Parasympathomimetics or Cholinergic Drugs By Baasir Umair

PARASYMPATHOMIMETICS Dr. BAASIR UMAIR

CHOLINERGIC TRANSMISSION
 Acetylcholine (ACh) is a major neurohumoral transmitter at autonomic,
somatic as well as central sites.

SYNTHESIS, STORAGE AND
DESTRUCTION OF ACH

NEUROTRANSMISSION AT
CHOLINERGIC NEURONS

Two Toxins Interfere With Cholinergic Transmission By Affecting
Release

BOTULINUM
TOXIN
Clinical uses:
•Blepharospasm, spastic cerebral palsy,
strabismus, spasmodic torticollis,
nystagmus, hemifacial spasm, post stroke
spasticity, spasmodic dysphonia, axillary
hyperhydrosis, etc.
•It is increasing being employed as beauty
treatment by removal of age-related facial
wrinkles.
•ADRS:
•However, its incorrect injection or overdose
can be dangerous; ptosis, diplopia, facial
swelling, dry mouth, dysphagia, dysarthria,
muscular weakness and even respiratory
paralysis has occurred
• Botulinum toxin A and B are
highly potent exotoxins
produced by Clostridium
botulinum that are responsible
for ‘botulism’ (a type of food
poisoning).

BLACK WIDOW SPIDER TOXIN
α-Latrotoxin
α-Latrotoxin is a presynaptic neurotoxin isolated from the venom of the black
widow spider Latrodectus tredecimguttatus. It exerts toxic effects in the
vertebrate central nervous system by depolarizing neurons, by increasing
[Ca2+
]i and by stimulating uncontrolled exocytosis of neurotransmitters from
nerve terminals.

CHOLINESTERASE:
Immediately after release, ACh is hydrolyzed by the enzyme cholinesterase
and choline is recycled.
1. A specific (Acetylcholinesterase—AChE or true cholinesterase)
2. A nonspecific (Butyrylcholinesterase—BuChE or pseudocholinesterase)
These two types of enzyme occurs in the body; important differences
between these two types of the enzyme are given in Table
The purpose is to degrade the aacetylcholine.

CHOLINOCEPTORS:
TYPE 1 MUSCARINIC RECEPTOR

CHOLINOCEPTORS:
TYPE 2 NICOTINIC RECEPTOR

ACTIONS:
( ACH AS PROTOTYPE)
A. Muscarinic actions:
1. Heart
2. Blood vessels
3. Smooth muscle
4. Glands
5. Eye
B. Nicotinic actions
1. Autonomic ganglia
2. Skeletal muscles:
C. CNS actions

ACETYLCHOLINE
Acetylcholine [ah-see-teel-KOE-leen] is a quaternary ammonium compound
that cannot penetrate membranes.
 Although it is the neurotransmitter of parasympathetic and somatic nerves
as well as autonomic ganglia, it lacks therapeutic importance because of its
multiplicity of actions (leading to diffuse effects) and its rapid inactivation by
the cholinesterases.

A. MUSCARINIC ACTIONS
1. Heart:
ACh hyperpolarizes the SA nodal cells and decreases their rate of diastolic
depolarization.
As a result, rate of impulse generation is reduced—bradycardia or even cardiac
arrest may occur.
At the A-V node and His-Purkinje fibres refractory period (RP) is increased and
conduction is slowed: P-R interval increases and partial to complete A-V block may
be produced.
The force of atrial contraction is markedly reduced and RP of atrial fibres is
abbreviated.

Due to nonuniform vagal innervation, the intensity of effect on RP and
conduction of different atrial fibres varies— inducing inhomogeneity and
predisposing to atrial fibrillation or flutter.
Ventricular contractility is also decreased but the effect is not marked.
The cardiac muscarinic receptors are of the M2 subtype.
2. Blood vessels:
 All blood vessels are dilated, though only few (skin of face, neck, salivary
glands) receive cholinergic innervation.
Fall in BP and flushing, especially in the blush area occurs.

Muscarinic (M3) receptors are present on vascular endothelial cells:
vasodilatation is primarily mediated through the release of an endothelium
dependent relaxing factor (EDRF) which is nitric oxide (NO).
The PLc-IP3/DAG pathway activates endothelial NO synthase through the
Ca+-Calmodulin mechanism.
When the endothelium is damaged by disease, ACh can diffuse to the
vascular smooth muscle and cause vasoconstriction via M3 receptors located
on their plasma membrane.
Stimulation of cholinergic nerves to the penis causes erection by releasing
NO and dilating cavernosal vessels through M3 receptors.
However, this response is minimal with injected cholinomimetic drugs.

