Pain management Flashcards
principles of pain assessment:
- believe patients complain of pain
- use open ended questions
- Take history for each pain
- Look out for psychological distress – need to talk about subjective and psychological components
things to ask about when asking about pain:
site onset character radiation associations time course exacerbating/relieving factors severity
Goal of pain assessment
- Characterise and quantify pain
- Identify pain syndrome (acute, chronic, breakthrough, cancer related, non cancer related)
- Infer pathophysiology (nociceptive/neuropathic pain)
- evaluate physical and psychosocial comorbidities
- assess degree and nature of disability
- develop therapeutic strategy
examples of methods to characterise and quantify pain:
- Wong-baker faces rating scales
- FLACC scale (face, legs, activity, cry, consolability)
- Adjective rating scale
- Visual analog scale
- McGill-Melzack pain questionnaire
- Numerical rating scale
Some principles behind pain management
- Treat underlying causes when possible
- know what is pain mechanisms behind the pain
- Pharmacological treatments via WHO ladder
- treat according to specific guidelines
- Treat according to specific drug information
what are adjuvants:
analgesics that are non opioids/ drugs that are not primarily analgesics
General idea behind WHO treatment guidelines:
Match analgesic choice to severity of pain, titrate to response
- rapid titration for severe pain
- slower titration for moderate pain
- Even slower for mild pain
Specific guidelines for pain management:
- Mild pain (1-3)
- pt not on analgesics: begin with acetaminopen/NSAIDs; aspirin generally avoided due to irreversible antiplatelet effects
- pt on analgesics: titrate short-acting opioid, begin bowel regimen - Moderate pain (4-6)
- begin with weak opioid agonist - Severe pain (7-10)
- begin with strong opioid agonist
WHO treatment guidelines of analgesics
- Oral administration of analgesics
- analgesics given at regular intervals
- dosing adapted to individual
- analgesics prescribed acc to pain intensity as evaluated by scale of intensity of pain
- Analgesics prescribed with constant concern for detail
Max dose of paracetamol/day
4g/day
benefits of using paracetamol to manage pain:
low incidence of ADR, high oral/rectal availability, multi-preparation
limitations of using paracetamol to manage pain:
lack of inflammatory action – hepatotoxicity in large doses
Side effects of NSAIDs
- GI side effects, reversible platelet inhibition
- Renal: edema, HTN, renal failure
- CNS: HA, dizziness, nervousness, visual disturbances
- CVS: Edema, cerebrovascular accident, HTN, MI
- Hypersensitivity
- Hematological: Hemolytic anemia, pancytopenia, thrombocytopenia
Precautionary groups in the use of NSAIDs:
- elderly
- bleeding disorders
- asthma, bronchospasm
- GI disease (ulcers, bleeding)
- CVD
- Renal/hepatic dysfunction
- Receiving anticoagulants
DDI with NSAIDs:
- Increased risk of bleeding:
- anticoagulants, antiplatelet drugs (ticlopidine, clopidogrel, aspirinm abciximab, dipyridamole, eptifibatide, tirofiban) - Increased risk of nephrotoxicity (ACEi, ciclosporin, tacrolimus, diuretics)
- Increased risk of GI ulceration (corticosteroids)
- Decreased antihypertensive effects (ACEi, BB, diuretics)
- increase potential adverse effects of chemo
Adjuvants used in neuropathic pain:
Gabapentin, pregabalin, antidepressants, antiepileptics, topical lidocaine
What type of pain is corticosteroids commonly used as adjuvants for?
Bone pain, neuropathic pain, raised intracranial pressure, liver capsule stretch pain
what is hyosciene butylbromide usually used as adjuvants for?
