Treatment of Pain Flashcards
Pain is difficult to catch up with; (…) are more effective when given (…) pain increases
- analgesics
- before
What is the chemical name for acetaminophen and the abbreviation?
- N-acetyl-para-aminophenol
- APAP
What is the mechanism of action of acetaminophen?
- not full understood
- possibly blocks central (not peripheral) prostaglandin production
What are the uses of acetaminophen?
- antipyretic
- analgesic
What are the different formulations of acetaminophen?
- oral: capsule, tablet (chewable and ER), elixir, gel, liquid, solution, suspension, syrup, sachet (tear open and put into water)
- rectal suppository
- IV
What are the advantages to using acetaminophen vs other pain medications?
- no GI irritation
- almost no allergy
- no bleeding issues
- very safe at usual doses (TI approx. 10)
- safe in pregnancy
What are the disadvantages of using acetaminophen vs other pain medications?
- poor anti-inflammatory action (treats pain/reduces fever but no inflammation)
What are the side effects associated with acetaminophen use?
- methemoglobinemia, leukopenia rare (hemoglobin abnormal; cyanosis in babies)
- liver toxicity due to metabolite accumulation (more concerned about)
What is the 2nd most common cause of liver disease that requires transplant?
liver toxicity due to acetaminophen use
What are the different metabolite forms of acetaminophen?
- sulfate form
- glucuronide form
- N-acetyl-p-benzoquinone imine (NAPQI)
What is acetaminophen normally metabolized by?
glucuronidation and sulfation with minor CYP2E1
In acetaminophen, (…) is overwhelmed and metabolism shifts to (…), producing the toxic metabolite (…)
- phase II
- phase I
- NAPQI
Describe the steps of normal acetaminophen metabolism and what happens when an overdose of acetaminophen occurs.
- acetaminophen is mainly metabolized through glucuronidation and sulfation (phase II) with a little being metabolized by CYP2E1 (oxidation/CYP450)
- when overdose occurs, there isn’t enough molecules for glucuronidation and sulfation to occur so more acetaminophen goes through CYP2E1 (phaseI) to be converted to NAPQI, which is toxic
- usually the small amt of NAPQI is detoxified/eliminated by glutathione conjugation, but there is only a certain amount of this to allow it to occur
- so in overdose, glutathione conjugation is overwhelmed from the large amount of NAPQI and NAPQI remains in the system to interact with cellular macromolecules and cause toxicity
Toxic chronic doses of acetaminophen can occur when taken over time in a period longer than (…)
4 hours
A normal dose of acetaminophen is (…) in patients with liver impairment
toxic
What are risk factors for toxicity with acetaminophen? Explain each.
- malnutrition (decreased glutathione)
- chronic alcohol ingestion (induces 2E1)
- concomitant use of drugs that are CYP2E1 inducers
- young, febrile children (usually less serious, not intentional OD so severity will be less)
- Describe adult acetaminophen OD?
- Describe child acetaminophen OD?
- more severe, more fatal
- more frequent, less severe
Anything that induces (…) will facilitate acetaminophen to be converted to (…) causing toxicity
- 2E1
- NAPQI
What are the different phases of acetaminophen toxicity?
- phase 1: up to 24 hours after intake
- phase 2: 18-72 hours later
- phase 3: 72-96 hours later
- phase 4: 4 days to 3 weeks later
What are the symptoms associated with each phase of acetaminophen toxicity?
- phase 1: GI upset or no symptoms at all
- phase 2: RUQ pain +/- tenderness (liver); continued or new onset of GI issues
- phase 3: all of the above continue; hepatic dysfunction begins
- phase 4: resolution of symptoms and organ failure, if patient survives; complete resolution of hepatic damage may take months
What is associated with hepatic dysfunction (acetaminophen toxicity)?
- coagulopathy
- jaundice/encephalopathy
- hypoglycemia (failing liver doesn’t product a lot of sugar)
What are ways you can treat acetaminophen toxicity?
- activated charcoal (if ingestion occurred w/in an hour and patient is stable)
- n-acetylcysteine/NAC (acetadote) - always use in overdose situations w/ acetaminophen
- How does n-acetylcysteine work in acetaminophen toxicity?
- What are the regimens for it?
- Which may be more effective in what time frames?
- provides cysteine group for glutathione synthesis (so NAPQI can be detoxified/eliminated)
regimens: - 72-hour oral or 21-hour IV
- oral mixed w/soda or juice and chilled
effectiveness: - oral may be more effective for pts presenting > 18 hours after ingestion
- IV is more effective for pts presenting within 12 hours
What is the revised Rumack-Matthew Nomogram for the Acute Ingestion of Acetaminophen? (what it is used for)
- used to interpret serum concentrations of acetaminophen in relation to time since ingestion measured from ingestion of first dose, in order to assess potential hepatotoxicity
- acute = under 24 hours
- NAC administration to any patient with a blood level above the treatment line
- above treatment line: treat them; below treatment line: don’t treat them