OVERVIEW

Ever used an insecticide on a bug or household pest? Some of us probably enjoyed watching these little critters struggling for their lives as they suffocated to death. Well not to spoil the fun but what could happen to us if we were intoxicated with an insecticide? In actual fact, we would be in a more critical condition than the insects.

Insecticides, herbicides, and weedicides contain chemical compounds such as organophosphates or carbamates which equally affects both insects and humans. Since most insecticide and herbicide products on the market contain organophosphates, we would set our focus in this area.

What then is organophosphate poisoning?

DEFINITION

Organophosphate poisoning or toxicity refers to a clinical condition caused by the ingestion, inhalation or topical absorption (absorption through the skin) of organophosphate compounds. It is diagnosed based on the clinical presentation of symptoms including coughing, eye tearing, cardiac problems, and breathing difficulties.

An occupational or social history involving exposure to insecticides or herbicides also aids in the diagnosis.
We know of insecticides containing organophosphate but what other chemical agents contain this compound?

ETIOLOGY

Organophosphate compounds are a diverse group of chemicals used not in the domestic setting but also in industrial settings. Below are some examples of organophosphate products:

• Insecticides – Malathion, parathion, diazinon, fenthion, dichlorvos, chlorpyrifos, ethion
• Ophthalmic agents – Echothiophate, isoflurophate
• Antihelmintics – Trichlorfon
• Herbicides – Tribufos, merphos
• Industrial chemicals (plasticizer) – Tricresyl phosphate
• Nerve gas – Soman, sarin, tabun

EPIDEMIOLOGY

Worldwide, pesticide poisoning is among the most common modes of poisoning fatalities. Countries such as India, have a prevalence of pesticide poisoning due to easy accessibility of organophosphates. Therefore, it serves as a source of both intentional and unintentional poisonings.

Children are affected by organophosphates normally involving delayed or persistent effects. Mortality studies worldwide report mortality rates from 3-25%. Compounds most frequently involved in mortality are malathion, dichlorvos, trichlorfon and fenitrothion.

Most mortality rates are dependent on the type of compound used, amount ingested, patient’s general health, delay in discovery and transport, insufficient respiratory management and delay in intubation.

PATHOPHYSIOLOGY

Organophosphates are absorbed through the gastrointestinal tract, lungs and skin. They inhibit an enzyme called acetylcholinesterase (AChE) present in the plasma, nerve synapse (CNS and PNS), and red blood cells. The action of AChE is to degenerate acetylcholine after it has exerted its effects. Acetylcholine is a neurotransmitter in the parasympathetic nervous system which acts on nicotinic and muscarinic receptors. Inhibition of AChE leads to the accumulation of acetylcholine with a resultant effect of parasympathetic overdrive and eventually dysfunction.

The parasympathetic nervous is responsible for our involuntary actions at rest. The medical mnemonic DUMBELSS (Diarrhea, Urination, Miosis/Muscle weakness, Bronchorrhea, Bradycardia, Emesis, Lacrimation, Salivation, and Sweating) is one of the simplest methods to help you recollect the symptoms of parasympathetic activation.

Unlike carbamates which are cleared spontaneously within 48 hours after exposure, organophosphates irreversibly bind to cholinesterase.

SIGNS AND SYMPTOMS

In organophosphate poisoning, the symptoms are categorized into three broad groups. These are:

1. Muscarinic effects:

• Salivation
• Lacrimation (Eye tearing)
• Urinary incontinence
• Diarrhea
• GI upset
• Emesis (Vomiting)
• Diaphoresis (Increased sweating)
• Miosis (Constricted pupils)
• Bradycardia (Decreased pulse rate)
• Bronchospasm (asthma like-symptoms)
• Bronchorrhea (Mucus secretions in the bronchus)
• Abdominal pain
• Rhinorrhea
• Severe respiratory distress

2. Nicotinic effects:

• Muscle spasms
• Muscle cramps
• Weakness
• Diaphragmatic failure
Hypertension
• Tachycardia (Increased pulse rate)
• Mydriasis (Dilated pupils)
• Pallor

3. Central Nervous System effects:

• Anxiety
• Emotional lability
• Confusion
• Restlessness
• Ataxia
• Tremors
• Seizures
• Coma
• Apnea

There could also be other neuropsychiatric effects such as impaired memory, lethargy, psychosis, and irritability.

DIAGNOSIS

Symptoms and description of events surrounding the poisoning serve as the basis for diagnosis of organophosphate poisoning. The following can also assist your general practitioner in diagnosing organophosphate poisoning:

• History of exposure to insecticides and characteristic symptoms
• Blood tests

Diagnosis is also confirmed when a drug called atropine, is given intravenously to relieve the symptoms of the patient. Blood tests also confirm the levels of organophosphate or carbamate in the blood.

TREATMENT

Organophosphate poisoning, just as any other medical emergency requires a rapid and efficient response in saving the life of the patient and prevent further deterioration.

First of all, decontamination is key to preventing further intoxication. Clothing is removed and patients are gently cleansed with soap and water. All clothing should be discarded since it poses a hazardous risk.

Health care workers should wear protective equipment when decontaminating patients. Active charcoal is given for ingestion within 1 hour of presentation.

Supportive therapy is key to ensuring the patient’s survival. Patients are monitored for respiratory failure due to weakness of respiratory muscles. Patients are intubated if there are signs supportive of respiratory depression or failure.

The following medications are given in counteracting the effects of organophosphates:
• Atropine for respiratory manifestations
• Pralidoxime for neuromuscular manifestations