intestinal colic
adjuvants used in bone pain:
corticosteroids, NSAIDs, bisphosphonates
adjuvants used in cramps/muscle spasms:
Muscle relaxants
MoA of opioids:
analgesic effect through ≥4 groups of receptors and other subpopulations – receptors in brain, spinal cord, peripheral sensory neurons and intestinal tract
Affinity of codeine phosphate to opioid receptors:
low
Dosage forms of codeine phosphate that are available
Injection
Tablet
conversion of codeine to morphine (including dosage form)
200mg (PO) codeine = 10mg (SC/IV) morphine = 100mg (IV) codeine
dosing adjustment in renal impairment for codeine phosphate:
Clcr = 10-50mL/min : 75% of dose
Clcr < 10mL/min: 50% of dose
potential DDI of codeine phosphate:
substrates of CYP2D6, 3A4, and inhibitors of CYP 2D6 will decrease effects of codeine:
- chlorpromazine, fluoxetine, miconazole, paroxetine, quinidine, quinine
Adverse reactions of codeine phosphate:
Drowsiness, constipation
MoAs of Tramadol:
opioid agonist, inhibition of reuptake of NA and serotonin
Benefits of Tramadol over other opiates:
- Less SE: CV and Resp
2. Lower abuse potential
Available forms of tramadol:
Injection and tablet
dose conversion of tramadol
50mg of tramadol=60mg codeine
120mg tramadol = 30mg oral morphine
dose adjustment of tramadol (renal)
imm release: Clcr=<30mL/min: 50-100mg dose q12h (max 200mg/day) – original is q4-6, max 400mg
extended release: Clcr= <30mL/min: do not use
dose adjustment of tramadol (hepatic)
imm release: Cirrhosis: 50mg q12h
extended release: Not used in severe hepatic dysfunction
Adverse effects of tramadol:
Incidence of some increase over time
- dizziness, HA, somnolence
- Constipation, nausea (GI)
lower seizure threshold at high dosing – avoid use in patients predisposed to epileptic activity
DDI of tramadol:
- Substrates of CYP 2D6, 3A4: decrease effects of tramadol
- chlorpromazine, fluoxetine, miconazole, paroxetine, quinidine, quinine
- carbamazepine: decrease half-life of tramadol - Naloxone: increase risk of seizures in tramadol overdose
- Neuroleptic agents: increased risk of tramadol-associated seizures (additive CNS depressant effects)
- SSRIs: increased risk of seizures –> citalopram, fluoxetine, paroxetine, sertraline
- TCAs: increased risk of seizures
- Warfarin: increased PT, monitor
available dosage forms of morphine:
PO, IV, IM, SC, I/T, epidural
Oral: Paranteral ratio for dose of Morphine
2(3):1
dosing adjustment in renal impairment for morphine:
Clcr 10-50mL/min: 75% normal dose
Clcr<10mL/min: 50% normal dose
Notable adverse events in the use of morphine:
- CV: hypotension, palpitaions, bradycardia
- CNS: Drowsiness (tolerance in 1-2 weeks), confusion, HA
- Dermatologic: Pruritis (may be secondary to histamine release)
- GI: Nausea (tolerance in 1-2 weeks), constipation, xerostomia
- Genitourinary: urinary retention (up to 20 hrs)
- NM and skeletal: weakness
DDI & FDI with morphine use:
- Antipsychotic agents: May increase hypotensive effects of morphine
- CNS depressants: increase effects/ toxicity of morphine
- MAOi: increase effects/toxicity –> avoid use within 14 days of MAOi
- Ethanol: increase CNS depression
- Avoid: valerian, St. John’s wort, kava kava, gotu kola (increase CNS depression)
- Food: administration of oral morphine with food may increase bioavailability
Dosage forms of fentanyl:
injection, dermal patch
Dose conversion of fentanyl:
100mcg (IM) fentanyl = 10mg (IM) morphine
i.e. 1:100
Side effects of fentanyl:
- CV: hypotension, bradycardia
- CNS: CNS depression, confusion, drowsiness, sedation
- GI: N/V, constipation, xerostomia
- Respiratory: respiratory depression
Withdrawal sx when changed from morphine PO to TD fentanyl:
- GI: colic, diarrhea, nausea
- Sweating,
- Restlessness
Caution when using TD fentanyl:
- used patch still contain drug – need to fold patch with adhesive side inward before disposal
- Rate of absorption of fentanyl from patch may be increased in febrile patients/if skin under patch becomes vasodilated because of external heat source (do not use them)