3. Smooth muscle:
Smooth muscle in most organs is contracted (mainly through M3
receptors). Tone and peristalsis in the gastrointestinal tract is increased and
sphincters relax abdominal cramps and evacuation of bowel.
Peristalsis in ureter is increased; The detrusor muscle contracts while the
bladder trigone and sphincter relaxes voiding of bladder.
 Bronchial muscles constrict, asthmatics are highly sensitive
bronchospasm, dyspnoea, precipitation of an attack of bronchial asthma.
4. Glands:
 Secretion from all parasympathetically innervated glands is increased via
M3 and some M2 receptors: sweating, salivation, lacrimation, increased
tracheobronchial and gastric secretion.
The effect on pancreatic and intestinal glands is not marked. Secretion of
milk and bile is not affected

5. Eye:
 Contraction of circular muscle of iris miosis.
 Contraction of ciliary muscle, spasm of accommodation, increased outflow
facility, reduction in intraocular tension (especially in glaucomatous patients)

B. NICOTINIC ACTIONS
1. Autonomic ganglia:
Both sympathetic and parasympathetic ganglia are stimulated. This effect is
manifested at higher doses.
High dose of ACh given after atropine causes tachycardia and rise in BP due to
stimulation of sympathetic ganglia and release of catecholamines.
2. Skeletal muscles:
 Iontophoretic application of ACh to muscle endplate causes contraction of the
fibre.
Intraarterial injection of high dose can cause twitching and fasciculations, but i.v.
injection is generally without any effect (due to rapid hydrolysis of ACh)

C. CNS actions:
 ACh injected i.v. does not penetrate blood-brain barrier and no central
effects are seen. However, direct injection into the brain produces arousal
response followed by depression.
 Cholinergic drugs which enter brain produce complex behavioral and
neurological effects.

Interactions:
Anticholinesterases potentiate ACh
markedly, methacholine to less extent and
have only additive action with carbachol
or bethanechol, depending upon the role
of ChE in the termination of action of the
particular choline ester.
Atropine and its congeners competitively
antagonize muscarinic actions.
Adrenaline is a physiological antagonist
Uses:
Choline esters are rarely, if ever,
clinically used.
ACh is not used because of
evanescent and nonselective action.
Methacholine was occasionally used
to terminate paroxysmal
supraventricular tachycardia but is
obsolete now

BETHANECHOL
Bethanechol [be-THAN-e-kole] is an unsubstituted carbamoyl ester,
structurally related to Ach.
 It is not hydrolyzed by AChE due to the esterification of carbamic acid,
although it is inactivated through hydrolysis by other esterases.
It lacks nicotinic actions (due to the addition of the methyl group) but does
have strong muscarinic activity. Its major actions are on the smooth musculature
of the bladder and GI tract.
It has about a 1-hour duration of action.

Actions:
Bethanechol directly stimulates
muscarinic receptors, causing
increased intestinal motility and
tone.
 It also stimulates the detrusor
muscle of the bladder, whereas the
trigone and sphincter muscles are
relaxed. These effects produce
urination
2. Therapeutic applications:
 In urologic treatment, bethanechol
is used to stimulate the atonic
bladder, particularly in postpartum or
postoperative, nonobstructive
urinary retention.
 Bethanechol may also be used to
treat neurogenic atony as well as
megacolon.
Adverse effects:
Bethanechol causes the effects of generalized cholinergic stimulation.
 These include sweating, salivation, flushing, decreased blood pressure, nausea,
abdominal pain, diarrhea, and bronchospasm.
 Atropine sulfate may be administered to overcome severe cardiovascular or
bronchoconstrictor responses to this agent.
Dose: 10–40 mg oral, 2.5–5 mg s.c

CARBACHOL
(CARBAMYLCHOLINE)
Carbachol [KAR-ba-kole] has both
muscarinic and nicotinic actions.
Like bethanechol, carbachol is an
ester of carbamic acid and a poor
substrate for AChE.
It is biotransformed by other
esterases, but at a much slower rate.

