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MBBS IV - Supplementary Courses > Chemical Pathology IV - Poison and Drug Abuse > Flashcards

Chemical Pathology IV - Poison and Drug Abuse Flashcards

1
Q

Toxic dose of paracetamol

Linked with what type of abnormal behavior

A

> 7.5g
150mg/kg

Deliberate Self-harm or suicidal behavior

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2
Q

Paracetamol metabolism

A

Paracetamol metabolism: Excreted in urine

1) 5% unchanged
2) UDP- glucuronosyl transferase&raquo_space; Paracetamol glucuronide
3) UDP-sulfate transferase&raquo_space; Paracetamol sulphate

4) CYP&raquo_space; NAPQI** (cellular toxicity)&raquo_space; conjugated with glutathione&raquo_space; Glutathione cysteine mercapturic acid (non-toxic)

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3
Q

Which intermediate metabolite of paracetamol cause cellular toxicity?
What organs affected?

A

NAPQI
N-acetyl-p=benozequinone imine

Bind to cellular proteins and cause hepatic and renal toxicity
Liver failure + GI symptoms + Kidney injury

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4
Q

Metabolism of paracetamol in overdose?

A

UDP conjugation and direct excretion is stopped

All paracetamol goes through CYP metabolism to NAPQI

NAPQI not conjugated fast enough into non-toxic Glutathione Cysteine mercapturic acid

Accumulation of NAPQI

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5
Q

Which pathways in paracetamol metabolism can be induced by N-acetylecysteine?

A

1) NAPQI&raquo_space; conjugation with glutathione&raquo_space; Glutathione Cysteine mercapturic acid
2) Paracetamol&raquo_space; UDP-sulfate transferase&raquo_space; Paracetamol sulphate

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6
Q

Acute presentation of paracetamol overdose?

A

GI symptoms in 24 hours

Liver failure and kidney injury in 2-3 days

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7
Q

Name of graph used to Dx paracetamol toxicity.

Plasma concentration is measurable after how many hours?

A

Rumack- matthew normogram

Negatively correlated (non-linear)
Decrease in plasma concentration with time

150ug/mL at 4 hours post-ingestion
Half life taken every 4 hours

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8
Q

How to use paracetamol plasma concentration to determine treatment or not?

A

Refer to the hours post-ingestion
If concentration is above the broken line on reference graph (Rumack-matthew normogram) = Potential for toxicity = treat immediately

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9
Q

Treatment options for paracetamol poisoning

A

1) N-acetylcysteine: for late presentation, high parenchymal enzyme, massive dose
2) Gastrointestinal decontamination with Activated charcoal

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10
Q

Limitations to Runmack-matthew normogram for Dx of paracetamol toxicity (3)

A

Problems with

  • Extended release pills
  • Staggered overdose
  • Serum level unpredictable before 4 hours post-ingestion
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11
Q

Pathophysiological mechanism of Carbon monoxide? (3)

A
  • High affinity to Hb, Decrease O2 delivery
  • Impair cytochrome oxidase and O2 use in cells
  • Lipid peroxidation in CNS: Globus pallidus lesions
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12
Q

What determine elimination half life of Carbon monoxide?

A

FiO2

FiO2: Percentage of oxygen in the air mixture that is delivered to the patient.

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13
Q

What is Methemoglobin

A

Continuous production and reduction in vivo

Methemoglobin = a form of hemoglobin that has been oxidized, changing heme iron configuration from the ferrous (Fe2+) to the ferric (Fe3+) state.

methemoglobin does not bind oxygen and cannot deliver oxygen to the tissues.

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14
Q

Causes of high methemoglobin

A

Congenital

  • CYB5A/ C6B5R deficiency (enzymes that convert Fe3+ to Fe2+ for oxygen carrying)
  • HbM (conformational change in Hb, cannot carry O2l)

Acquired:

  • Medicine
  • Chemicals
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15
Q

List some acquired causes of methemoglobin

no need to remember exhaustively

A

Medication:

  • Chloroquine
  • Phenazopyridine
  • Local anesthetics

Chemicals:

  • Antifreeze
  • Hydrogen peroxide (disinfectant)
  • Nitrates and nitrite
  • Napthalene (moth balls)
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16
Q

Treatment of carbon monoxide poisoning?

A

High FiO2: hyperbaric oxygen therapy

Stop acquired causes of methemoglobin production (e.g. stop exposure to hydrogen peroxide)

17
Q

Sources of cyanide poisoning

A
  • Fire, burn victim
  • Nitroprusside (Malignant hypertension treatment)
  • Cyanide, Hydrogen cyanide, Cyanogen, Nitriles, Cyanogenic glycosides
18
Q

Biochemical markers for cyanide poisoning?
Acid/ base balance?
pO2?

