Pain: Pharm - Acetaminophen Flashcards
Pain
Pharmacological Management of Pain
Non‐prescription options: (3)
- Non‐opioids
◦ Acetaminophen
◦ NSAIDs - Counter irritants and topical products
- Muscle relaxants
Pain
Pharmacological Management of Pain
According to World Health Organization Analgesic Ladder, what is the recommendation for treating MILD pain?
Non-opioid: Acetaminophen (paracetamol) Aspirin, NSAID \+- adjuvant (drug or other substance, or a combination of substances, that is used to increase the efficacy or potency of certain drugs)
Pain
Pharmacological Management of Pain
According to World Health Organization Analgesic Ladder, what is the recommendation for treating MILD to MODERATE pain?
Opioid:
Codeine, Tramadol, etc.
+- non-opioid
+- adjuvant
Pain
Pharmacological Management of Pain
According to World Health Organization Analgesic Ladder, what is the recommendation for treating MODERATE to SEVERE pain?
Opioid:
Morphine, Fentanyl, etc.
+- non-opioid
+- adjuvant
Pain - Acetaminophen
What is it used for?
Analgesic, antipyretic
Used for mild – moderate pain (≤ 4‐6/10)
Pain - Acetaminophen
What is its MOA?
MOA:
inhibits prostaglandin synthesis in CNS (?COX‐3),
inhibits heat regulation in hypothalamus
Pain - Acetaminophen
Can also found in what other medications?
Also found in combination with OTC products & opioids (e.g. codeine, oxycodone)
◦ e.g. Tylenol No. 1 (OTC) or Percocet 352/5mg (Rx)
Pain - Acetaminophen
Adult Dosage forms?
◦ PO Immediate release 325mg, 500 mg (available in
tabs, caps, etc.)
◦ PO Extended release 650mg (i.e., Tylenol Arthritis®)
◦ PR 325 & 650mg (Why would we select this dosage
form?)
Pain - Acetaminophen
Pediatric Dosage forms?
◦ PO liquid 80mg/ml & 160mg/5ml (Why might we
select one concentration over the other?)
◦ PO chew tabs 160mg
Pain - Acetaminophen
Plasma levels peak ____ h post ingestion, t1⁄2 2 hours
1‐2 h
Pain - Acetaminophen
Metabolized in the _____ & excreted by
liver
kidney
Pain - Acetaminophen
Acetaminophen Dosing
Adult Dosing?
◦ Max 4 g/day; in the elderly, often max at 3.2 g
◦ 325–500 mg Q3H PRN PO or 325–650 mg Q4H PRN
PO or 650–1000 mg Q6H PRN PO
◦ (extended) 1300 mg po q8h
◦ Maximum dose: 4 g/day from all sources
Pain - Acetaminophen
Acetaminophen Dosing
Renal dysfunction?
◦ CrCl< 50 ml/min – q6h
◦ CrCl<10ml/min – q8h
Pain - Acetaminophen
Acetaminophen Dosing
Hepatic dysfunction – caution?
◦ low dose usually well tolerated(< 2.6 g / day)
Pain - Acetaminophen
Acetaminophen Dosing
Children?
◦ 10‐15 mg/kg po q4‐6h (max 5 doses/day)
◦ Fixed dosing (weight preferred to patient age)
Pain - Acetaminophen
What cause Acetaminophen Adverse Effects?
acute hepatotoxicity with acute overdose or chronic ingestion of high doses
Pain - Acetaminophen
What are some Acetaminophen Adverse Effects findings?
◦ In Canada, more than 4,000 hospitalizations each
year (2014)
◦ Most common drug overdose (1/5 cases due to
unintentional dosing)
◦ Common in adolescents and young adults
◦ 1/5 cases occur even after dosing within
recommended guidelines, but this may be due to risk
factors such as alcoholism or liver disease
Pain - Acetaminophen
Toxic levels?
10 g/d or 150 mg/kg/day are known to be toxic
BUT toxicity can occur at doses < 4 g/day
Pain - Acetaminophen
Acetaminophen Adverse Effects Early symptoms? (4)
abdominal pain
fatigue
anorexia
fever
Pain - Acetaminophen
Acetaminophen Adverse Effects Allergy Alerts?
Allergy Alert – has been associated with
SJS
urticaria
angioedema
Pain - Acetaminophen
Acetaminophen Drug – Disease interactions?
◦ increase risk of toxicity with EtOH > 3 drinks/day,
malnutrition, & preexisting hepatic disease
Pain - Acetaminophen
Acetaminophen Drug – Drug interactions?
Few clinically significant drug‐drug interactions
◦ Warfarin & acetaminophen ≥2g/day for >3 days
◦ Anticonvulsants PHT, CBZ may increase risk of
hepatotoxicity
- i.e., phenytoin, carbamazepine
Pain - Acetaminophen
Acute Acetaminophen Toxicity can be impacted by: (5)
the quantity duration co‐ingestion comorbidities timing of medical interventions
Pain - Acetaminophen
Acute Acetaminophen Toxicity level: __ g/day or
___ mg/kg/day
10 g/day or 150 mg/kg/day
Pain - Acetaminophen
How many stages in Acute Acetaminophen Toxicity?
4
Pain - Acetaminophen
Stage 1 in Acute Acetaminophen Toxicity:
Stage 1 – 0.5‐24 h post
◦ May be asymptomatic or generalized symptoms
(nausea, vomiting, malaise, pallor, diaphoresis, and
anorexia)
◦ LFT WNL; usually normal PT
Pain - Acetaminophen
Stage 2 in Acute Acetaminophen Toxicity:
Stage 2 – 24‐48 h post (hepatic injury)
◦ increase AST/ALT, PT/INR? Bili?
◦ RUQ pain, abd tenderness, oliguria (decreased urine
output)
Pain - Acetaminophen
Stage 3 in Acute Acetaminophen Toxicity:
Stage 3 – 72‐96 h post (hepatic failure)
◦ Variable peaks in transaminases
◦ Hepatic necrosis and dysfunction are associated
with jaundice, coagulopathy, hypoglycemia, and
hepatic encephalopathy
Pain - Acetaminophen
Stage 4 in Acute Acetaminophen Toxicity:
Stage 4 ‐ > 4 days to weeks (recovery)
Pain - Acetaminophen
Why avoid Tylenol #1s if possible?
Schedule 2 product
Acetaminophen 300 mg/codeine 8 mg/caffeine 15 mg
Limited evidence for efficacy vs other simple analgesics
◦ Combination products containing acetaminophen,
caffeine and codeine (8 mg) have not demonstrated
benefit in the management of acute or chronic
nonspecific low back pain.
Risk of dependence and diversion
Avoid if possible!