Actions:
Carbachol has profound effects on both
the cardiovascular and GI systems because
of its ganglion-stimulating activity, and it
may first stimulate and then depress these
systems.
It can cause release of epinephrine from
the adrenal medulla by its nicotinic action.
 Locally instilled into the eye, it mimics
the effects of ACh, causing miosis and a
spasm of accommodation in which the
ciliary muscle of the eye remains in a
constant state of contraction.
Therapeutic uses:
Because of its high potency, receptor
nonselectivity, and relatively long
duration of action, carbachol is rarely
used therapeutically except in the eye
as a miotic agent to treat glaucoma by
causing pupillary contraction and a
decrease in intraocular pressure.
Adverse effects:
At doses used ophthalmologically, little
or no side effects occur due to lack of
systemic penetration (quaternary
amine).

CHOLINOMIMETIC
ALKALOIDS
It is obtained from the leaves of Pilocarpus microphyllus and other species.
 It has prominent muscarinic actions and also stimulates ganglia—mainly
through ganglionic muscarinic receptors.
The alkaloid pilocarpine is a tertiary amine and is stable to hydrolysis.
 Compared with ACh and its derivatives, it is far less potent but is uncharged
and can penetrate the CNS at therapeutic doses.
 Pilocarpine exhibits muscarinic activity and is used primarily in
ophthalmology.

• Pilocarpine is used to treat glaucoma and is the drug of choice for emergency
lowering of intraocular pressure of both open-angle and angle-closure glaucoma
• It is a third-line drug in open angle glaucoma folowing
darzolamide and timilol, however the later two are not
suitable for emergency condition.
• Applied to the eye, it penetrates cornea and promptly
causes miosis, ciliary muscle contraction and fall in
intraocular tension lasting 4–8 hours.
• Though it can be used as a sialogogue, no
oral preparation is available
• Pilocarpine is used only in the eye as 0.5– 4% drops.

OTHER USES:
The drug is beneficial in promoting
salivation in patients with xerostomia
resulting from irradiation of the head and
neck.
Sjögren syndrome, which is characterized
by dry mouth and lack of tears, is treated
with oral pilocarpine tablets and
cevimeline, a cholinergic drug that also has
the drawback of being nonspecific.
Adverse effects:
 Pilocarpine can cause blurred
vision, night blindness, and brow
ache.
Poisoning with this agent is
characterized by exaggeration of
various parasympathetic effects,
including profuse sweating
(diaphoresis) and salivation.
The effects are similar to those
produced by consumption of
mushrooms of the genus Inocybe.
Parenteral atropine, at doses that
can cross the blood–brain barrier, is
administered to counteract the
toxicity of pilocarpine

Muscarine:
• It occurs in poisonous mushrooms Amanita muscaria and Inocybe species and
has only muscarinic actions.
• It is not used therapeutically but is of toxicological importance.

Mushroom poisoning:
• Depending on the toxic principle present in the particular species, at least 3 types of
mushroom poisoning is known.
Muscarine type (Early mushroom poisoning):
• Due to Inocybe and related species. Symptoms characteristic of muscarinic actions
appear within an hour of eating the mushroom, and are promptly reversed by atropine.
Hallucinogenic type:
• It is due to muscimol and other isoxazole compounds which are present in A. muscaria
and related mushrooms in much larger quantities than is muscarine.
• These compounds activate amino acid receptors, and block muscarinic receptors in the
brain; have hallucinogenic property. Manifestations of poisoning are primarily central.
• There is no specific treatment and atropine is contraindicated.
• Another hallucinogenic mushroom is Psilocybe mexicana whose active principle
psilocybine is a tryptaminergic (5-HT related) compound

Phalloidin type (Late mushroom poisoning):
• It is due to peptide toxins found in A. phalloides, Galerina and related species.
• These inhibit RNA and protein synthesis.
• The symptoms start after many hours and are due to damage to the
gastrointestinal mucosa, liver and kidney.
• Treatment consists of supportive measures. Thioctic acid may have some
antidotal effect.

Arecoline:
• It is found in betel nut Areca catechu and has muscarinic as well as nicotinic
actions, including those on skeletal muscle endplate.
• It also has prominent CNS effect: has been tried in dementia as an enhancer of
cognitive functions, but not found useful—has no therapeutic use

MECHANISM OF ACTION
• The anti-ChEs react with the enzyme essentially in the same way as ACh.
• The carbamates and phosphates respectively carbamylate and phosphorylate
the esteratic site of the enzyme.
• The mammalian AChE has been cloned and details of its structure as well as
mode of interaction with ACh and various anti-ChEs has been worked out.
• The active region of AChE forms a gorge which contains an anionic site
(near glutamate 334) and an esteratic site formed by serine 203, and histidine
447.
• Hydrolysis of ACh involves electrostatic attraction of positively charged N+
of ACh to the anionic site and nucleophilic attack by serine-OH which is
activated by the adjacent histidine leading to acetylation of serine.
• The acetylated enzyme reacts with water to produce acetic acid and choline.