MoAs of methadone:
- µ-receptor agonist
- NMDA receptor channel blocker
- presynaptic blocker of serotonin re-uptake (SSRI)
DDI & FDI of methadone:
- CYP3A4 inducers: decrease levels/effects of methadone (aminoglutethimide, carbamazepine, phenobarbital, phenytoin, rifamycins)
- CYP3A4 inhibitors: Increase levels/effects of methadone (azole antifungals, clarithromycin, diclofenac, doxycycline, erythromycin, imatinib, isoniazid, nicardipine, propofol, quinidine, verapamil)
- Agonist/antagonist analgesics: decrease analgesic effect of methadone and precipitate withdrawal symptoms (buprenorphine, butorphanol, nalbuphine, pentazocine)
- Ethanol: avoid as may increase CNS effects
- Avoid St John’s wort (decrease methadone levels, increase CNS depression) , valerian, kava kava, gotu kola (increases CNS depression)
- Grapefruit juice
Renal and Hepatic Dose adjustment in methadone:
Clcr<10mL/min: 50-75% normal dose
avoid in severe liver disease
side effects of methadone:
May decrease over several weeks (constipation and sweating may persist)
1. CV: bradycardia, peripheral vasodilation, hypotension, tachycardia, cardiomyopathy, flushing, heart failure, palpitation
2. CNS: euphoria, dysphoria, HA, insomnia, agitation, disorientation, drowsiness, dizziness, lightheadedness, sedation, confusion, seizure
3. Dermatologic: pruritus, urticaria, rash
4, GI: N/V, constipation, anorexia, stomach cramps, xerostomia, biliary tract spasm, abdominal pain, glossitis, weight gain
5. Genitourinary: urinary retention/hesitancy, impotence
6. Hematologic: Thrombopenia (reversible)
7. NM disturbances
8. Occular: miosis, visual disturbances
9. Respiratory: respiratory depression, respiratory arrest, pulmonary edema
Starting doses of oxycodone for its different preparations:
- Imm release: adults 5mg q6h PRN
- Controlled release: adults (opioid naive) 10mg q12 h
- normal released used in the same way as morphine but q6h rather than q4h
Hepatic/Renal Dosing adjustment in oxycodone:
- Severe liver disease: Decrease dose
2. Renal impairment: use with caution
Side effects of use in oxycodone:
- CNS: Fatigue, drowsiness, dizziness, somnolence
- Dermatologic: pruritus
- GI: N/V, constipation
- NM and skeletal: weakness
DDI/FDI in use of oxycodone:
- CYP2D6 inhibitors: decrease effects of oxycodone (chlorpromazine, fluoxetine, miconazole, paroxetine, quinidine, quinine
- Ethanol: increase CNS depression
- Food: high fat meal
- avoid: valerian, St John’s wort, kava kava, gotu kola (increase CNS depression)
MoA of tapentadol:
- µ-receptor agonist
2. NARI
Important points in administering Tapentadol
PO 50-100mg q4-6h with/without food
- Long acting formulations must be swallowed whole
dose of tapentadol in management of moderate-severe acute pain in adults:
50-100mg administered q4-6 h depending on intensity of pain
Side effects of tapentadol:
- CNS: dizziness, drowsiness
2. GI: N/V
Partial agonist of opioid receptors:
buprenorphine
mixed antagonist agonist of opioid receptors:
Pentazocin (agonist against kappa, antagonist against mu)
benefits of using pethidine over morphine:
Less prominent effects on CVS and GIT
dose conversion of pethidine:
75mg (IV) pethidine =10mg (IM/SC) morphine
Dose of pethidine for acute pain:
IV 75mg-100mg q3h
dose adjustments in pethidine use:
decrease dose in hepatic impairment (cirrhosis)
Clcr: 10-50 mL/min: 75% of normal dose
Clcr: <10mL/min: 50% of normal dose
Side effects of pethidine:
- CV: hypotension
- CNS: fatigue, drowsiness, dizziness, nervousness, HA, restlessness, malaise, confusion, mental depression, hallucinations, paradoxical CNS stimulation, Increased intracranial pressure, seizure, serotonin syndrome
- Dermatologic: rash, urticaria
- GI: N/V, constipation, anorexia, stomach cramps, xerostomia, biliary spasm, paralytic ileus, sphincter of oddi spasm
- Genitourinary: ureteral spasms, decreased urinations
- Local: pain at injection site
- NM and skeletal: weakness
- Respiratory: dyspnea
Why is pethidine avoided in palliative care:
