New treatment regimens in organophosphate (diazinon) and
carbamate (methomyl) insecticide - induced toxicoses in fowl
Alan Shlosberg, Michel Bellaiche, Vera Hanji, Evgenia Ershov
The Kimron Veterinary Institute, P.O. Box 12, 50250 Bet Dagan, Israel
Abstract. The objective of this work was to determine optimal treatment regimens for
organophosphate (OP) or carbamate insecticide toxicoses in fowl using the antidotes atropine
sulfate and pralidoxime chloride (2-PAM). Broiler chicks in treatment groups, each comprising 3
replicates of 6-7 birds / replicate were gavaged on a body weight (BW) basis with the OP and
carbamate insecticides, diazinon and methomyl, respectively, at lethal dosages. Treatment groups
were injected with either or both of the antidotes at various dosages as soon as clinical signs
appeared. Birds appearing healthy 24 hours thereafter were regarded as having been treated
successfully. At a dosage of 100 mg/kg BW, atropine was mildly toxic and at 200mg/kg 2-PAM
was severely toxic (but not lethal), whereas at dosages of 50 and 100 mg/kg BW, respectively, the
antidotes were at their most potent. With diazinon, atropine was only partially effective (12/20
survivors), whereas 2-PAM was extremely efficacious (20/20 survivors); the combination of the 2
antidotes at 2 dosages was slightly less effective (19/20 survivors) than 2-PAM alone. With
methomyl, atropine was largely successful (18/20 survivors), whereas 2-PAM was mostly
unsuccessful (10/20 survivors); the combination at a high dosage was less effective (15/20
survivors) than atropine alone, but at a low dosage the combination was the most successful
(20/20 survivors). These results indicate that anticholinesterase insecticide toxicoses in fowl
should not be treated according to textbook recommendations, and antidotal dosage with atropine
should be up to 100 times greater than is commonly recommended. The specific cause of the
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toxicoses should be determined before treatment can be given, but as this is often unknown, a
combination of antidotes may be the optimal treatment protocol.
One of the most important aims of veterinary medicine is to successfully treat sick animals, and
treatment is usually specific for an explicit diagnosed cause. With regard to toxicoses, this is not
easily performed as the dosage of a substance determines its toxicity and accordingly virtually
everything in the environment of animals may be toxic. Of these thousands of substances with
potential toxicity to domestic and wild animals, very few in fact have a specific antidotal
treatment (1). However, it is fortunate that probably the most potentially hazardous group of
compounds, the anticholinesterase organophosphate (OP) and carbamate insecticides, has specific
antidotes. Due to the extremely common use of these insecticides for ectoparasite control on pet
and farm animals, their use in household and public health, and on field crops and fruit trees, and
even maliciously, it is not surprising that toxicoses are often reported in domestic and wild
animals (1-4). Signs of poisoning due to OP and carbamate insecticide toxicoses typically
develop very rapidly, and treatment should be instigated within minutes of exposure if mortality
is to be minimized (1-4). Treatment regimens of such toxicoses in man comprise atropine sulfate
administered to counteract muscarinic effects, particularly the life - threatening anoxia, in
conjunction with oximes, such as pralidoxime chloride (2-PAM), which speed up the breaking of
the insecticide - acetylcholinesterase bond (5-6). Although OP and carbamate insecticides have a
similar mode of action, it has been noted that toxicity induced by the least toxic of the carbamate
insecticides, carbaryl, should not be treated with oximes, and is even contraindicated, actually
enhancing the inhibition of cholinesterases (6-7).
Limited research has been conducted to
examine how toxicoses caused by the more modern, more toxic, carbamate insecticides such as
methomyl, aldicarb and carbofuran react to treatment with oximes (7). Despite the known
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toxicity of these insecticides in animals, their common use and not infrequent toxicoses, very
little research has been conducted in recent times on the efficacy of treatment regimens in
domestic and wild animals, in particular in avian species.
