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Flashcards in topic 22 Deck (29):
1

What are 4 forms of toxic RXNS?

• Local (irritant) effects

• Systemic effects

• Combination of both

• Affect substrate delivery or utilization

– Oxygen

– Glucose

• Free radical formation (toxic intermediary)

• Toxic metabolite formation (e.g., formic acid from methanol)

• Enzymatic deficiency revealed (G6PD)

• Affect metalloproteins

• Allergic reactions

• Hypersensitivity reactions

2

What is an antidote that can be used for a variety of toxicants such as CO? How is it used?

• Oxygen is an essential

“antidote” used for the

treatment of a variety of

toxicant exposures (e.g.

carbon monoxide).

• Oxygen usually applied

via high flow face mask

10-15 L/min.

3

What are some toxicants tha twill cause hypoglycemia? What are the effects? What is the antidote? How is it applied?

• Hypoglycemia is possible from several drugs

and toxicants such as insulin and oral

hypoglycemic agents (sulfonylureas) as well

as beta-blockers, alcohol, quinine and

salicylates.

• Inadequate cellular energy for normal

function, most acutely noticeable as impaired

brain function.

• Concentrated dextrose solution ( D50%,

D25%, D10%) treats hypoglycemia.

4

What is an example of a toxicant that effects transport of oxygen? How does it do so? What are the results?

• Carbon monoxide binds to hemoglobin with

much higher affinity than oxygen.

• This leads to a functional defect in forming

oxyhemoglobin and thus leads to decreased

oxygen delivery to the body.

• Hemoglobin cannot bind oxygen.

• Carbon monoxide also affects the cytochrome

oxidases, which contributes to lower energy

production by cells. The overall effect is

tissue hypoxia.

5

What are 2 examples of toxicants that effect the transport of oxygen?

CO, Methemoglobin formers

6

How do methemoglobin formers work?

• Methemoglobin is another example of a toxic effect on hemoglobin as a metalloprotein.

• Methemoglobin is hemoglobin in the oxidized ferric state (Fe3+) and cannot carry oxygen for cellular delivery.

• Normally, the iron or “heme” in hemoglobin is in the Fe2+ state which is capable of “picking up” oxygen to transport.

7

What is an example of a toxicant that releases free radicals or toxic electrophiles? How is it metabolized? What is the result of too much of it? How is it normally detoxified?

APAP (Acetaminophen)

• Electrophiles “love to attack” molecules with
abundant outer shell electrons.

• Metabolism of acetaminophen (APAP or acetyl-para-amino-phenol) occurs via glucuronidation, sulfation and hepatic cytochromes (mainly CYP 2E1).

• Overdose of APAP may result in excessive amounts of the reactive electrophile NAPQI

• Normally, any small amount of this reactive metabolite once formed is detoxified by endogenous (i.e., made in the body) glutathione.

• Its sulfhydryl group will bind many toxic
compounds including NAPQI.

8

What does G6PD do? Why is it necessary? What happens if its deficient?

• G-6-PD catalyzes the conversion of glucose-6-phosphate to phosphonolactone and thereby reducing NADP+ to NADPH.

• NADPH is required for glutathione production,
which is a natural antioxidant.

• If the patient with G-6-PD deficiency is exposed to
strong oxidant drugs (eg. sulfacetamide, dapsone) or chemicals (naphthalene, methylene blue) the sulfhydryl groups on RBC membranes are more susceptible to attack by reactive oxygen species.

• Hgb is damaged and precipitates as Heinz bodies – RBC membranes are deformed and cells hemolyze

9

What are two examples of toxicants that are metabolized to toxic products? What are the products? How is this treated?

• Methanol or ethylene glycol are metabolized to toxic products such as formic acid or glycolic acid by hepatic alcohol dehydrogenase (ADH).

• The key to toxicologic management is prevention of formation of these toxic metabolites.

• Competitive inhibition of ADH by ethanol is usually effective, but is largely replaced by a specific ADH inhibitor, 4-methylpyrazole, also known as, fomepizole (Antizol®).

10

What are some general principles to the organ system approach? What are the two most common history taking mistakes?