• Whereas the acetylated enzyme reacts with water extremely rapidly and the
esteratic site is freed in a fraction of a millisecond, the carbamylated enzyme
(reversible inhibitors) reacts slowly and the phosphorylated enzyme (irreversible
inhibitors) reacts extremely slowly or not at all.
• It is noteworthy that edrophonium and tacrine attach only to the anionic site and
do not form covalent bonds with the enzyme, while organophosphates attach only
to the esteratic site forming covalent bonds.
• Reactivation of edrophonium-inhibited enzyme occurs in < 10 min, and does not
involve hydrolysis of the inhibitor, but only its diffusion—action is brief.
• The half-life of reactivation of carbamylated enzyme (about 30 min) is less than
that of synthesis of fresh enzyme protein, while that of phosphorylated enzyme (in
days) is more than the regeneration time.
• The phosphorylated enzyme may also undergo ‘aging’ by the loss of one of the
alkyl groups and become totally resistant to hydrolysis.
• Thus, apparently reversible and irreversible enzyme inhibition is obtained, though
the basic pattern of inhibitor-enzyme interaction remains the same.

PHARMACOLOGICALACTIONS
• The actions of anti-ChEs are due to
amplification of endogenous ACh.
• As such they are qualitatively similar to
those of directly acting cholinoceptor
stimulants.
• However, relative intensity of action on
muscarinic, ganglionic, skeletal muscle and
CNS sites varies among the different
agents.
Lipid-soluble agents
(physostigmine and
organophosphates) have
more marked muscarinic
and CNS effects; stimulate
ganglia but action on
skeletal muscles is less
prominent.
Lipid-insoluble agents (neostigmine and other quaternary ammonium compounds) produce more marked effect
on the skeletal muscles (direct action on muscle endplate cholinoceptors as well), stimulate ganglia, but
muscarinic effects are less prominent. They do not penetrate CNS and have no central effects.

Ganglia Local hydrolysis of ACh is less important in
ganglia: inactivation occurs partly by diffusion and
hydrolysis in plasma. Anti-ChEs stimulate ganglia
primarily through muscarinic receptors present there.
High doses cause persistent depolarization of the
ganglionic nicotinic receptors and blockade of
transmission
Ganglia:
Local hydrolysis of ACh is less important
in ganglia: inactivation occurs partly by
diffusion and hydrolysis in plasma.
Anti-ChEs stimulate ganglia primarily
through muscarinic receptors present
there.
High doses cause persistent depolarization
of the ganglionic nicotinic receptors and
blockade of transmission
CNS:
Lipophilic anti-ChEs which
penetrate into brain produce a
generalized alerting response.
Cognitive function may be
improved in Alzheimer’s
disease. However, higher
doses produce excitement,
mental confusion,
disorientation, tremors and
convulsions followed by coma
CVS:
• Cardiovascular effects are complex.
• Whereas muscarinic action would produce bradycardia and hypotension, ganglionic stimulation would
tend to increase heart rate and BP.
• Action on medullary centres (stimulation followed by depression) further complicates the picture, so
does ganglionic blockade with high doses. Thus, the overall effects are often unpredictable and depend
on the agent and its dose

Skeletal muscles:
• After treatment with antiChEs, the ACh
released by a single nerve impulse is not
immediately destroyed—rebinds to the same
receptor, diffuses to act on neighbouring
receptors and activates prejunctional fibres
repetitive firing---- twitching and
fasciculations. Force of contraction in
partially curarized and myasthenic muscles
is increased.
• Higher doses cause persistent depolarization
of endplates resulting in blockade of
neuromuscular transmission---weakness and
paralysis.
• Direct action of neostigmine and its
congeners at the muscle endplates results in
augmentation of these features.
Other effects:
These result from
stimulation of
smooth muscles and
glands of the
gastrointestinal,
respiratory, urinary
tracts and in the eye
as described for
ACh.

PHARMACOKINETICS
Neostigmine and congeners
These are poorly absorbed orally; oral
dose is 20–30 times higher than
parenteral dose. They do not
effectively penetrate cornea or cross
blood-brain barrier. They are partially
hydrolysed and partially excreted
unchanged in urine
Physostigmine:
• It is rapidly absorbed from g.i.t.
and parenteral sites.
• Applied to the eye, it penetrates
cornea freely.
• It crosses blood-brain barrier and
is disposed after hydrolysis by
ChE
Organophosphates These
are absorbed from all
sites including intact skin
and lungs. They are
hydrolyzed as well as
oxidized in the body and
little is excreted
unchanged.
Organophosphates:
These are absorbed from
all sites including intact
skin and lungs. They are
hydrolyzed as well as
oxidized in the body and
little is excreted
unchanged.

