intro to acute pain- analgesia choices
TRANSCRIPT
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Analgesia ChoicesHOW TO PLAN YOUR ANALGESIA FOR THE PATIENT
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WHO Analgesic Ladder Analgesic framework proposed by WHO in 1986 For treatment of cancer pain Recommendations still relevant, & can be
extended to treatment of pain in general
Step 1- Non-OpioidsParacetamolNSAIDs/ COX-2+ Adjuvants
Step 2- Weak OpioidsCodeineTramadolBuprenorphine+ Adjuvants
Step 3- Strong OpioidsMorphineOxycodoneFentanylMethadone+ Adjuvants
Pain ↑ or persists
Pain ↑ or persists
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WHO Analgesic Ladder 1. Oral route whenever possible 2. Administer at regular intervals 3. Prescribed according to pain intensity
If severe pain: additional analgesics made available as rescue analgesics (PRN on pt request)
4. Dosing should be individualised Age, renal/ hepatic function, side effect profile
5. Analgesic regime explained clearly to pt & staff Ask for PRN analgesics early rather than late Take xx mins prior to PT/OT
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Analgesic Choices 1 1. PK considerations
Oral route is preferred Fast onset needed for severe acute pain (may need parenteral
route) Regular analgesia if pain expected to persist
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Analgesic Choices 2 2. Side effect profile of patient
Simple analgesics eg. Paracetamol, have minimal side effects (within appropriate dosing), hence good as part of multimodal analgesia
Peptic ulcer disease: Coxibs slightly lower risk vs non-selective NSAIDs Risk of renal impairment/ existing renal impairment:
NSAIDs: Avoid Opioids: Dose adjustment needed for morphine
Hepatic impairment Paracetamol: Generally safe, consider ↓ dose or ↓ frequency if chronic use NSAIDs: Metabolised by liver, can use in mild liver disease. Avoid in cirrhosis Opioids: No dose adjustment needed for morphine or fentanyl
Opioid adverse effects Risk of opioid induced respiratory depression: elderly, renal impaired, OSA, obesity,
opioid-naive Tolerance to other opioid side effects: nausea, vomiting, giddiness, constipation
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Analgesic Choices- Coxibs vs Non-selective NSAIDs Most side effects are dose-dependent Peptic ulcer disease
Generally lower in Coxibs: endoscopic & clinical outcomes (symptomatic ulcers/ ulcer complications)
May be similar in Coxibs + aspirin vs Non-selective NSAIDs Renal impairment
Coxibs & NSAIDs NOT recommended for at risk group: chronic renal insufficiency, DM nephropathy, volume depleted, CVS Dz/ CCF, concurrent use of meds that impair potassium excretion
Platelet function: Coxibs do not inhibit platelet function ↑ safety in anticoagulated patients eg. those on warfarin for PE
CVS disease Worsen CCF, ↑ BP: both Coxibs & Non-selective NSAIDs Ischaemic CVS events: May be ↑ in Coxibs as they do not inhibit platelet fx
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Practical PK Non-opioidsPK Parameters Diclofenac Naproxen Celecoxib Etoricoxib KetorolacDose (max/d)
PO 50mg tds (100-150mg/d)PO SR 75-100mg bd (150-200mg/d)
PO 275/ 550mg bd (1100mg/d)
PO 100/ 200mg bd (400mg/d)
PO 60/90/120mg om (120mg/d)
IM 30/ 60mg (120mg/d)
Time to peak serum (mins)
IM 5 NA NA NA 30-60PO 15-30 60-120 180 60 45PO SR 120-300 240-360 NA NA NAPR < 60 NA NA NA NA
Protein bind (%) albumin, > 99 albumin, > 99 albumin, 97 92 99Metabolism
Hepatic HepaticHepatic, CYP2C9 Hepatic Hepatic
Active metabolites weak inactive inactive weak ?Bioavailability (%) 55 100 unknown 100 100Elimination T1/2 (mins)
IM 60-120 NA NA NA 300PO 120 720-1020 180-600 1200
Duration action (hrs) < 8 < 12 < 12 24 4-6
Source: UpToDate. May differ from other sources due to different parameters: eg different bolus doses, or time to serum peak vs time to peak effect
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Analgesic Choices- Opioids
Most side effects are dose-dependent Consider dose-reduction if intolerable nausea, giddiness
Tolerance develops for most side effects except constipation Always monitor BO, prescribe laxatives
Desaturation is a late sign of respiratory depression, ↓ RR is an early sign O2 therapy, monitoring in at risk group
Needs renal dose adjustment
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Practical PK OpioidsPK Parameters Morphine Oxycodone Pethidine Tramadol FentanylReceptor actions
mu, k, d mu, k, dmu, k, anti-muscarini, LA
mu, k, d, presynp 5HT release mu, k, d
Common Dosing PO 5mg 6H PRN,IV PCA PO 5mg 6H PRN IM/ IV 25-50mg
PO 50mg 8HIM/ IV 25-50mg SC or as IV PCA
Potency1
1 (IV)1.5 (PO) 0.1 0.1 100
Onset (min) PO IR 30 10-15 NA 60 NAIV 5-10 ? 5 ? 2-3
Time to peak serum (min)
PO IRNA
60-120 (cap)< 60 (liquid) NA 120 NA
PO SR 180-240 240-300 NA NA NASC 50-90 No data, but
should approximate morphine
60 NA No dataIM 30-60 60 45 NAIV 20 10 ? 3-4TD NA NA NA NA 18
Bioavailability (%) 17-33 60-87 20 75 50-70Duration (hrs) PO IR,
IM, IV 3-5 3-6 2-4 6 0.5-1PO SR 8-12 12 NA NA NA
Source: UpToDate. May differ from other sources due to different parameters: eg different bolus doses, or time to serum peak vs time to peak effect
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How To Write Analgesic Prescriptions 1. Route = oral whenever possible
2. Drug Name 3. Dosage
Paediatric pt, liver/ renal impairment may need dose adjustment
4. Frequency Regular Intervals, if pain expected to persists. Eg x no of
times a day or x hourly Rescue Analgesics, if severe pain flares expected. Use
“PRN” (Pro Re Nata, Latin for as the circumstance arises) Examples:
PO Paracetamol 1g QDS PO Tramadol 50mg 8H PRN (for severe pain) PO Maxolon 10mg 8H PRN (for nausea, vomiting)
Frequency Abbrev.Every morning
OM
Every night ON1x a day OD2x a day BD3x a day TDS4x a day QDS8 hourly 8H
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Analgesic Choices- Opioids as PCA
Responsibility of Acute Pain Service (Anaesthesia Department): patient/ programme selection
Most common PCA opioid = IV Morphine Advantages of Patient-Controlled Analgesia
↓ delay in analgesia delivery: do not need to request to nurse, wait for nurse to check & administer controlled drug
↓ respiratory depression: patient will not press when drowsy IV route more potent vs oral, faster onset Provides sense of control over pain to patient
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IV PCA Morphine Common IV PCA Morphine Setting
Concentration: 1mg/ml Reservoir: 50ml or 100ml Bolus: 1mg Lockout: 5min Basal infusion: 0mg/hr Max: 6-10 doses/hr