DESCRIPTION

Carbamate insecticides are relatively low toxicity chemicals used in many household, agricultural, and veterinary pest control products.

FORMS AND USES

• Carbamate insecticides are classified by their relative toxicity.
• Low-toxicity products include BPMC (Fenocarb), carbaryl (Sevin), isopocarb (Etrofolan and MIPC), MPMC (Meobal), MTMC (Meacrate and Tsumacide), and XMC (Cosban), and others.
• Moderate-toxicity products include bufencarb (Bux), carbosulfan, pirimicarb (Pirimor), promecarb and thiodicarb.
• High-toxicity products include aldicarb (Temik), aminocarb (Matacil), bendiocarb (Ficam), carbofuran (Furadan), dimetan (Dimetan), dimetilan (Snip), dioxacarb (Eleocron and Famid), formetanate (Carzol), methiocarb (Mesurol), methomyl (Lannate and Nudrin), oxamyl (Vydate), and propoxur (Baygon).

TOXIC DOSE

The toxic dosage of carbamate insecticides varies due to the wide range of products available.

PATHOPHYSIOLOGY

• Like organophosphate insecticides, carbamates inhibit acetylcholinesterase, resulting in the accumulation of acetylcholine and excessive stimulation of the acetylcholine receptor.
• Unlike organophosphates, however, the inhibition is reversible.
• Toxicity may manifest as nicotinic (muscle weakness, fasciculation, hypertension, and tachycardia) or muscarinic (diaphoresis, vomiting, diarrhea, etc.) effects.

EPIDEMIOLOGY

• Poisoning is common.
• Toxic effects are typically mild to moderate.
• Death is rare and usually occurs following a massive exposure or due to delayed treatment.

CAUSES

• Toxic ingestion is usually accidental.
• Dermal or inhalation exposure is usually occupational.
• Child neglect or abuse should be considered if the patient is less than 1 year of age, suicide attempt if the patient is over 6 years of age.

RISK FACTORS

• Agricultural workers, farmers, and gardeners who use pesticides are at increased risk of carbamate poisoning.
• Patients with congenitally low levels of acetylcholinesterase are at increased risk of toxicity from a given exposure.
• Patients with recent subtoxic exposure are at increased risk during reexposure.

DRUG AND DISEASE INTERACTIONS

• Carbamates prolong the activity of some paralytic agents.
• Gentamicin and other antibiotics may prolong carbamate toxicity.

PREGNANCY AND LACTATION

Carbamates cross the placenta; fetal death after ingestion has occurred.

WORKPLACE STANDARDS

• Carbaryl
  • OSHA. PEL TWA is 5 mg/m³.
  • NIOSH. REL TWA is 5 mg/m³.
• Aldicarb is not listed.
• Carbofuran. NIOSH. REL TWA is 0.1 mg/m³.

Section Outline:

• DESCRIPTION
• FORMS AND USES
• TOXIC DOSE
• PATHOPHYSIOLOGY
• EPIDEMIOLOGY
• CAUSES
• RISK FACTORS
• DRUG AND DISEASE INTERACTIONS
• PREGNANCY AND LACTATION
• WORKPLACE STANDARDS

DIFFERENTIAL DIAGNOSIS

• Other toxicologic causes of acute onset of acetylcholine effects include organophosphates, nicotine, carbachol, methacholine, arecoline, bethanechol, pilocarpine, and certain mushrooms, among others.
• Nontoxicologic causes include myasthenia gravis and Eaton-Lambert syndrome, among others.

SIGNS AND SYMPTOMS

• Muscarinic effects are manifested by the DUMBELS syndrome (Diaphoresis and diarrhea; Urination; Miosis; Bradycardia, bronchospasm, and bronchorrhea; Emesis; excess Lacrimation; and Salivation and seizures) and usually occur soon after exposure.

Vital Signs

Bradycardia, hypotension, and hypothermia may occur.

HEENT

Miosis, blurred vision, salivation, and lacrimation are common.

Dermatologic

Profuse diaphoresis is common.

Cardiovascular

• Hypotension and bradycardia are common with muscarinic agents.
• Cardiac depression and cardiovascular collapse may occur.
• Atrial fibrillation, atrioventricular blocks, and asystole may occur.