• First “Treat the Patient, not the Poison”
• A,B,C’s: Airway, Breathing, Circulation
• Obtain relevant history of exposure (type,
amount, duration, etc)
• Remember, the two most common mistakes that
can occur while obtaining history from patients
are when you:

• listen to the patient and believe everything

• don’t listen to everything the patient says

11

What are some side effects of isoniazid? How does it do this? What is the antidote?

Seizures, Metabolic acidosis

• INH also inhibits lactate dehydrogenase that converts lactate to pyruvate and thus lactic acidosis may develop
• INH poisoning will result in seizures.
• Lactic acid may also build up from the excessive muscular activity from seizures.


• Etiology of INH-induced seizures involves a
decrease in the availability of gamma-
aminobutyric acid (GABA).
• Isoniazid metabolites bind to pyridoxine and
inactivate it.
• Isoniazid and hydrazines also inhibit the
enzyme pyridoxine phosphokinase and thereby decreases conversion of pyridoxine (Vit B6) to active pyridoxal-5-phosphate.
• Because pyridoxal phosphate is an essential cofactor for glutamic acid decarboxylase, which converts glutamate to the inhibitory neurotransmitter GABA, any disruption of this metabolic pathway may result in decreased GABA, and consequently, increased chance of seizures.

Pyridoxine (Vit. B6) is the antidote...a benzo alone probably won't get rid of the seizures

12

What neurological aspects of the body can be affected by toxins? How?

• Pharmaceuticals and toxins may affect:
– Central Nervous System

– Peripheral Nervous System
• Over 90% of all toxic effects on peripheral nerves are axonopathies (may be a board ?)
• Neuronopathies
• Myelinopathies

– Mixed CNS & PNS

13

How might CNS toxin effects manifest?

• CNS toxin effects may manifest as:

– Change in LOC or confusion
– Coma
– Seizures
• Many causes (see Goldfrank’s table)

14

What are some toxic causes of seizures? What is the most common cause?

– Cyclic antidepressant overdoses are certainly common causes for seizures

– Small children can also access camphor from
Camphophenique® and similar products and this can cause seizures

• But the most common cause of seizures from
toxins is actually withdrawal from alcohol.

• Cocaine-induced seizures are also common.

• Amphetamines including MDMA can cause seizures

• But isoniazid (INH) is a big one to remember especially with TB resurgence (also with INH remember pyridoxine or Vitamin B6 is antidote)

• Overdoses of many anticonvulsants may result in seizures.

15

What are some mechanisms by which toxins can cause seizures?

• Seizures from toxins can be caused by a variety of mechanisms:
– Sodium channel poisoning

– GABA-chloride channel poisoning

– NMDA receptor stimulation

– Metabolic causes
• Hyponatremia
• Hypoglycemia
• Hypocalcemia
• Hypomagnesemia
• Hypophosphatemia

16

How are toxin induced seizures treated?

• A,B,C’s

• Thiamine and glucose for alcoholics

• Check glucose, sodium, calcium or magnesium depending upon situation and treat as necessary.

• Benzodiazepines (e.g. lorazepam) are generally the drugs of choice for toxic exposures

17

What are benzodiazepines used for? What are two examples? What is the second line treatment for toxic caused seizures? Which drug should not be used for it?

• Diazepam (Valium®) & Lorazepam (Ativan®)

• For urgent treatment of ANY hyper-stimulated CNS state
– seizures of unknown origin (hypoglycemia is generally ruled out first)
– agitation from various causes such as drug toxicity
or withdrawal,
– decompensated psychiatric illness.

• Little risk to pushing the dose as high as necessary to control the condition but bewareof respiratory depression.

• Can use phenobarbital as second line (consider propofol) but support airway as needed

• Avoid phenytoin or fosphenytoin (one reason is that there is no co-receptor for this anticonvulsant on the GABAA channel complex like there is for benzodiazepines or phenobarbital).

18

What are two ways in which the ANS can be affected by toxins?

Acetylcholine excess can affect the parasympathetic & sympathetic system
– Muscarinic effects
– Nicotinic effects

Acetylcholine release blockade

19

What is one example of a toxin that stimulates release of ACh? 3 examples that inhibit it?

• Acetylcholine release enhanced by: – Black Widow Spider (beta-latrotoxin)

• Acetylcholine release inhibited by:
– Crotalidae venoms

– Elapidae venoms (beta-neurotoxins)

– Botulinum toxin

20

What are the clinical manifestations of botulinum toxin? How does it work?

