Dipyridyl Herbicides (paraquat/diquat)

Question 1

Is paraquat RUP (restricted use pesticide) or GUP (general use pesticide)? Is diquat RUP or GUP?

Answer 1

Paraquat = restricted use pesticide –> more toxic

Diquat = general use pesticide –> less toxic

Question 2

If paraquat is sprayed at 0.5 lb/acre for agricultural use, what is the mg/kg (body weight) toxicity?

Answer 2

3.5 mg/kg body weight

1lb/acre = 7 mg/kg body weight

Question 3

What are common sources of Dipyridyl herbicide poisonings?

Answer 3

Ingestion of concentrates

Malicious poisoning

Question 4

Which herbicide is better absorbed, paraquat or diquat?

Answer 4

Paraquat

Diquat is not very lipid soluble - poor absorption - less toxic

Question 5

What pH environments will destroy paraquat/diquat?

Answer 5

alkaline pH

these are stable in neutral or acidic environments

Question 6

What does paraquat bind strongly to in nature? How can this affect treatment?

Answer 6

Binds strongly to soil - could potentially be used as an adsorbent - but activated charcoal is even more effective

Question 7

T/F: Paraquat is caustic to mucus membranes

Answer 7

TRUE

Question 8

What percentage of paraquat will be absorbed in the GIT, why?

Answer 8

only 5-10% bc it is not very lipid soluble

Question 9

What animals are susceptible to paraquat poisoning? What is the toxic dose, and how is it categorized?

Answer 9

All animals are susceptible (cats, dogs, pigs, sheep, humans)

LD50 = 25 - 75 mg/kg

~ highly toxic (1-50 mg/kg)

Question 10

What deficiencies may increase the toxicity of paraquat? Why?

Answer 10

animals that are deficient in selenium & vitamin E, and glutathione

These are antioxidants- so without them or decreased amount can lead increase tissue damage

Question 11

What treatment can potentially increase tissue damage due to paraquat toxicosis?

Answer 11

Oxygen therapy

BUT - if the patient is in critical need, you should use it (just know it could increase tissue damage)

Question 12

Daily oral exposure to ___ppm paraquat causes chronic toxicity and death in dogs

Answer 12

170 ppm

Question 13

T/F: Paraquat is absorbed well by the GIT

Answer 13

FALSE

only small amounts are absorbed via the GIT and skin

Question 14

What is the distribution of paraquat in the body?

Answer 14

distributed all over the body but achieves the highest concentration in the lungs

Question 15

How is paraquat excreted?

Answer 15

Mainly unchanged in the urine within 24 hours (minimal metabolism)

Question 16

What is the MOA of paraquat?

Answer 16

tissue damage all over the body and severe damage in the lungs

production of free radicals that will cause oxidative cell membrane damage, degeneration, and necrosis

Question 17

What clinical signs will be noted with acute paraquat poisoning?

Answer 17

EARLY (first 24hr): usually limited to GI signs: vomiting, anorexia, depression (may resolve before resp. signs begin)

DELAYED (2-7days): this is the usual time frame of death for patients - respiratory signs: tachypnea, dyspnea, harsh resp. sounds, cyanosis, reduced pulmonary compliance

***sometimes signs aren’t seen until 3 days after exposure

Question 18

What clinical signs will be seen in a patient who survives paraquat toxicosis?

Answer 18

(subacute or chronic toxicosis: after 7 days up to 3 weeks)

Respiratory signs associated with progressive pulmonary fibrosis

patients will survive if not each lung lobe was affected or if they were not severely affected

Question 19

What lesions are associated with paraquat poisoning?

Answer 19

Pulmonary edema, congestion, hemorrhage, fibrosis, and failure of the lung to collapse
Lingual ulcers
Liver, Kidney, Spleen - enlarged/congested

“hepatosization” of the lung - grossly resembles the liver

Question 20

What are the chances of a positive chemical analysis on a urine sample that was collected 48 hours after paraquat ingestion?

Answer 20

slim to none

Urine samples may be negative after 48 hours from exposure

so by the time you see clinical signs and take samples - they likely will test negative

Question 21

What diagnostics could prove helpful in confirming lung lesions in the live patient suspected of ingesting paraquat?

Answer 21

Radiographs

Question 22

How is a paraquat poisoning diagnosis made?

Answer 22

History + clinical signs (GI in the first 24hr + Resp), Lesions, and laboratory diagnostics

Question 23

What would be differential diagnoses for paraquat poisoning?

Answer 23

Pneumonia
Inhalant toxicants like nitrous oxide and ammonia
Some rodenticides

Question 24

How are patients with paraquat poisoning treated?

Answer 24

Emetics (only before severe GI damage)
ACTIVATED CHARCOAL
Bentonite or Fuller’s earth choice PO
Parafin oil cathartics (more gentle than saline)

IVF, Hemodialysis/peritoneal dialysis

Antioxidants (better for prevention) - orgotein, acetylcystein, ascorbic acid, niacin or riboflavin

Question 25

What is the prognosis of paraquat poisoning

Answer 25

Guarded or grave

*only chance is if treatment is started within 24 hours of exposure (which is unlikely since resp signs aren’t noted for at least 48 hours)