Pulmonary

• Bronchospasm and bronchorrhea are common.
• Pulmonary edema is common in severe cases.

Gastrointestinal

Nausea, vomiting, abdominal pain, and diarrhea are common; incontinence may occur.

Renal

Urinary incontinence is common, especially in severe cases.

Musculoskeletal

Fasciculation, weakness, paralysis, and respiratory failure may occur.

Neurologic

Confusion and seizures may occur.

PROCEDURES AND LABORATORY TESTS

Essential Tests

• Red blood cell cholinesterase level correlates roughly with effects; first sample should be drawn before treatment (plasma cholinesterase can be used if red blood cell cholinesterase is unavailable).
  • Latent
    • No clinical manifestations are present.
    • Cholinesterase levels are 50% to 90% of baseline for patient.
  • Mild
    • Patient is ambulatory and may experience nausea, vomiting, fatigue, headache, dizziness, sweating and salivation, tightness in the chest, and abdominal cramps or diarrhea.
    • Cholinesterase activity is 20% to 50% of baseline.
  • Moderate
    • Patient cannot walk and experiences generalized weakness, difficulty in speaking, fasciculation, and miosis.
    • Cholinesterase activity is 10% to 20% of baseline.
  • Severe
    • Patient is unconscious, with miosis, fasciculation, flaccid paralysis, increased secretions, moist rales, respiratory difficulty, and cyanosis.
    • Cholinesterase activity is less than 10% of baseline.
• Serum electrolytes, glucose, BUN, calcium, magnesium, phosphate, and creatinine should be assayed in symptomatic patients to detect other causes of dysrhythmia, weakness, or kidney injury.
• ECG and continuous cardiac monitoring should be performed to assess potential causes of hypotension and bradycardia.

Recommended Tests

• Serum acetaminophen and aspirin levels should be measured in an overdose setting to detect occult ingestion.
• Arterial blood gases should be measured if acidosis or hypoxia develop.
• Comprehensive urine drug screen should be performed if the source of intoxication is unknown (drugs abused may contain contaminants).
• Heat CT, lumbar puncture, bacterial cultures, and other tests as indicated should be performed in patients with altered mental status of unknown etiology.
• Negative inspiratory force should be followed to assess ventilatory capacity.
• Chest radiographs will assist evaluation of pulmonary edema.

Section Outline:

• DIFFERENTIAL DIAGNOSIS
• SIGNS AND SYMPTOMS
  • Vital Signs
  • HEENT
  • Dermatologic
  • Cardiovascular
  • Pulmonary
  • Gastrointestinal
  • Renal
  • Musculoskeletal
  • Neurologic
• PROCEDURES AND LABORATORY TESTS
  • Essential Tests
  • Recommended Tests

• Treatment should focus on decontamination, airway management, and atropine administration
• Dose and time of exposure should be determined for all substances involved.

DIRECTING PATIENT COURSE

The health-care professional should call the poison control center when:

• Breathing difficulty, hypotension, or other severe effects are present.
• Toxic effects are not consistent with carbamate poisoning.
• Coingestant, drug interaction, or underlying disease presents an unusual problem.

The patient should be referred to a health-care facility when:

• Attempted suicide or homicide is possible.
• Patient or caregiver seems unreliable.
• Any toxic effects develop.
• Coingestant, drug interaction, or underlying disease presents an unusual problem.

Admission Considerations

Inpatient management is warranted if patient develops any toxic effects.

DECONTAMINATION

Out of Hospital

• Emesis should not be induced.
• Providers must wear protection to prevent contamination.
• All clothing should be removed from the patient and skin should be washed with soap and water.

In Hospital

• Health-care professionals should wear protective clothing.
• All clothing should be removed from the patient, and skin should be washed with soap and water.
• Gastric lavage should be performed in pediatric (tube size 24-32 French) or adult (tube size 36-42 French) patients for large ingestion presenting within 1 hour of ingestion or if serious effects are present.
• One dose of activated charcoal (1-2 g/kg) should be administered if a substantial ingestion has occurred within the previous few hours.