increased risk of dependence
toxic metabolite (norpethidine) that accumulates if given regularly – decreased seizure threshold
more emetogenic than morphine
Exceptions when calculating for equivalency:
- morphine –> TD fentanyl: no reduction
- severe pain, no need reduction
- converting to methadone: larger reduction (75%-90%) depending on dose of prior opioid
- Elderly patients/ those with organ dysfunction – consider reduction
Steps for opioid dose reduction:
- calculate total daily dose
- Calculate breakthrough dose (1/6 of total daily opioid dose given only when patient experiences pain)
- Switch to SR preparation when patient stabilised on current dose (morphine sustained release 500mg q12h)
Steps when starting patient on morphine:
- if pt previously receiving weak opioid, give q4h or modified release 20-30mg q12h
- if changing from alternative strong opioid (fentanyl, methadone), much higher dose may be needed
- if pt is frail and elderly, decrease dose to help reduce initial drowsiness, confusion and unsteadiness (5mg q4h)
- renal failure: decreased dose or decreased frequency of dose due to accumulation of active metabolite
Steps when starting patient on Morphine
- if pt taking 2 or more PRN doses in 24 hr, regular dose increase by 30-50%
- upward titration of dose stops when either pain relieved/intolerable side effects – aim to have pt free of pain and mentally alert
- m/r morphine may not be satisfactory in pt. troubled by frequent V/D/ileostomy (poor absorption) – use with caution if have renal impairment
Dose of naloxone:
Adult (IV): 100-200mcg adjusted acc to response – repeat every 2 mins
Max 10mg if respiratory function does not improve
Child (IV): 50-10mcg/kg, may be repeated every 2 min
When a patient shows sign of opioid overdose/toxicity, what are the ways to manage it according to the severity of symptoms?
- If RR ≥8/min and easily arousable and not cyanosed, wait and see – consider reducing/omitting next regular dose of morphine
- If RR< 8/mi, patient barely rousable/unconscious and/or cyanosed:
- dilute standard ampoule containing naloxone 400mcg to 10mL with saline for injection
- administer 0.5mL (20mcg) IV every 2 min until respiratory status satisfactory
- further boluses may be needed cos it is shorter acting than morphine
Side effects that are shared among most opioids
Common: N/V, constipation, somnolence, mental clouding
Less common: myoclonus, respiratory depression, postural hypotension, itch/rash, urinary retention
3 approaches to treat opioid adverse effects:
1 dose reduction + use of adjuvants
- changing to diff opioid/route of administration
- Symptomatic management
Symptomatic management of opioid side effects
- N/V, constipation
- Sedation and cognitive dysfunction: Psychostimulants (caffeine 100-200mg PO/day, dextroamphetamine 2.5-10 mg PO BD, methylphenidate 5-10mg PO BD)
- pruritis
- myoclonus (clonazepam 0.5-2mg PO BD or other anticonvulsants)
Clinical outcomes of opioid therapy (i.e. goals and monitoring?)
- Pain relief
- Side effects
- Function (physical and psychosocial)
- Drug-related behaviours
Describe tolerance in opioid therapy:
- decreased drug effect from drug exposure
- can be associative (learnt) or pharmacologic (due to PK/PD changes)
- tolerance to side effects desirable
- tolerance to analgesia seldom a problem in clinical setting
Describe Addiction in opioid therapy:
defined by behavioural phenomena:
- loss of control
- compulsive use
- use despite harm
diagnosed by observation of aberrant drug-related behaviour
describe pseudo-addiction in opioid therapy:
- aberrant drug-related behaviours driven by desperation over uncontrolled pain
- prevent by increasing pain control
- need to consider complexities
Risk of addiction to opioids based on use, in different types of pain, or pain settings
- acute pain: very unlikely
- cancer pain: very unlikely
- Chronic non-cancer pain: mixed results – prevent addiction using opioid contract to withdraw treatment at any sign of abuse