intro to acute pain- analgesia choices
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Analgesia ChoicesHOW TO PLAN YOUR ANALGESIA FOR THE PATIENT
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
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
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
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
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
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
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
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
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
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
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