With regard to the dosage for atropine in birds, very few guidelines could be found, but
dosages of 0.1-0.2 mg/kg were quoted (2,8), in contrast to higher dosages (0.2-0.5 mg/kg) for
other domestic animals (9). With regard to treatment with oximes, most of the standard veterinary
textbooks are not updated with regard to any domestic animal. The use of oximes for treatment of
carbamate toxicosis in animals is quoted as, “...of no benefit in treatment, although they may
cause no harm” (1),
“...not recommended” (10),
“...ineffective” (12,13),
“...ineffective, or even contraindicated” (14), “...at best unreliable and
at worst contraindicated” (15),
“...omitting use of 2-PAM” (11),
“... contraindicated” (16), “...not effective and may worsen the
animal’s condition” (17), “not with oximes, which may enhance toxicity” (3).
The senior author has experience of such toxicoses which casts doubts on the veracity of
atropine-based treatment regimens for avian species. Treatment of diazinon (an OP insecticide) poisoned geese, following a field case, showed that atropine was not very effective, whereas 2PAM (iodide salt) was dramatically efficacious (18); other non-antidotal husbandry factors for
OP - poisoned birds were also extremely important (19). Monocrotophos (an OP insecticide) poisoned feral raptors were also not efficaciously treated with atropine, whereas 2-PAM (iodide
salt) was again successful (20); differences in species response to 2-PAM treatment were noted.
A feral Griffon vulture exposed dermally to parathion (an OP insecticide) also showed a similar
poor response to atropine and an excellent, albeit transient, response to 2-PAM (21).
These
works and the paucity of data on avian species led this group to a preliminary work in Japanese
quail (Coturnix coturnix japonica), where it was found that atropine at recommended dosages had
no effect on the course of OP or carbamate toxicoses (22).
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This present work examined the practical treatment, with atropine sulfate, 2-PAM, or a
combination of them both, in toxicoses induced by diazinon (as a very commonly used
representative of OP insecticides) or methomyl (as a commonly used representative of the more
modern, more toxic, carbamate insecticides) in broiler chicks, as a model for avian species.
Materials and Methods
The OP examined was technical diazinon (Dizictol, Machteshim, Beer Sheva, Israel) and
the carbamate was technical methomyl (Lannate 20, Dupont, Paris, France). Aliquots of
insecticide diluted in distilled water were given by gavage using a pipette, on a body weight (BW)
basis, to 14-20 days old Arbor Acres broiler chicks. The acute oral LD50 was determined to be 3.0
mg/kg BW for diazinon and 41mg/kg BW for methomyl. In the treatment studies, insecticides
were administered at a lethal dosage of 10 mg/kg body weight for diazinon and 60 mg/kg for
methomyl. All birds so dosed developed signs within 20-70 minutes for diazinon and 3-15
minutes with methomyl, and died within one hour thereafter. Treatment was given when the first
clinical signs (salivation, tremor, and recumbency) appeared. Each treatment regimen was
examined in 20 birds, comprising 3 replicates of 6-7 birds each; in order to get reliable results,
replicates were examined on different days, with different solutions, and in several hatches of
birds. Atropine sulfate (Atropine injection, Vitamed, Bat Yam, Israel) was initially administered
intramuscularly into the pectoral muscles at various low dosages, starting at 0.5 mg/kg BW (the
recommended therapeutic dosage for most species), but when it was seen that it had no
therapeutic effect on the poisoned chicks, it was then injected into groups of untreated chicks at
various increasing dosages. It was noted that even at up to 50 mg/kg BW no adverse short or long
term effect was seen. Pralidoxime chloride (2-Pyridinealdoxime methochloride, Aldrich,
Milwaukee, Wisconsin) dissolved in sterile saline was administered intramuscularly into the
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pectoral muscles therapeutically at dosages of 50 and 100 mg/kg BW. Combined treatment
protocols comprised simultaneous, separate, administration of atropine and 2-PAM. The
qualitative determination of atropine esterase activity in blood plasma was determined by the
microhematocrit tube technic (23) in normal animals, comprising 5 broilers aged 2 weeks, 5 adult
white laboratory rabbits and 5 Israeli-Friesian calves.