ANTIDOTES

Atropine and pralidoxime are antidotes for carbamate poisoning.

Atropine

• Indications. Control of bronchorrhea and other secretions
• Contraindication. Preexisting atropinization (dry airway, mydriatic pupils etc.)
• Method of administration
  • Adult initial dose is 2 to 4 mg intravenously; dose may be repeated every 5 to 10 minutes as needed until lungs are clear to auscultation.
  • Pediatric initial dose is 0.05 mg/kg intravenously; dose may be repeated every 5 to 10 minutes as needed until pulmonary secretions are controlled.
  • In severe cases, rapid escalation of the dose may be needed.
• Adverse effects. Anticholinergic symptoms possible with excessive atropine.

Pralidoxime (2-PAM)

• Indications. Patients who require large doses of atropine or have serious signs of cholinergic toxicity.
• Contraindication. Ingestion of carbaryl is relative contraindication.
• Method of administration
  • Adult dose is 1 to 2 g intravenously over 15 to 30 minutes or as a continuous intravenous infusion at 500 mg/h (preferred).
  • Pediatric dose is 20 to 40 mg/kg intravenously over 15 to 30 minutes.

ADJUNCTIVE TREATMENT

Hypotension

• Atropine should be used if hypotension is due to bradycardia.
• Patient should receive 10 to 20 ml/kg 0.9% saline and be placed in the Trendelenburg position.
• Further fluid therapy should be guided by central pressure monitoring to avoid volume overload.
• A vasopressor may be added if needed. Dopamine is preferred, and norepinephrine is added for refractory hypotension.

Seizure

• Patent airway must be ensured.
• Benzodiazepine should be administered for initial control. If seizures persist or recur, another anticonvulsant such as phenobarbital may be added.

Section Outline:

• DIRECTING PATIENT COURSE
  • Admission Considerations
• DECONTAMINATION
  • Out of Hospital
  • In Hospital
• ANTIDOTES
  • Atropine
  • Pralidoxime (2-PAM)
• ADJUNCTIVE TREATMENT
  • Hypotension
  • Seizure

PATIENT MONITORING

• Continuous respiratory and cardiac monitoring should be performed in symptomatic patients.
• In the case of occupational exposure, patients should not be allowed to work with organophosphate or carbamate pesticides until red blood cell cholinesterase levels have returned to 75% of known baseline.

EXPECTED COURSE AND PROGNOSIS

• Toxicity develops rapidly, peaks within hours, but may persist for days if patient does not receive antidotal treatment.
• Patients who receive early treatment usually recover without sequelae.

DISCHARGE CRITERIA/INSTRUCTIONS

• From the emergency department. Asymptomatic patients may be dishcarged after adequate decontamination, a 6-hour observation period, and psychiatric evaluation, if needed.
• From the hospital. Patients who have not required atropine for 24 hours may be discharged.

PATIENT EDUCATION

Patients should be warned not to return to work until cholinesterase levels of at least 75% of baseline have been documented.

Section Outline:

• PATIENT MONITORING
• EXPECTED COURSE AND PROGNOSIS
• DISCHARGE CRITERIA/INSTRUCTIONS
• PATIENT EDUCATION

DIAGNOSIS

Failure to adequately protect health-care providers may result in secondary exposures.

TREATMENT

Atropine should be administered until pulmonary secretions are improved; large doses may be required.

FOLLOW-UP

Patients should have demonstrated baseline or plateau of cholinesterase activity before handling pesticides again.

Section Outline:

• DIAGNOSIS
• TREATMENT
• FOLLOW-UP

Toxic effect of other substances, chiefly nonmedicinal as to source: organophosphate and carbamate.

See Also: SECTION II, Cholinergic Syndrome, Hypotension, and Seizure chapters; SECTION III, Atropine and Pralidoxime chapters; and SECTION IV, Organophosphate Insecticides chapter.

RECOMMENDED READING

Rumack BH, Sayre NK, Gelman CR, eds. POISINDEX system. Englewood, CO: MICROMEDEX, Inc. (edition expires November 30, 1997).

Author: Kennon Heard

Reviewer: Luke Yip