REVERSIBLE AchE
Edroponium:
• Short Acting(10-20
mints)
• Act only in periphery
• Dx of mysthenia gravis
2mg and maximum
dose upto 8-10mg
• Rapid renal elimination
Phsiostigmine:
• Intermediate acting 30
mint to 2 hrs
• Can enter to CNS
• Avert the effect of
atropine
Neostigmine:
• 30 mint to 2 hr
duration, intermediate
• Synthetic
• Poler
• Treatment of
mysthenia gravis
• Antidote for atropine
Pyridostigmine and
ambenonium:
• 3-6 hrs and 4-8 hrs,
longer acting

IRREVERSIBLE Acetyle Choline Esterase
• A number of synthetic
organophosphate compounds
have the capacity to bind
covalently to AChE.
• The result is a long-lasting
increase in ACh at all sites
where it is released.
• Many of these drugs are
extremely toxic and were
developed by the military as
nerve agents.
• Related compounds, such as
parathion and malathion, are
used as insecticides.
Mechanism of action:
Echothiophate [ek-oe-THI-oh-fate] is an
organophosphate that covalently binds via its
phosphate group at the active site of AChE.
Once this occurs, the enzyme is permanently
inactivated, and restoration of AChE activity
requires the synthesis of new enzyme
molecules.
Following covalent modification of AChE, the
phosphorylated enzyme slowly releases one of
its ethyl groups.
The loss of an alkyl group, which is called
aging, makes it impossible for chemical
reactivators, such as pralidoxime, to break the
bond between the remaining drug and the
enzyme.

Actions:
• Actions include generalized
cholinergic stimulation, paralysis of
motor function (causing breathing
difficulties), and convulsions.
• Echothiophate produces intense
miosis and, thus, has found
therapeutic use. Intraocular pressure
falls from the facilitation of outflow
of aqueous humor.
• Atropine in high dosages can reverse
many of the peripheral and some of
the central muscarinic effects of
echothiophate.
Therapeutic uses:
• A topical ophthalmic solution of the
drug is available for the treatment of
open-angle glaucoma.
• However, echothiophate is rarely
used due to its side effect profile,
which includes the risk of causing
cataracts

USES
1. As miotic:
(a) In glaucoma: Pilocarpine is the preferred miotic. The action is
rapid and short lasting (4–6 hr); 6–8 hourly instillation is required
and even then i.o.t. may fluctuate inbetween, Physostigmine
(0.1%) is used only to supplement pilocarpine
(b) To reverse the effect of mydriatics
after refraction testing.
(c) To prevent formation of adhesions
between iris and lens or iris and cornea.
2. Myasthenia gravis:
Treatment is usually started
with neostigmine 15 mg
orally 6 hourly.
Pyridostigmine is an
alternative which needs less
frequent dosing.
Diagnostic tests for myasthenia gravis:
Initially edrophonium 2 mg is injected i.v. as a test dose. If nothing untoward happens, the remaining 8 mg is injected
after 30–60 sec. In case edrophonium is not available, the test can be performed with 1.5 mg i.v. neostigmine.

USES
3. Postoperative paralytic ileus/urinary retention:
This may be relieved by 0.5–1 mg s.c. neostigmine, provided no organic obstruction is present
6. Postoperative decurarization :
Neostigmine 0.5–2.0 mg (30–50 g/kg) i.v., precede by atropine or glycopyrrolate 10 g/kg to block muscarinic
effects, rapidly reverses muscle paralysis induced by competitive neuromuscular blockers
4. Cobra bite:
Though specific
antivenom serum is the
primary treatment,
neostigmine + atropine
prevent respiratory
paralysis.
5. Alzheimer’s disease:
Characterized by progressive
dementia, AD is a neurodegenerative
disorder, primarily affecting
cholinergic neurones in the brain.
Various measures to augment
cholinergic transmission in the brain
have been tried.
The relatively cerebroselective anti-
ChEs, rivastigmine, donepezil and
galantamine are now commonly used