A

3 markers:

  • Thiocyanate (long half-life)
  • Cyanide
  • ATCA (Stable minor metabolite)

High anion gap metabolic acidosis due to lactate (Lactate >8mmol/L)
Decreased A-V pO2 gradient

19
Q

Antidotes to Cyanide? (2)

A

Sodium nitrite

Hydroxocobalamin

20
Q

Pathophysiological mechanism of cyanide poisoning?

A

Inhibits cytochrome oxidase

> > Stop electron transport chain&raquo_space; Cannot crate hydrogen ion gradient&raquo_space; Cannot make ATP

21
Q

Testing for cyanide poisoning?

A

Spot tests and definitive tests:

  • Colorimetric dipstick reaction (Koenig reaction, turn purple)
  • Test metabolites: Thiocyanate, ATCA, Cyanide
22
Q

2 sources of methanol poisoning?

Pathophysiological mechanism?

A

Fake wine, Industrial solvent

Cytochrome oxidase inhibitor, similar to cyanide poisoning&raquo_space; Lactic acidosis from tissue hypoxia

23
Q

Test for methanol poisoning?

A

Potassium permanganate + Sodium bisulfite + chromotropic acid&raquo_space; Purple colored compound

24
Q

How to use anion gap and osmolar gap to tell the time of methanol poisoning?

A

Methanol&raquo_space; formaldehyde&raquo_space; formate&raquo_space; metabolic acidosis

Initial:
High Osmolar gap due to methanol (presence of osmotically active solutes)

Late:
High Anion gap as most methanol is turned into Formate

25
Q

2 treatment for methanol poisoning

A

Ethanol

Fomepizole - Alcohol dehydrogenase inhibitor

26
Q

Acid/base balance after salicylate poisoning?
Define level for salicylate poisoning?
What to test for salicylate poisoning?

A 
Metabolic acidosis (lactate) + respiratory alkalosis 
Toxic: >= 2.2mmol/L

Test blood salicylate levels - check conversion of methylsalycylate to salicylate by liver

27
Q

Testing for Salicylate poisoning?

A

Take blood:

- Liquid chromatography + Time of flight mass spectrometry

28
Q

2 reasons why urine toxicology not useful in overdose management? (check)

A
  • Always a retrospective test: Not real-time diagnosis

- Incidental findings are not helpful in real-time management

29
Q

Use of urine toxicology screening?

A

Point of care tests (at A&E)

30
Q

Test for drug abuse?

A

Immunoassays: general unknown screening (find class of drug) + target analysis of drug abuse (find exact drug)

  • Opiates: methadone, fentanyl…
  • Methamphetamine/ Amphetamine
  • Benzodiazepine
  • Cocaine
  • Cannabis
31
Q

5 functional classes of abused drugs?

A
  • Stimulants
  • Depressants
  • Dissociative
  • Psychedelics/ Hallucinogen
  • Cannabinoids
32
Q

MoA of CNS stimulants

5 Examples of stimulants

A

Increase dopaminergic or serotoninergic activity
- Arousal, hyperactivity…etc

Cocaine 
Amphetamine 
MDMA 
Ritalin 
Caffeine
33
Q

MoA of CNS depressants
Overdose effect?
3 examples?

A

Depress CNS activity: anxiety suppression, sedation, pain relief

Overdose = coma

Examples:

  • Opioids, benzodiazepines
  • Z-drugs (Zopiclone, Zolpidem)
  • GABAnergic drugs
34
Q

MoA of CNS dissociatives
Overdose effect?
3 examples?

A

Distort sensory perception, detachment from environment and self

Overdose: General anesthesia, respiratory suppression, seizures, K-hole

Ketamine, Phencyclidine (PCP_

35
Q

MoA of CNS pyschedelics

3 examples?

A

Change mood and perception, increase serotoninergic activity, Hallucination

LSD
Tryptamines
Psilocybin mushrooms

36
Q

MoA of cannabinoids

Types

A

Activate CB1 and CB2 receptors

THC - tetrahydrocannabinol
CBD - Cannabidiol

37
Q

4 examples of TCM poisoning

A

Toxic plant alkaloids: Aconitum, Solanaceous…

Cardiac glycosides

Gelsemium alkaloids

Heavy metals

38
Q

What to do if plasma paracetamol concentration persists and does not go below dotted line on Runmack-matthew normogram?

A

Suspect sustained release formula

Give N-acetylcysteine

39
Q

Lactate caused metabolic acidosis + High initial osmotic gap + Late high anion gap?

A

Methanol poisoning

MBBS IV - Supplementary Courses (54 decks)

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