Pain Management (Part 2) Flashcards
1
Q
Characteristics of paracetamol:
- drug class
- dosing
- benefits and side effects
A
- most commonly used type of NSAIDs
- 500-1000mg Q4H-6H per day, maximum 4g/day. For chronic administration, consider not more than 3g/day.
- (+) - few side effects
(-): hepatotoxic, especially if administered >4g/day
2
Q
Explain the principles behind choice of NSAIDs
A
- if patient has previously taken NSAIDs and it has worked well for him, continue to administer the same NSAID
- If patient has not taken NSAIDs before, administer ibuprofen as first line.
- If patient has taken two NSAIDs and they have not worked well for him, consider switching to another drug class.
- Selective COXIBs have lower incidence of GI side effects, inhibit platelet aggregation. Topical NSAID - patch
3
Q
Precautions in taking NSAIDs
A
- Elderly (>65 years old)
- Bleeding disorder
- Anticoagulants
- Cardioavascular disease
- GI ulceration
- renal and hepatic dysfunction
- bronchospasm, asthma
4
Q
Drug interactions with NSAIDs
A
- GI ulceration (corticosteroids)
- Increase risk of bleeding
- contraindicated with warfarin, LMWH, heparin
- clopidogrel, ticlopidine, aspirin, abciximab - Increased risk of nephrotoxicity
- ciclosporin, tacrolimus, ACE inhibitors - Reduced antihypertensive effects (ACE inhibitors, ARB, diuretics)
5
Q
Adjuvants and their indications
- pregabalin, gabapentin, antidepressants, antiepileptics, topical lidocaine
- corticosteroids
- NSAIDs
- Benzodiazepines
- Hyoscine
A
- neuropathic pain
- neuropathic pain, bone pain, intracranial pressure etc.
- bone pain
- muscle cramps and spasm
- intestinal colic
6
Q
Mu receptor effects
A
mu(1): analgesia
mu(2): side effects
7
Q
Opioids mechanism
A
- modifies central perception of pain
- synergistic with non-opioids
- likely to be a controlled substance
8
Q
Classification of opioids by pain intensity
A
Weak:
- codeine
- tramadol
Moderate:
- tapentadol
Strong:
- morphine sulphate
- fentanyl
- pethidine
- methadone
- oxycodone
9
Q
Characteristics of codeine:
- Onset and duration of action
- Equianalgesic dose
- Dose
- Renal and hepatic dosing adjustment
- Drug interactions
A
- fast onset of action and short duration
- 200mg PO codeine = 100mg IV codeine = 10mg IM/SC morphine
- 15mg - 60mg 6 times daily
- Hepatic dosing adjustment is necessary
Renal dosing adjustment:
CrCL 10-50mL/minute: administer 75% of dose
CrCL <10mL/minute: administer 50% of dose - CYP2D6 substrate (major), CYP3A4 (minor) –> chlorpromazine, fluoxetine
10
Q
Characteristics of tramadol:
- MOA
- Dose
- Renal and hepatic dose adjustment
- Adverse reaction precaution
- Drug interaction
A
- analog of codeine, similar potency. opioids agonist, reuptake of noradrenaline and serotonin.
- Dose: 50-100mg Q4-6H, max 400mg/day
3a. Renal (CrCl <30mL/minute): 50-100mg Q12H (half dosing)
3b. Hepatic (cirrhosis): 50mg Q12H.
» extended release should not be used in patients with CrCl <30mL/minute, and with severe hepatic dysfunction.
- At high dosing, seizure threshold is lowered (don’t give to those on antiepileptic medication)
- CYP2D6 substrate (major), CYP3A4 (minor) –> chlorpromazine, fluoxetine
naloxone, neuroepileptic agents, SSRIs, TCAs- increase risk of seizures
warfarin - concomitant use may lead to elevation of prothrombin times, monitor
11
Q
Characteristics of morphine:
- Opioid strength
- Availability of dosage forms
- Dose
- Dose adjustment in renal and hepatic impairment
- Drug interactions
A
- Strong opioid
- Wide range of dosage forms and administration routes, can be given as epidural as well.
- Varies
For those on starting dose and who were previously receiving weak opioid, give 10mg q4h . Frail and elderly: 5mg q4h. - CrCl 10 - 50mL/minute: administer at 75% of normal dose | CrCl < 10mL/minute: administer at 50% of normal dose
Unchanged in mild liver disease - Antipsychotic agents, MAOIs, CNS depressants: increase toxicity of morphine
Avoid ethanol, herb (St. John’s wort), administration with food.
12
Q
Fentanyl characteristics
- Drug class and strength
- Dose
- Renal and hepatic dosing adjustment
A
- semi-synthetic opioid, super strong (100 times more potent than morphine)
- 100mcg (IM) fentanyl = 10mg (IM) morphine
Dose: 50-100mcg/kg - No need for dose adjustment for renal impairment, monitor for dose adjustment for hepatic impairment.
13
Q
Transdermal Fentanyl:
- MOA
- Indications
- PK
- Other observations
A
- Self-adhesive skin patch with a rate-limiting membrane allows a standardised amount of fentanyl to cross each hour from the patch to the skin.
- Indicated for patients with:
- intolerable undesirable side effects from morphine
- renal failure
- dysphagia
- ‘tablet phobia’ or poor oral compliance - high bioavailability
- patients may experience withdrawal syndrome when changed from PO morphine to TD fentanyl. Probably due to impact on peripheral and central mu-opioid receptors as well.
14
Q
Methadone:
- MOA
- Drug interactions
- Renal and hepatic dose adjustment
A
- mu-opioid receptor agonist, NMDA receptor channel blocker, presynaptic blocker of serotonin re-uptake
- CYP3A4 (major), ethanol, herb
- Dose adjustment in renal impairment
- CrCl <10mL/minute: administer 50% to 75% of normal dose
- avoid in severe liver disease
15
Q
Oxycodone:
- Dose
- Dose adjustment for renal and hepatic dysfunction
- Drug interactions
A
used as an alternative to morphine.
- Dose varies like morphine, but it is taken every 6 hours instead of 4 hourly for morphine.
- Use with caution in patients with renal impairment, reduce dosage in patients with severe liver disease.
- substrate of CYP3A4 and CYP2D6, avoid ethanol, St John’s Wort, food.
