenticides
Long-acting anticoagulant rodenticides ("superwarfarins") include brodifacoum, bromadiolone, difethialone, and difenacoum. Like warfarin, they inhibit vitamin K epoxide reductase, depleting the reduced vitamin K needed to activate factors II, VII, IX, and X, and proteins C and S. Unlike warfarin, they are highly lipophilic and have half-lives measured in weeks to months.
Triage: The Two Very Different Cases
| Scenario | Approach |
|---|---|
| Unintentional small taste by a child (the overwhelming majority of calls) | Bait pellets contain a very low concentration (commonly 0.005%), so a taste or a few pellets is a non-toxic exposure. No prophylactic vitamin K, no routine INR, no charcoal. Provide reassurance and follow-up, with instructions to report bleeding or bruising |
| Intentional ingestion, repeated ingestion, large volume of concentrate, or a patient already anticoagulated | Activated charcoal if early; obtain an INR at 48 to 72 hours (an initial INR is usually normal and falsely reassuring because factor VII must first decay) |
Treatment When Coagulopathy Develops
- Active bleeding: four-factor prothrombin complex concentrate or fresh frozen plasma plus intravenous vitamin K1 (phytonadione). Vitamin K corrects the defect over hours, not minutes, so factor replacement is what stops bleeding now.
- Elevated INR without bleeding: oral vitamin K1 in high doses (often 25 to 50 mg three or four times daily in adults), titrated to the INR.
- Duration: weeks to months, with periodic INR monitoring and a tapering dose. Stopping too early causes rebound coagulopathy.
- Do not use intramuscular vitamin K in a coagulopathic patient, and avoid unnecessary invasive procedures.
Adulteration alert: outbreaks of brodifacoum-contaminated synthetic cannabinoid products have produced clusters of severe coagulopathy with hematuria and intracranial hemorrhage. Consider it in any bleeding patient who uses those products.
Non-Anticoagulant Rodenticides
| Agent | Mechanism | Presentation | Management |
|---|---|---|---|
| Bromethalin | Uncouples oxidative phosphorylation in the central nervous system, producing cerebral edema | Onset hours to days: vomiting, tremor, ataxia, seizures, coma; no antidote | Charcoal (including multiple doses), seizure control, management of intracranial pressure |
| Cholecalciferol (vitamin D3) | Massive vitamin D load | Delayed hypercalcemia over 1 to 3 days: vomiting, weakness, polyuria, kidney injury | Saline hydration, loop diuretic, then bisphosphonate or calcitonin for severe hypercalcemia; serial calcium for days |
| Zinc or aluminum phosphide | Liberates phosphine gas on contact with moisture or acid | Vomiting, garlic odor, profound shock, metabolic acidosis, multi-organ failure; very high mortality | Supportive care only; decontaminate with the rescuer protected, because phosphine off-gassing from vomitus has poisoned emergency staff |
| Strychnine | Competitive antagonist at spinal glycine receptors | Painful generalized muscle contractions with preserved consciousness, risus sardonicus, opisthotonos triggered by noise or touch; hyperthermia and rhabdomyolysis | Benzodiazepines in large doses, dark quiet room, paralysis and ventilation if needed; treat hyperthermia and rhabdomyolysis |
| Sodium monofluoroacetate (compound 1080) | Blocks the citric acid cycle by forming fluorocitrate | Vomiting, seizures, dysrhythmias, hypocalcemia; extremely lethal | Supportive; restricted-use product |
| Thallium (historical) | Potassium mimic | Painful neuropathy, then alopecia, Mees lines | Prussian blue |
Borates and Boric Acid
Boric acid, borax, and sodium perborate appear in ant and roach baits, contact lens solutions, and some cleaning powders.
- Single small ingestions of bait products are usually benign.
- Large ingestions cause vomiting and diarrhea that may be blue-green, abdominal pain, and a diffuse erythroderma that desquamates, classically described as a "boiled lobster" appearance.
- Severe cases produce seizures, kidney injury, and shock. Management is supportive with fluids; charcoal does not bind borates well, and hemodialysis is used in severe poisoning with kidney failure.
