Pesticides (Organophosphate & Paraquat Toxicities)

TOXICITY OF PESTICIDES

• Pesticide is a world that is consisted of 2 parts: • Pest = unwanted creature or living • Cide = killing or elimination • Pesticides include several categories such as

hebicides, insecticides, fungicides, bacteriocides, etc. • The 3 major groups to be studied in our course are:

Insecticides: organophophates. Herbicides: paraquat. Rodenticides: anticoagulants

Dr. TAHAR ABDULAZIZ MD, PhD

ORGANOPHOSPHATE TOXICITY

• Garden and household pesticides, and in agriculture.

• Formulations include liquids, sprays, and powders.

• In veterinary medicine they are found in pedicullicide lotions.

• Shampoos, aqueous and alcoholic lotions are also used as human pedicullicides and scabicides.

• Organophosphate nerve agents may be used as chemical warfare agents. An example was sarin used in the Tokyo subway attacks of 1995.

• Parathion is an organophosphate insecticide that is widely used in agriculture in Libya.


• OP bind ChE and inhibit its function excess of ACh in synapses and NMJ muscarinic and nicotinic symptoms and signs.

• Excess ACh in the synapse can lead to 3 sets of symptoms and signs: 1) At postganglionic muscarinic synapses lead to SLUDGE/BBB.

2) At nicotinic motor end plates causes persistent depolarization of skeletal muscle resulting in fasciculations, progressive weakness, and hypotonicity.

3) OP cross the blood-brain barrier, they may cause seizures, respiratory depression, and CNS depression for reasons not completely understood.

• OP bind to RBC cholinesterase & plasma cholinesterase (pseudocholinesterase) in the serum.

• The kinetics of the enzyme will reach zero within 10 hours i.e. all enzyme will be in the form of OP-AchE complex, this situation is called aging phenomenon.




Causes

Agricultural exposure is the most common cause.

The WHO classifies these poisonings as class I (extremely toxic) to class III (slightly hazardous).

The WHO advocates banning or strong restrictions on the use of class I pesticides and a reduction in the use of pesticides to a minimal number of compounds that are less hazardous than others.

Organophosphates are used as chemical warfare agents (nerve agents such as sarin, VX, or soman).



Ach & AChE




Clinical Manifestations

• Pesticides can rapidly be absorbed through the skin, lungs, GI tract, and mucous membranes.

• Symptoms usually occur within a few hours after GI ingestion and appear almost immediately after inhalational exposure.


cholinergic toxic syndrome

1- Muscarinic effects: SLUDGE/BBB mnemonic S = Salivation L = Lacrimation U = Urination

D = Defecation G = GI symptoms E = Emesis

B = Bronchorrhea B = Bronchospasm B = Bradycardia

2- Nicotinic effects at neuromuscular junctions and autonomic ganglia: weakness, fasciculations, and paralysis.

3- CNS effects may lead to seizures and CNS depression.


Plasma cholinesterase (pseudocholinesterase) &

RBC cholinesterase levels

• Laboratory evidence of OP poisoning may be obtained by measuring decreases in:

– Plasma pseudocholinesterase (PChE) and

– RBC acetylcholinesterase (RChE) activities

• Significant depression of enzyme activity may occur but still fall within the “normal” range.

– It is most helpful if the patient had a pre-exposure baseline measurement for comparison (eg, as part of a workplace health surveillance program).

•

TAHAR ABDULAZIZ MD, PhD ([email protected])

a. The RChE activity provides a more reliable measure of the toxic effect; a 25% or greater depression in activity from baseline generally indicates a true exposure effect.

b. PChE activity is a sensitive indicator of exposure but is not as specific as RChE activity

PChE may be depressed due to genetic deficiency

medical illness

chronic organophosphate exposure

PChE activity usually recovers within weeks after exposure

RChE may recover after several months

• Carbamate poisoning produces reversible AchE inhibition, and spontaneous recovery of enzyme activity may occur within several hours, making these tests less useful.


Treatment

Airway, breathing, and circulation (ABCs):

Decontamination is an important part of the initial care. In general, the importance of decontamination depends on the route of poisoning.

Patients with dermal and inhalation exposures are more likely to cause nosocomial poisoning than patients with GI exposure. Patients with GI exposure should also be decontaminated.

Patients with dermal and inhalation poisonings must be decontaminated before being brought into the ED.

Case reports have described nosocomial poisoning in staff members treating patients who have been exposed to OP; one describes OP toxicity from mouth-to-mouth resuscitation.