Results
Dosage of antidotes
Antidotal data are shown in Table 1. In non-poisoned chicks, atropine at up to 50 mg/kg
BW had no apparent deleterious effect, whereas at 100 mg/kg, 2 of 20 birds died. In non-poisoned
chicks, 2-PAM at up to 100 mg/kg BW had no apparent deleterious effect, whereas at 200 mg/kg,
several birds showed severe signs of toxicity (depression, recumbency) for several hours, but no
birds died. Combined treatment protocols (atropine at 25 mg/kg + 2-PAM at 50 mg/kg, or
atropine at 50 mg/kg + 2-PAM at 100 mg/kg) were given without apparent effect, whereas a
higher dosage of atropine at 100 mg/kg + 2-PAM at 200 mg/kg culminated in an apparent
toxicity, with 3 of 20 birds dying.
Efficacy of antidotes
Diazinon toxicosis. Treatment with atropine at a dosage of 50 mg/kg BW was partially
efficacious, with 12 of 20 birds surviving (Table 1). With 2-PAM at 100 mg/kg BW, all 20
treated chicks survived. Combined treatment protocols (atropine at 25 mg/kg + 2-PAM at 50
mg/kg, or atropine at 50 mg/kg + 2-PAM at 100 mg/kg) culminated in slightly reduced efficacy,
with 19 of 20 birds recovering.
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Methomyl toxicosis. Treatment with atropine at a dosage of 50 mg/kg BW was largely
efficacious, with 18 of 20 birds surviving (Table 1). Atropine at a dosage of 25 mg/kg BW
resulted in the same number of survivors, but clinical signs were much slower to dissipate. With
2-PAM at 100 mg/kg BW, only 10 of 20 treated chicks survived. A combined treatment protocol
of atropine at 25 mg/kg + 2-PAM at 50 mg/kg resulted in complete recovery in all treated birds. A
higher dosage (atropine at 50 mg/kg + 2-PAM at 100 mg/kg) culminated in a reduced antidotal
efficacy, with 15 of 20 birds recovering.
Atropine esterase activity. A visual estimation of the activity of blood atropine esterase
showed high activity in rabbit blood, virtually no activity in cattle blood, and intermediate activity
in the broiler blood.
Discussion
The aim of this work was to investigate whether the oft-quoted guidelines for treatment of
OP and carbamate insecticide toxicosis are valid. It can be categorically stated that efficacious
treatment in broiler chicks is quite different.
The dosage of atropine quoted for most domestic animals, 0.5 mg/kg BW, is that used in
children (24). There is however a wide variation in sensitivity to atropine between species, and
whereas man and pigs are very sensitive, cattle, horses and chickens are less so, whereas sheep
and rabbits are resistant (25). This present work showed that dosages of atropine many times
higher than the recommended dosages for birds and other species were completely ineffective as a
treatment, and even 50 mg/kg BW was non-toxic to broiler chicks. At 50 mg/kg BW it was a
good, but not completely efficacious treatment (90% survival) with methomyl, but was
considerably inferior with diazinon (60% survival). It should be remembered that very young
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animals may have functionally immature MFO systems (26) to detoxify many toxicants, and so
this model in 2-3 week old birds may be more sensitive (to the antidote and to the toxicant) than
adult birds. A probable explanation for the very high dosages required for physiological effects
may be the presence of an hydrolytic enzyme in the blood capable of metabolizing atropine. This
so-called atropine esterase has been shown to be present in some strains of rabbit (27), but not in
laboratory mice (23). The results of our preliminary trial showed that broilers used in this trial
had levels of an atropine-metabolizing enzyme in their blood intermediate between the high levels
in laboratory rabbits and the apparently non-existent levels in cattle. It would be useful to develop
and use quantitative methods for determination of such blood enzymes in different, including
feral, avian species, in order to further evaluate potential antidotal efficacy of atropine.
