5 Paracetamol Flashcards

1
Q

maximum total daily dose of oral paracetamol

A

500-mg paracetamol:
3000 mg/day

325-mg paracetamol:
3900 mg

children:
max of 75 mg/kg/day
[or five doses of 10-15 mkdose in a 24-hour period)

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2
Q

peak serum concentrations of oral paracetamol, when?

A

therapeutic doses:
30 mins to 2 hours

overdose:
within 2 hours

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3
Q

recommended dosing of IV paracetamol

A

> 50 kg:
650 mg every 4 hours, or
1000 mg every 6 hours
max total daily dose of 4 grams

<50 kg:
12.5 mg/kg every 4 hours, or
15mg/kg every 6 hours
max individual dose of 750 mg
max total daily dose of 75 mg/kg, or 3750 mg, whichever is less

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4
Q

peak concentration of IV paracetamol

A

occur at the end of the 15-min infusion period

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5
Q

pathophysiology of acetaminophen toxicity

A
  1. normally, acetaminophen is oxidized by the CYP450 system to NAPQI (N-Acetyl-P-benzoQuinone Imine), which is then detoxified by hepatic glutathione to a nontoxic compound that can be renally eliminated (APAP mercaptate?)
  2. however, when glutathione decrease to <30% of normal in the setting of overdose, NAPQI binds to hepatic macromolecules, resulting in CENTRILOBULAR HEPATIC NECROSIS
  3. hepatocyte damage progresses with cell lysis on the SECOND DAY, releasing transaminases and NAPQI-hepatic protein adducts in to the circulation where they are detected in the serum
    -this corresponds generally to the development of OVERT CLINICAL TOXICITY
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6
Q

Stage 1 of acetaminophen toxicity

A

first 24 hours
may be asymptomatic or have nonspicific symptoms, such as anorexia, N/V, malaise

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7
Q

Stage 2 of acetaminophen toxicity

A

days 2-3
findings often improve
but clinical signs of hepatotoxicity - RUQ pain and tenderness- may occur
serum transaminases may be elevated

even without treatment, most patients with mild to moderate hepatotoxicity recover without sequelae

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8
Q

Stage 3 of acetaminophen toxicity

A

days 3 to 4
some patients will progress to fulminant hepatic feilure
Abdominal symptoms
Encephalopathy
Coagulopathy
Renal failure
Metabolic acidosis

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9
Q

stage 4 of acetaminophen toxicity

A

patients who survive the complications of fulminant hepatic failure begin to recover over the next 2 weeks (stage 4)

with complete resolution of hepatic dysfunction after 1-3 months

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10
Q

this may cause early-onset metabolic acidosis

A

ingestion of acetaminophen >500 mg/kg, or peak plasma conc’n >750 mcg/mL (or >5000 mmol/L)

with elevated lactate and altered sensorium

likely mechanism include
-depletion of liver glutathione stores
-resulting in generation of 5-oxoproline
-and metabolit-induced inhibition of mitochondrial respiration

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11
Q

toxic exposure of acetaminophen

A

1) >10 g or 200 mg/kg as a single ingestion or over a 24 hour period

2) >6 g or 150mg/kg per 24 hour period over at least 2 consecutive days

children <6 y/o

1) ≥200 mg/kg as a single ingestion or over an 8 hour period

2) 150 mg/kg per 24 hour period for the preceding 48 hours

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12
Q

graph for acetaminophen toxicity

A

Rumack-Matthew nomogram
toxicity line:
150 mcg/mL
1000 mmol/L
window: bet 4 and 24 hours after ingestion

previously:
>200 mcg/mL
>1300 mmol/L
-60% risk of developing hepatotoxicity (ALT >1000 IU/ML
-1% risk of renal failure
-5% risk of mortality

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13
Q

this has a 90% risk of developing hepatotoxicity

A

> 300 mcg/mL
2000 mmol/L

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14
Q

“toxicity line” for IV acetaminophen

A

any single IV acetaminophen dose abve 60 mg/kg
or acetamoinophen conc’n >50 mcg/mL at 4 hours

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15
Q

MOA of acetylcysteine

A

early acetaminophen poisoning (<8 hours after ingestino)
-acetylcysteine prevents the binding of NAPQI to hepatic macromolecules by acting as a glutathione precursor or substitute, or a sulfate precursor, or
-it may directly reduce NAPQI back to acetaminophen

in established acetaminophen toxicity, or >24 hours after ingestion
-it diminishes hepatic necrosis by acting as an to oxidant
»decreasing neutrophil infiltration
» improving microcirculatory blood flow, or
» increasing tissue O2 delivery and extration

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16
Q

remarks on acetylcysteine

A

If acetylcysteine is given within 8 hours of acetaminophen ingestion, it is nearly 100% effective in preventing the development of hepatotoxicity

17
Q

adverse effect of acetylcysteine

A

anaphylactoid reactions in 4-17% or patients
most during the first 2 hours

mild cases are treated with diphenhydramine

severe cases are treated by temporarily slowing or stopping the infusion

18
Q

regimen of IV acetylcysteine

A

21 hour protocol:

phase I:
loading dose of 150 mg/kg over 1 hour

phase II:
50 mg /kg over 4 hours

phase III:
100 mg/kg over 16 hours

IV acetylcysteine is commercially available as a 20% solution and requires dilution to a 2% solution for infusion into a peripheral vein
both 5% D5W and half-normal saline can be used as diluents

19
Q

oral acetylcysteine regimen

A

72-hour oral acetylcysteine protocol:

140 mg/kg loading dose, then

maintenance doses of 70 mg/kg every 4 hours for 17 additional doses

The taste is disagreeable, may cause N/V, so u may give:
Ondansetron 4-8 mg IV/PO every 8 hours
a/e: QT prolongation

20
Q

Indication of ECMO in paracetamol toxicity

A

“ExtraCorporeal Membrane Oxygenation”

in addition to acetylcystine

ONLY in the setting of encephalopathy,
metabolic acidosis,
elevated lactate, AND
acetaminophen level >900 mg/L

21
Q

when can acetylcysteine be discontinued?

A

if the serum acetaminophen concentration is
<10 mcg/mL
<66 mmol/L

22
Q

remarks on fulminant hepatic failure

A

most fatalities occur on days 3 to 5
those who survive generally begin to show evidence of recovery by days 5 to 7
survivors will eventually develop complete hepatic regeneration without any persistence of hepatic impairment

23
Q

criteria for highest risk of mortality from acetaminophen-induced fulminant hepatic failure

A

King’s College Criteria
metabolic acidosis (arterial pH <7.30) despite fluid and hemodynamic resuscitation

or a cominabtion of
coagulopathy (PT >100s),
renal insuf (crea >3.3 mg/dL, >292 mcmol/L), and
grade III/IV hepatic enceph

24
Q

treatment of fulminant hepatic failure

A

IV acetylcysteine therapy should be continued past the 21-hour standard regiment [at 6.25 mg/kg/hour] until
-the patient recovers,
-receives a liver transplant,
-or dies

25
Q

massive acetaminophen overdose

A

> 40 grams or 500mg/kg

options:
-addition of oral acetylcysteine
-increasing the phase III to 200 mg/kg over 16 hours from 100 mg/kg over 16h
-or reloading the standard acetylcysteine regimen at completion of the 21-hour protocol