Tox: pesticides, insecticides, rodenticides

Question 1

Source of organophosphate/carbamate exposure

Answer 1

Insecticides used extensively in agriculture and commercial applications.

Question 2

Difference between organophosphates and carbamates in terms of binding to cholinesterases

Answer 2

Organophosphates bond to cholinesterases and ‘age’ such that binding becomes irreversible over time

Question 3

MOA of tox of organophos/carbamates

Answer 3

Inhibit cholinesterases –> increase in synaptic acetylcholine –> inc activity at nicotinic/muscarinic receptors.

Carbamates: transient cholinesterase binding (minutes-hrs).
Organophosphates: undergo aging resulting in irreversible binding of cholineterases.

Question 4

SS of organophos/carbamate toxicity

Answer 4

Cholinergic (muscarinic) toxidrome.
Sympathomimetic excess from preganglionic nicotinic receptor stimulation.
Muscle weakness, fasciculations, paralysis from nicotinic excess at the NMJ.
AMS, seizures.

Question 5

Antidote to organophos/carbamate

Answer 5

1) Atropine: for unstable brady, excessive secretions (endpoint is drying of airway secretions).
2) Pralidoxime (2-PAM) for ORGANOPHOS: to reactivate inhibited cholinesterase in organophos poisoning prior to ‘aging.’

Question 6

Typical dosing of atropine in organophos/carbamate poisoning

Answer 6

Very high doses: 0.5-2mg IV initially with doubling of dose q5min until airway secretions dry

Question 7

What is a ‘superwarfarin’?

Answer 7

Found in most home rodenticide products. E.g. brodifacoum.
Act similar to warfarin by inhibiting vit K dependent clotting factors (10,9,7,2) however, duration of anticoagulation may extend x weeks.

Question 8

Onset of lab abnormalities and duration of activity of superwarfarins

Answer 8

Lab abnormalities occur after 1-2days, may last for weeks.

Question 9

At what point can a normal INR/PT exclude superwarfarin toxicity

Answer 9

If PT/INR normal 48hrs post ‘superwarfarin’ ingestion, there is NO toxicity

Question 10

Tx of suprawarfarin toxicity

Answer 10

1) If elevated INR, give vitamin K (may require high doses for prolonged periods if large suprawarfarin ingestion).
2) Acute bleeding: FFP, cyroppt or PCC to reverse anticoagulation

Question 11

What is the potential harm of giving prophylactic vitamin K in suprawarfarin toxicity

Answer 11

May masking impending INR elevation and not allow it to be accurate future marker of anticoagulation

Question 12

What is strychnine

Answer 12

Rodenticide with significant human toxicity. Largely replaced by superwarfarins in home products.

Question 13

MOA of strychnine

Answer 13

Inhibits glycine receptors in the spinal cord resulting in uncontrolled muscle contraction.

Question 14

SS of strychnine poisoning

Answer 14

Rapid onset involuntary muscle contraction, opisthotonus, hyperreflexia, clonus, trismus. Usually within 15-30 min of ingestion.
Mental status NOT affected.

Question 15

Tx of strychnine poisoning

Answer 15

Benzos/barbiturates to relieve excess muscle activity.

Severe cases require intubation and neuromuscular blockade.