One aim of the work with 2-PAM was to test whether the warnings against its use with
carbamates, so replete in the veterinary literature (11-17) despite the probably unheeded
admonition (28) against this common view, were valid. Many other oximes have been
investigated in the treatment of organophosphate toxicoses (29), but 2-PAM was chosen as being
representative as it is easily available (although not approved by the FDA for animal treatment in
the USA) and has been the most used for human treatment (24). Another oxime, obidoxime
chloride, is preferred over 2-PAM in most European countries, Canada and Israel for use in man
(30), but this was found to be too toxic for use in geese (18), and so was not tested in this work.
In the treatment of the carbamate toxicosis in the present study, it was only partially successful
(50% survival), and although certainly not ineffective or harmful, it cannot be recommended as a
sole treatment. In contrast, the 2-PAM treatment of OP toxicosis was perfect (100% survival).
Similar efficacy against OP with only 2-PAM was reported elsewhere (2), in dogs. The effect of
oximes in augmenting carbaryl toxicity is probably due to increased carbamylation (inhibition) of
acetylcholinesterase caused by oximes (28). In vitro experiments showed that pralidoxime
decreased the rate of carbamylation of 16 insecticidal carbamates, whereas a modest (deleterious)
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increase in carbamylation was seen in only 3 such carbamates, one of which was carbaryl (28).
These results suggested that the majority of carbamates can be logically treated with oximes.
The combination of the two antidotes for diazinon toxicosis was slightly less efficacious
(95% survival) than 2-PAM alone; this would indicate that atropine reduces the efficacy of 2PAM. With methomyl, the low dosage combination, atropine at 25 mg/kg + 2-PAM at 50 mg/kg,
was even better (100% survival) than the good treatment with atropine alone (90% survival),
indicating that 2-PAM, rather ineffective by itself (50% survival), improved the efficacy of
atropine. At twice this dosage, the combination was less effective (75% survival) than atropine by
itself or the low dosage combination; presumably this was due to the increased 2-PAM dosage.
Clinical signs of OP and carbamate toxicoses are usually indistinguishable, and in the
field, where speedy treatment is essential and where the specific compound or group is often
unknown, a logical treatment should comprise a combination of the 2 antidotes, particularly in the
light of our present findings with regard to optimal treatment of each type of insecticide. With
regard to broiler chickens, such a combination would be atropine at 25 mg/kg BW + 2-PAM at 50
mg/kg BW.
A preliminary work (22) in Japanese quail (Coturnix coturnix japonica) with the same
insecticides, and a later work with the antidotes at other dosages (Shlosberg et al, unpublished
data) showed similar findings to the present work. Diazinon toxicosis was treated well with 2PAM given twice in a 6 hour period and an effective treatment for methomyl toxicosis was
achieved with atropine at 50 mg/kg BW. Quail were also refractory to high doses of atropine. In
order to extend this work to the efficacious treatment of potential toxicoses from such insecticides
in wild birds, it would be very worthwhile to test and quantify many wild avian species for the
presence of atropine - metabolizing enzymes in their blood. Such testing would not require
killing birds and could be carried out concomitantly with, for instance, banding wild birds.
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Table 1. Treatment protocols and their efficacy in broiler chicks poisoned
by organophosphate (diazinon) and carbamate (methomyl) insecticides
Survivors (of 20 birds)
Drug and dosage (mg/kg BW)
Diazinon
Methomyl
Control
Antidote untreated*
0
0
20
Atropine 25
...
18
20
Atropine 50
12
18
20
Atropine 100
...
...
18
2-PAM 100
20
10
20
2-PAM 200
...
...
20**
Atropine 25
+ 2-PAM 50
19
20
20
Atropine 50
+ 2-PAM 100
19
15
20
Atropine 100 + 2-PAM 200
...
...
17
* Data from lethal dose estimations
** No mortality, but showed signs of toxicity
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