Other drug overdosages Tricyclic
antidepressants, phenothiazines and
many antihistaminics have additional
anticholinergic property. Overdose
symptoms and coma produced by
these drugs are partly antagonized by
physostigmine. However, it may worsen
the fall in BP and arrhythmias; use
therefore is risky. Physostigmine also
appears to have a modest nonspecific
arousal effect in CNS depression
produced by diazepam or general
anaesthetics, but use for this purpose is
rarely warranted.
7. Belladonna poisoning
Physostigmine 0.5–2 mg i.v.
repeated as required is the
specific antidote for poisoning
with belladonna or other
anticholinergics.
• It penetrates bloodbrain
barrier and antagonizes both
central and peripheral
actions. However,
physostigmine often itself
induces hypotension,
arrhythmias and undesirable
central effects.
• It is therefore employed
only as a last resort.
Neostigmine does not block
the central effect, but is less
risk
8. Other drug overdosages :
• Tricyclicantidepressants,
phenothiazines and many
antihistaminics have additional
anticholinergic property.
• Overdose symptoms and coma
produced by these drugs are partly
antagonized by physostigmine.
• However, it may worsen the fall in
BP and arrhythmias; use therefore is
risky. Physostigmine also appears to
have a modest nonspecific arousal
effect in CNS depression produced
by diazepam or general anaesthetics,
but use for this purpose is rarely
warranted.

Local muscarinic manifestations at the site of exposure (skin, eye, g.i.t.) occur
immediately.
Anticholinesterases are easily available and extensively used as agricultural
and household insecticides.
ANTICHOLINESTERASE POISONING
followed by complex systemic effects due to muscarinic, nicotinic and central actions
Followed by complex systemic effects due to muscarinic, nicotinic and central
actions

Treatment
1. Termination of further exposure to the poison— fresh air, wash the
skin and mucous membranes with soap and water, gastric lavage
according to need.
2. Maintain
patent airway,
positive pressure
respiration if it is
failing
4. Specific
antidotes
3. Supportive measures—maintain BP, hydration, control of
convulsions with judicious use of diazepam.

(a) Atropine:
• It is highly effective in counteracting the muscarinic symptoms, but
higher doses are required to antagonize the central effects.
• It does not reverse peripheral muscular paralysis which is a nicotinic
action.
• All cases of anti-ChE (carbamate or organophosphate) poisoning must
be promptly given atropine 2 mg i.v. repeated every 10 min till dryness
of mouth or other signs of atropinization appear (upto 200 mg has been
administered in a day).
• Continued treatment with maintenance doses may be required for 1–2
weeks

(b) Cholinesterase reactivators
Oximes are used to restore
neuromuscular transmission
only in case of
organophosphate anti-ChE
poisoning.
• The phosphorylated ChE
reacts very slowly or not at
all with water.
• However, if more reactive
OH groups in the form of
oximes (generic formula
R–CH = N–OH) are
provided, reactivation
occurs more than a million
times faster
Pralidoxime (2-PAM) has a positively charged
quaternary nitrogen: attaches to the anionic site of the
enzyme which remains unoccupied in the presence of
organophosphate inhibitors. Its oxime end reacts with
the phosphorus atom attached to the esteratic site: the
oxime-phosphonate so formed diffuses away leaving
the reactivated ChE.
Pralidoxime is ineffective as an antidote to
carbamate anti-ChEs (physostigmine,
neostigmine, carbaryl, propoxur) in which case
the anionic site of the enzyme is not free to
provide attachment to it. It is rather
contraindicated in carbamate poisoning, because
not only it does not reactivate carbamylated
enzyme, it has weak anti-ChE activity of its own.

Pralidoxime is injected i.v. slowly in
a dose of 1–2 g (children 20–40
mg/kg). Another regimen is 30
mg/kg i.v. loading dose, followed by
8–10 mg/kg/hour continuous
infusion till recovery.
DOSE
Doses may be
repeated according
to need (max. 12 g
in first 24 hrs.
Lower doses
according to
symptoms are
continued 1–2
weeks).
Treatment should be started as early as possible
(within few hours), before the phosphorylated
enzyme has undergone ‘aging’ and become
resistant to hydrolysis
The use of oximes
in
organophosphate
poisoning is
secondary to that
of atropine.
Treatment should be started as early as possible
(within few hours), before the phosphorylated
enzyme has undergone ‘aging’ and become
resistant to hydrolysis

Other Oximes:
1. Obidoxime: More
potent
2. Diacetyl-monoxime
(DAM): Lipophilic

Parasympathomimetics or Cholinergic Drugs By Baasir Umair

Parasympathomimetics or Cholinergic Drugs By Baasir Umair

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