Chlorinated Hydrocarbon Insecticides
Lindane, dieldrin, aldrin, chlordane, and DDT act on neuronal sodium channels and GABA-gated chloride channels, producing central nervous system excitation.
- Lindane is still used medically for scabies and lice. Toxicity follows ingestion, excessive or repeated topical application, or use on broken skin, and appears as agitation, tremor, and seizures.
- Rule: never reapply a lindane product, never use it after a hot bath, and avoid it in infants, pregnancy, and patients with seizure disorders. Permethrin is the preferred alternative.
- Treatment is decontamination (skin washing), benzodiazepines for seizures, and avoidance of oil-based cathartics, which increase absorption of lipophilic pesticides.
Insect Repellents
| Repellent | Toxicity |
|---|---|
| DEET (N,N-diethyl-m-toluamide) | Very widely used with an excellent safety record at label concentrations. Reported seizures, mostly with massive ingestion or heavy repeated application to young children; dermal irritation is common. Concentrations of 10% to 30% are recommended for children |
| Picaridin | Low toxicity; irritation only |
| Oil of lemon eucalyptus (p-menthane-3,8-diol) | Ocular irritant; not recommended under 3 years of age |
| Permethrin-treated clothing | Minimal human absorption |
| Citronella | Minimal systemic toxicity; the essential oil itself is a concern if ingested in volume |
Herbicides
| Class | Examples | Toxicity and Management |
|---|---|---|
| Bipyridyls | Paraquat, diquat | The most lethal herbicides. Paraquat concentrates in lung tissue and redox cycles, producing progressive pulmonary fibrosis; withhold supplemental oxygen unless hypoxia is life-threatening. Diquat spares the lung but causes severe gastrointestinal and kidney injury and central nervous system hemorrhage |
| Chlorophenoxy compounds | 2,4-D, MCPA, mecoprop | Vomiting, muscle pain and rhabdomyolysis, hypotension, coma, metabolic acidosis, and myotonia. Urinary alkalinization enhances elimination of these weak acids |
| Glyphosate formulations | Roundup and generics | Toxicity is driven mainly by the surfactant: corrosive mucosal injury, vomiting, hypotension, and metabolic acidosis in large intentional ingestions. Management is supportive with attention to airway and volume |
| Glufosinate | Ammonium glufosinate | Delayed (up to 12 to 24 hours) seizures, coma, apnea, and amnesia after an initially mild gastrointestinal phase; prolonged observation required |
| Triazines | Atrazine, simazine | Low acute toxicity; irritation |
| Sodium chlorate | Older defoliant | Methemoglobinemia, hemolysis, and kidney failure; methylene blue is relatively ineffective, exchange transfusion is used |
Poison Center Case: The Bait Station Call
A mother calls after finding her 18-month-old holding a chewed green pellet from a rodent bait station under the kitchen sink. The label lists bromadiolone 0.005%. The child is asymptomatic and the amount appears to be a fraction of one pellet.
Specialist reasoning. At 0.005%, a 2 g pellet contains only 0.1 mg of bromadiolone, far below any amount capable of causing coagulopathy in a 12 kg child. The CSPI provides reassurance, advises no vitamin K and no coagulation testing, and explains what bleeding signs would warrant a call back (easy bruising, nosebleeds, bleeding gums, blood in urine or stool) over the next week. The caller is also asked to confirm the product name and active ingredient from the label, because the same bait stations are sold with bromethalin, which is far more dangerous and would change the disposition to emergency evaluation. A follow-up call is scheduled, and the family receives storage counseling.
A 2-year-old chewed a corner of a rodent bait pellet containing 0.005% brodifacoum. He is asymptomatic. What is the appropriate management?
A 44-year-old ingested a rodenticide and now has vomiting, a garlic-like odor on the breath, profound hypotension, and severe metabolic acidosis. Emergency department staff begin to feel lightheaded and nauseated while suctioning gastric contents. Which agent is responsible and what is the critical safety step?
A 51-year-old farm worker ingested a chlorophenoxy herbicide concentrate and has vomiting, severe muscle pain, an elevated creatine kinase, and metabolic acidosis. Which intervention specifically enhances elimination of this class?