• Botulinin toxin inhibits Ach release.

• Clinical manifestations of decreased Ach release include

– ptosis (eyelid droop)
– weakness
– cranial nerve palsies
– respiratory failure

• Acetylcholine stored in vesicles is unable to

be released because several of the serotype

toxins cleave various proteins responsible for

vesicle attachment to the membrane and

neurotransmitter release

21

What are five ways in which toxins can affects NTs and ion channels in the CNS?

• Key ion channels and G proteins

– Sodium, potassium, calcium ionophores

• Na+/K+-ATPase pump

• GABAA Cl-

• Biogenic amines (NE, Epi, DA)

• Serotonin (5-HT)

channel

22

What are some key ion channels? Why are they important?

• Ion channels are not only important in
toxicology with respect to neurons but also
cardiac cells (Action potential)
– Sodium (Na+) channel
– Potassium (K+) channel
– Calcium (Ca++) channel

23

What channels are opened and closed during an action potential?

• Resting state
–Negatively charged cell interior
–Resting membrane potential (“charge”): - 70mV

• Excited state
– Caused by rapid sodium (Na+) influx
• Sodium channels open suddenly & simultaneously at threshold, i.e., the firing level, - 55 mV
• Generates action potential (“charge”)
– + 35 mV
– Positively charged cell interior
• Transmits electrical signal along the neuron

• Chloride (Cl-) influx
– Chloride enters nerve cell via GABAA/drug
receptor-chloride channel complex
– Makes cell interior more negative
• Further from threshold
• Less likely to fire
– Calming
– Sedating
– Antiepileptic (prevents seizures)

24

What causes NE release? What inhibits NE reuptake? What stimulates NE binding via NE transporter inhibition?

• NE release (eg amphetamines, cocaine)

• NE reuptake inhibition (eg CADs)

• NE binding via NE transporter inhibition

(eg CBZ, cocaine, CADs)

25

What can cause excessive dopamine activity? What can dopamine antagonism? What are the reults of each?

• Dopamine agonism or antagonism accounts for a
number of toxicologic emergencies.

• Excessive DA activity may be seen after overdoses of amphetamines, methylphenidate or even over-the-counter decongestants (pseudoephedrine) resulting in dystonia, choreoathetosis and other movement disorders.

• DA antagonism as seen with overdoses or therapeutic uses of butyrophenones such as haloperidol (e.g., Haldol®) or phenothiazines may also result in Neuroleptic Malignant Syndrome (NMS).

26

What causes NMS? What are its clinical manifestations?

• Neuroleptic Malignant Syndrome (NMS) involves
disequilibrium in DA and manifests with:
– Hyperthermia (elevated body temperature),
– Altered mental status,
– Autonomic dysfunction, and
– Muscular hypertonicity

27

What are 5 major diagnostic criterion for NMS? What is one minor criterion?

• Recent use of an antipsychotic drug (e.g. ziprasidone, haloperidol, fluphenazine) or other dopamine altering drug is an essential criterion;

• Fever (>38° C or 100.4° F) without other cause is a major criterion;

• Muscle rigidity is a major criterion;

• Elevated CK (CPK) > 1000 U or 3 x normal CK (creatinine phosphokinase, normally found in muscle fibers; released into the bloodstream when muscles undergo damage/breakdown) is a major criterion

• Autonomic instability (2 or more of sweating, tachycardia, elevated or decreased blood pressure) is a major criterion.

• Leukocytosis (elevated white blood cell
count > 12,000) is a minor criterion

28

What are some symptoms of serotonin toxicity?

• Confusion or disorientation, agitation, and coma are the top three reported signs and symptoms within the cognitive/behavioral category.

• Diaphoresis (excessive sweating), hyperthermia,
sinus tachycardia, hypertension and tachypnea (fast breathing) are common manifestations of autonomic dysfunction.

• Myoclonus, hyperreflexia, muscle rigidity and tremors are the four most common neuromuscular abnormalities reported.

29

What are 4 examples of drug combinations that are associated with serotonin toxicity?

• Several drugs and drug combinations have been
associated with Serotonin Toxicity :
– SSRI (e.g. fluoxetine) + MAOI
– SSRI + meperidine
– SSRI + CAD/TCA (tricyclic antidepressant)
– SSRI/SNRI (e.g. venlafaxine)