7.9 (9.7) Adjuvant analgesics Flashcards
What is an adjuvant analgesic?
What are 3 clinical situations in which they can be used (if patient already on primary analgesic)
A medication with a primary indication other than pain but is useful as a coanalgesic during opioid therapy.
- Combine with primary analgesic to enhance pain relief
- Treat pain that is refractory to the analgesic
- Allow reduction in the opioid dose (to limit adverse side effects)
Combine, replace, reduce
List 4 ways to limit polypharmacy when using adjuvant analgesics
- Consider adjuvant only after opioid response ascertained
- Sequential drug trials to identify an effective drug. Initiate at low dose with gradual titration
- Only one drug added at a time
- Ineffective drugs should be stopped
FS:
- One drug at a time
- Sequential drug trial
- Optimize first drug before adding more drug
- Stop ineffective drugs
List 3 conventional pain etiologies benefiting from adjuvant analgesics
- Multipurpose
- Neuropathic pain
- Bone pain
- For pain/other symptoms in a bowel obstruction
Multipurpose adjuvant meds can be considered for diverse pain syndromes.
List 6 multipurpose adjuvant meds
- glucocorticoids
- alpha-2 adrenergic agonists
- cannabinoids
- topical therapies
- botulinum toxin
- neuroleptics
- NMDA inhibitors
FS:
1. Antidepressant (SNRI, TCA)
2. Anticonvulsant (gaba, lyrica)
3. NMDA antagonist (ketamine)
4. Na channel blocker (lidocaine)
5. Alpha 2 adrenergic agonist (clonidine, demedetomodine)
6. Steroids
7. CBD
When considering the use of an adjuvant analgesic a comprehensive assessment of the patient is required.
What are 3 elements of this assessment?
- Characteristics of the pain (LOPQRST)
- Impact of pain on function and quality of life
- Distinguish nociceptive or neuropathic pain
- Underlying etiology of pain
- Presence of associated factors (ie assess for total pain), including physical and psychological symptoms, functional impairments, psychiatric disorder, family or social disruption, financial problems, and spiritual or religious concerns, and their effects on quality of life.
FS:
LOPQRSTUV
DDX
Neuropathic vs nociceptive vs total pain
What three elements that make adjuvant analgesics less desirable than conventional analgesics such as opioids?
What is the implication of this for the use of adjuvant analgesics?
- Less efficacy- smaller proportion of treated patients who respond adequately
- Slower onset of analgesic effect (perhaps due to the need to initiate therapy at low doses to avoid side effects)
- More SEs
Most patients with moderate or severe pain related to serious medical illness should have opioids optimized FIRST before trying an adjuvant analgesic
What is sequential drug trial and why might this be required with adjuvant analgesia?
Sequential drug trials = only add 1 drug at a time, use low initial doses and gradual dose titration. Stop ineffective drugs
Why? Great patient variability in response to adjuvant analgesics and therefore inability to reliably predict the outcome of therapy
The process of sequential drug trials should be explained to the patient at the start of therapy to enhance adherence and reduce the distress that may occur as treatments fail.
Name six classes of adjuvant analgesics? Provide an example from each class
Table 7.9.1
Antidepressants- TCAs, SNRIs, SSRIs
Anticonvulsants- Gabapentin, pregabalin, topiramate, carbamazepine, phenytoin, valproate, oxcarbazepine, lamotrigine, levetiracetam
Alpha-2 adrenergic agonists - Clonidine, tizanidine, dexmedetomidone
Botulinum toxin - A, B
Cannabinoids - Tetrahydrocanninol (THC), nabilone, THC:cannabidiol mixture
Corticosteroids - Dex
N-methyl-D-aspartate receptor antagonists - Dextromethorphan, ketamine
Sodium channel blockers Mexiletine, tocainide, flecainide
Topical agents - Capsaicin, lidocaine patch, EMLA®
A. List 3 palliative symptoms for which RCTs support use of glucocorticoids.
B. A systematic review showed only weak evidence for analgesic efficacy of GCs - however clinical experience is positive. List 5 specific pain syndromes in which GCs seem helpful.
A. Anorexia, fatigue, nausea
B.
bone pain*
neuropathic pain*
pain from bowel/duct obstruction*
organ capsule expansion*
headache from raised ICP*
pain from lymphedema
target inflammation as 2ndary analgesia
- There is no data to inform choice of GC for pain. List 3 acceptable options.