Atropine is a pure muscarinic antagonist that competes with ACh at the muscarinic receptor.

Atropine is most commonly given in intravenous (IV) form at the recommended dose of 2-5 mg for adults and 0.05 mg/kg for children with a minimum dose of 0.1 mg to prevent reflex bradycardia.

Atropine may be repeated every 5-10 minutes.

Severe organophosphate poisonings often require hundreds of milligrams of atropine.

Observation of 3 major signs:

dryness of mouth

flushing of face

dilatation of pupils. Dr. TAHAR ABDULAZIZ MD, PhD

Oximes {Pralidoxime (2-PAM)}:

Organophosphates bind and phosphorylate one of the active sites of AChE and inhibit the functionality of this enzyme. Oximes bind to the organophosphate, causing the compound to break its bond with AChE. Most of the effects are on the peripheral nervous system because entry into the CNS is limited.

The WHO protocol for oxime therapy is recommended for any patient with clinically significant poisoning.


Difference between OP & Carbamates


Complications: 1- Intermediate syndrome (1-4 DAYS AFTER)

sudden respiratory paresis, with weakness in cranial nerves and proximal-limb and neck flexor muscles.

2- OP-induced delayed neurotoxicity (OPIDN) (9-14 DAYS)

A sensorimotor polyneuropathy with distal motor weakness and sensory paresthesias in the lower extremities, which may progress proximally and eventually affect the upper extremities.

3- Pancreatitis

Pancreatitis has been reported as a rare complication. One case series reported that 12.76% of OP poisonings were associated with acute pancreatitis, though this has not been the experience in other series.


PARAQUAT TOXICITY

• Non-selective, water soluble herbicide (weed

killer).

• It is used since 1962.

• It is available as an aqueous concentrate and in

granular formulations

• In Libya there are 2 compounds:

– Gramaxone (yellowish liquid)

– Weedol (granulation form)


Pathophysiology

• Paraquat is very toxic when ingested. The exact

mechanisms of toxicity is not fully understood.

• The lethal dose is 1-4 grams.

• Lungs are the main target of paraquat due to

active, energy-dependent uptake by alveolar type I

and II cells.

• Skin absorption is poor. Inhalation is a possible

route of toxicity


• Ingestion is the most common route of

toxicity:

• MILD: INGESTION OF LESS THAN 20

MG/KG BODY WEIGHT.

• MODERATE TO SEVERE: INGESTION

OF 20-40 MG/KG. P

• VERY SEVERE: INGESTION OF MORE

THAN 40 MG/KG. DEATH MAY OCCUR

WITHIN 24 HOURS BUT NEVER AFTER

MORE THAN 7 DAYS.


Mechanism of toxicity • Paraquat may cause lesions in the lung by a mechanism

known as redox cycling. These compounds are reduced by

cytochrome P450 reductase forming a free radical.

• Free radical with tissue macromolecules, one molecule of

oxygen is reduced to superoxide that can then be converted

to other toxic oxygen species.

• These reactive compounds may cause peroxidation of

cellular membranes.

• The specific toxicity of paraquat to the lung results from

the uptake of this compound by lung due to high

pulmonary oxygen tension.


Formatio of superoxide radical

by PQ


• Toxicity may occur through

oxidation/reduction cycle

producing peroxides and free

radicals. • Free radicals are chemical elements that may

be positively or negatively charged or neutral

but possess a single unpaired electron


Clinical Manifestations

Phase 1: (GIT phase): may start immediately till 72 hours; intense pain in mouth, pharynx, and stomach due to the corrosive effect of paraquat. There may be bloody vomiting or diarrhea.

Phase 2: (systemic; renal or hepatic phase): severity depends on the dose of paraquat, where manifestations of renal and or hepatic failure appear.

Phase 3: (respiratory phase): in which signs of respiratory illness appear such as cough or cyanosis


Management

• There is no specific treatment; supportive therapy is

important.

• Gastric lavage with AC

• Gastric lavage with aqueous suspension of clay (Fuller Earth

or Bentonite clay).

• To avoid excessive oxygen administration as this may

aggravate lipid peroxidation reactions in the lungs.

Significant hypoxemia to be treated with supplemental

oxygen; only the lowest oxygen concentration necessary to

achieve a pO2 of about 60 mm.

• Charcoal hemoperfusion

• Hemodialysis anf forced diuresis are not effective


Pesticides (Organophosphate & Paraquat Toxicities)

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