Intro to pharmacology of analgesic agents - Pharmacology Flashcards

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1
Q

Define pain

A

An unpleasant sensory and emotional experience which we primarily associate with tissue damage or describe in terms of tissue damage or both (IASP definition).

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2
Q

List the sources of pain

A

Injury

Disease

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3
Q

What is the sensory pathway?

A
Transduction
Transmission - sensory fibres  (touch, pain)
Transmission - spinal cord
Perception/learning - limbic
Transmission - thalamus
Perception - somatosensory cortex
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4
Q

How is pain modulated?

A

Emotion and attention profoundly modulate nociception
Amount of pain experience does not relate to severity of tissue damage
Anxiety increases pain transmission

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5
Q

Examples of dental pain?

A

Infec - acute inflam
Exposed nerve endings - neurogenic pain
Swelling in confined space - pressure effects
Fear and anxiety

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6
Q

How to treat pain?

A
Reduce tissue damage;
- Non steroidal anti-inflam drugs
- Steroids
- Cooling
Nerve block - LA
Spinal cord - opioids
CNS - Opioids, psychological factors
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7
Q

What does the world health organisation do?

A
Believe the pt
History of symptoms
Assess severity
Physical exam
Pain management
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8
Q

What are the WHO steps?

A

Step 1 - mild pain
- ‘Non-opioids’

Step 2 - mod pain
- Weak opioids and ‘’

Step 3 - severe pain
- Strong opioids and ‘’

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9
Q

What is the placebo effect?

A

Placebo is anything administered which is
pharmacologically and physiologically inert
• Placebo is not ineffective therapeutically. Can
have a measurable effect
• Reassurance and confidence in one’s therapy
may also have an effect.

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10
Q

Features of paracetamol?

A

Inhibition of the synthesis of prostaglandins
Not much anti-inflam effect
Antipyretic
Analgesic
Oral, soluble potions, intravenous, rectal
1g 4-6 hourly adult does 4g in 24hrs
Adverse effects uncommon
Hepatotocitity if overdose - early treatment with N-acetyl-cysteine

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11
Q

NSAID features?

A

Aspirin, ibuprofen, naproxen, indomethacin
Irreversile inhibitor of cyclooxygenase (COX1 or 2 enzyme)
COX generates inflam mediators: prostaglandins and theromboxanes
COX inhibitions are effective at reducing acute inflam
Adverse effects due to extension of therapeutic effects

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12
Q

Effects of NSAIDS on the body?

A

GIT: Occult GI blood loss from minor breaches in mucosa, peptic ulceration, upset, indigestion

Renal function - reduction in intrarenal blood flow = renal failure

Platelets: COX inhibition, bleeding tendency

Cardiovascular: as a result of altered renal function, fluid retention can precipitate heart failure

Resp: Some aspirin sensitive asthmatics

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13
Q

Features of COX2?

A

Less bleeding as GIT and platelets have mainly COX1
Newer COX2 inhibitors: Parecoxib celecoxib
Not less nephrotic

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14
Q

How are COX2 and cardiovascular disease related?

A

COX2 and CV disease:

  • Absence of antiplatelet effects
  • Slightly pro thrombotic
  • Increased risk MI and stroke

Contraindicated in CV disease

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15
Q

When elective surgery is required, how are NSAIDs involved?

A

Stop NSAIDs consumption at least 5 days before elective surgery
Bleeding at operation: platelet transfusion
Consider platelets if emergency surgery

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16
Q

What opioids should be used for moderate to severe pain?

A

Codeine
Di-hydrocodeine
= Weak opioids
Both metabolised to morphine

17
Q

What effect do opioids have on the CV system, resp and GI tract?

A

CV - reduced sympathetic outflow, increased vagal tone, bradycardia, hypotension, excitation

Resp - inhibit cough reflex, resp depression

GI tract - Reduced gastric motility, constipation, nausea and vomiting

18
Q

CNS opioid effects?

A

Sedation, euphoria, excitation
Analgesia:
- Spinal cord = reduced pain fibre transmission kappa opiod receptors
- Brainstem = reduced pain projection to higher centres - Mu opioid receptors

Resp depression, reduced brainstem response to hypoxia and hypercarbia

19
Q

How to reverse opioid effects?

A

• Naloxone 400 mcg i.v. dramatic reversal of mu receptor opioid effects.
• Far less effective on newer synthetic opioid like
substances as their effects in the CNS are less well
defined

20
Q

What occurs with chronic opioid use?

A

Reduced effect as CNS becomes more tolerant - dose increase

21
Q

When opioid dependency is reached, what occurs with acute withdrawal?

A

Hypertension, tachycardia,

tachypnoea, diarrhoea, sweating, anxiety, hallucinations.

22
Q

What do chronic opioid medications cause?

A

Withdrawal reactions if stopped suddenly

23
Q

Give examples of newer oral opioids, features?

A

Tramadol and nefopam

= as effective as codeine, less variability and constipation

24
Q

List the usual opioid effects?

A

Sedation, dizziness, nausea, occasional flushing/sweating with tramadol

25
Q

Adverse effects of tramadol?

A
Overdose = resp depression
Dependency = difficult to withdraw
New legislation: controlled drug (class 3) = prescription only and must be signed for
26
Q

Give examples of weak opioids

A

Co-codamol, co-proxamol

27
Q

Group cautions when prescribing opioids?

A

Dependent on hepatic metabolism and renal
excretion of metabolites. Some active metabolites

Prolonged effect in liver or renal impairment
Respiratory disease, sleep apnoea, increased
sensitivity
Aim for minimum duration of prescription

28
Q

What do WHO suggest to use with severe pain?

A

Morphine, diamorphine, fentanyl patch

Oral dose= 3x the iv dose

29
Q

Post operative analgesia?

A

If required i.v. in recovery 2mg increments every 3
minutes until comfortable (10 to 20mg) in a recovery
setting. Must be given by trained staff
Ward care: Morphine 10mg s.c. 3 hourly usually coprescribed antiemetic; Ondansetron or cycizine

Morphine Patient Controlled Analgesia:

  • Syringe driver intermittent i.v. bolus delivery initiated by patient (push button)
  • 1mg minimum frequency every FIVE minutes
  • Multiple studies show: approximately 1/3 dose compared to nurse administered s.c. morphine
30
Q

Routes of opioids administration?

A
  • Oral
  • i.v.
  • s.c. and i.m.
  • Rectal
  • Intrathecal
  • Epidural
  • Buccal
  • Trans dermal
31
Q

How to treat severe/chronic pain?

A
Oral morphine syrup or tablets
• Morphine s.c. infusion
• Diamorphine s.c. infusion
• Fentanyl transdermal patch lasts 5 days
• Buprenorphine patch
32
Q

What are Gabapentin and pregabalin?

A

Effective for chronic neurogenic pain
Reduce central transmission and pain projection
Aderse effect: sedation, dizziness, nausea, occasionally hypotension

33
Q

Examples of antidepressant drugs?
Uses?
Adverse effects?

A

Amitryptiline
Duloxetine & Citalopram
Useful adjuvant effects in neurogenic pain
Adverse effects - GI and CVS

34
Q

How to manage pain?

A

Assess severity on daily living and functioning

Amount of analgesia required to stop the pain = correct dose