4. Common OP pesticides with their brands
available in Nepal
OP pesticide Brands available
Methyl parathion Metacid, Parahit, Paradol
Dichlorovos Nuvan, DDVP, Nudan, Suchlor
Dimethoate Rogor, Roger, Rogohit
Chlorpyrifos Durmet, Dhanuban, Radar
Fenthion Dalf, Baytex
Profenofos Current
Quinalphos Krush
Monocrotophos Phoskill
8. AGEING
Irreversible inhibition of acetylcholinesterase due to phosphorylation
of the active site of the enzyme(serine hydroxl group) and with time
the enzyme-OP complex loses one alkyl group making it no longer
responsive to reactivating agents.
Ageing time
Dimethyl – 3.7 hours
Diethyl – 31 hours
Nerve agents – within minutes
Carbamate-no ageing
Spontaneous reactivation half life
Dimethyl - 0.7hours
Diethyl - 31 hours
Carbamate-30-40 minutes
11. Muscarinic effects(parasympathetic)
D iarrhoea, Abdominal cramps
U rinary incontinence
M iosis
B radycardia, Hypotension, Ventricular tachycardia
E mesis
L acrimation
S alivation
Pulmonary oedema, bhronchospasm, bronchorrhea
15. Intermediate syndrome
Usually occurs after 24 to 96 hours of ingestion.
last up to 5-14 days
Approximately 10-40% of patients develop this
illness.
Characterized by prominent weakness ocular
muscles to neck flexors, muscles of respiration
and proximal limb muscles.
Require ventilatory care.
16. DELAYED POLYNEUROPATHY (OPIDN)
Uncommon consequence of severe intoxication or intermittent and
chronic contact
Due to inhibition of neuropathy target esterase (NTE) enzyme in
nervous tissues
Chlorpyrifos(Durmet, Dhanuban, Radar) causes comparatively more
degree of inhibition of NTE
Clinical manifestations are of distal symmetric sensory-motor
polyneuropathy (muscle cramp, distal weakness, parasthesia, ataxia,
diminished or absent reflexes, flaccid paralysis)
usually begin 2-5 weeks after exposure and may last for years.
No specific therapy but regular physiotherapy may limit the deformity.
18. DIAGNOSIS
History of exposure to OP compounds.
Characteristics manifestations like Pinpoint pupil, Muscle
fasciculation, characteristic (garlic) smell of stomach aspirate
In case of doubt atropine challenge test can be done
1-2mg iv atropine is given, if it doesn’t produce dry skin,
dry mucosa, tachycardia and mydriasis in 15-20 minutes patient
has to be treated in the line of OP.
19. LAB TEST
Limited value as treatment is usually required before test results are
available
Level of plasma (pseudo) cholinesterase drops to less than 50%( Normal
value 3000-6000IU/L)
Clinical severity has been graded on the basis of the pseudocholinesterase level
Mild 20-50% enzyme activity
Moderate 10-20% enzyme activity and
Severe <10% enzyme activity
NB: True or erythrocyte cholinesterase correlates well with clinical severity but
is not available in most centres
21. General supportive treatment
1. Assessment of airways, breathing, and circulation
Comatose or vomiting patients should be kept in lateral positioning and
consider of placement of Guedel’s airway or ET intubation.
Frequent suctioning is essential as excessive oropharyngeal and respiratory
secretions may occlude the airway.
Oxygen is needed in majority of these patients; and this can be assessed by
frequent assessment of arterial oxygen saturation.
22. 2. Decontamination
The clothes should be removed and the skin
vigorously washed with soap and water.
NB: Always remember to wear gloves so as to prevent
skin absorption of the poison.
23. 3. Gastric lavage
Should be considered in patients presenting within 1-2
hours of ingestion of poison
Risks of gastric lavage include :
Aspiration
Hypoxia
Laryngeal spasm
Administer activated charcoal 100gm(aprox. 1gm/kg) in 200-
500ml of water.
24. Specific Antidotal Treatment
Atropine
Has been cornerstone in the management of OP poisoning
Atropine only blocks muscarinic effects whereas oximes reverse
both the nicotinic and muscarinic effects
MOA: competitively at the peripheral and central muscarinic
receptors and antagonizes the parasympathetic effects of excess
Ach.
25. Target end-points for Atropine therapy
Heart rate >80/ min
Dilated pupils
Dry axillae
Systolic blood pressure >80 mm Hg
Clear chest with absence of wheeze
26. HOW MUCH ATROPINE???
Initial bolus of 3-5 ampoules of atropine (each
ampoule containing 0.6 mg)
Subsequent doses doubled every 5 minutes until
atropinization is achieved
When the patient achieves most of (at least 4 out of 5)
the target end-points for atropine therapy i.e. fully
atropinized
28. INFUSION ATROPINE
10% of initial atropinizing dose per hour for first 24 hours
Reduce by 20-30% every day of initial dose
Tapper in this manner for 5 days
Reduce dose if features of toxicity develop
29. What if you give too much ATROPINE?
Hot as Hell
Blind as a Bat
Red as a Beet
Dry as a Bone
Mad as a hatter
That means hyperthermia, tachycardia, tremer,
restlessness, confusion, agitation, seizures
30. Oximes
Oximes work by reactivating acetylcholinesterase that has been
bound to the OP molecule
Eg. Pralodoxime(frequently used), obidoxime
WHO recommended pralidoxime dose of
30 mg/kg bolus iv over 10-20 minutes followed by continuous
infusion of 8-10 mg/kg/hour till atropine no longer required or 7 days
(whichever later)
Not recommended for carbamates
31. Benzodiazepines:
Diazepam and other benzodiazepines are widely used
for the treatment of OP induced seizures and
restlessness and agitation
32. Pregnancy
ingested OP insecticides during the second or third
trimester of pregnancy have been treated successfully
with atropine and pralidoxime
33. Diet
Nill per oral during atropinization
Once peristalsis sounds are heard start oral fluids and
gradually shift to soft food
34. Newer forms of therapies in OP
poisoning
Sodium bicarbonate
Adrenergic receptor α2 agonists like clonidine
Magnesium sulphate
Fresh frozen plasma
Antioxidants
Organophosphorus hydrolases
Galyclidine (NMDA receptor antagonist)