- List 4 toxicities of GC.
- List 3 factors that increase the risk of GC associated toxicity
- Dexamethasone
Prednisone
Methylprednisone - Hyperglycemia
Myopathy
Osteoporosis
Psych disturbance (anxiety, psychosis) - Dose
Duration of therapy
Predisposing medical comorbidities
Antidepressants have been used as analgesics for decades. Can be considered for any type of chronic pain.
List 2 ways mood factors into considering antidepressants as an adjuvant for pain.
- Pain relief may be enhanced if there is positive mood effect
- But analgesia does not require mood change
- An early trial of antidepressant may be considered if comorbid depression
FS:
Improving mood = improving pain
Comorb depression
List 1 biological mechanism for how antidepressants (SNRI) may have analgesic effects
Enhanced availability of monoamines at synapses within descending pain modulating neural pathways (suppress pain signal transmission)
Ie - inhibiting the reuptake of these monoamines = more availability at synapses = descending inhibitory pain pathways are reinforced
List 2 classes of TCA’s and 1-2 examples of each
- Tertiary amine drugs:
- amitriptyline
- imipramine - Secondary amine drugs:
- desipramine
- nortriptyline
List 4 scenarios which warrant caution with TCA use
- significant heart disease
- risk factors for QTC prolongation
- Cognitive impairment
- Fall risk
- Acute close angled glaucoma
A patient has tolerated amitriptyline well but has only had partial relief despite the dose being at the maximum indicated for analgesic use.
* What should be done with the dose of this medication?
*What should be checked at relatively high doses?
* What type of TCA is amitriptyline and how does this differ from nortriptyline?
Given evidence of dose-dependent analgesic effects, it is reasonable to continue upward dose titration BEYOND usual analgesic doses in patients who fail to achieve benefit and have no limiting SEs. Note: there is no justification for increasing doses beyond the levels associated with antidepressant effects.
ECG to evaluate cardiac rhythm and QTC interval
Amitriptyline is a tertiary amine - more SEs, but better evidence for efficacy
Nortriptyline is a secondary amine - less SEs, but less evidence for efficacy
List two clinical contraindications for TCA
- narrow angle glaucoma
- recent MI
Note: caution in elderly, medically ill, CV disorders (QTC prolongation), seizure hx
List 4 side effects of TCAs (besides anticholinergic effects)
List 7 clinical findings of an anticholinergic toxidrome
Sedation, seizure, orthostatic hypotension, weight gain
Mad as hatter, blind as bat, red as beet, hot as hare, dry as bone, heart runs alone, bladder/bowel lose their tone
- How do SNRI’s compare with TCA’s re: side effects.
- i) What is the evidence for SNRI’s re: analgesic effect.
ii) Which SNRI is preferred? Name 3 SNRIs
iii) What is the approach to dose titration? - Give 2 examples of oncology treatment related pain syndromes and 1 SNRI shown to be helpful in each case
- How do SSRI’s compare with SNRI’s re: efficacy in pain
- SNRI’s have more favourable side effect profile than TCA’s
- There is high quality evidence for some SNRI’s - mainly duloxetine, venlafaxine, and desvenlafaxine.
Duloxetine preferred given number of positive trials.
Low starting doses overlap effective dose, so titration may or may not be needed.
Can increase if no s/e but stop at upper end of antidepress. range - i) CIPN - duloxetine 30-60 mg daily (cymbalata)
ii) Oxaliplatin induced PN - venlafaxine (Effexor)
iii) Post mastectomy pain - venlafaxine - Limited evidence for a few of the SSRI’s (paroxetine, citalopram, escitalopram) therefore SNRI’s chosen when primary indication of pain
List 4 side effects of SNRIs
Nausea, headache, somnolence, tremor, nervousness, hypertension, dry mouth, diaphoresis, constipation, sexual dysfunction.
Duloxetine: dizziness, fatigue
FS: NASH (nausea, anxiety, sexy dysfunction, headache)
List two clinical contraindications for buproprion (NDRI)
- seizure disorder (eg those with anorexia/bulimia)
- use of MAOI within 14 days (can cause hypertension and bupropion toxicity)
List four side effects of buproprion
Agitation, tremor, insomnia, nausea, decreased appetite, weight loss, headache, dry mouth, somnolence, hypertension, tachycardia
FS: NASH (nausea, anxiety, sexual dysfunction - although less than SSRI/SNRI, headache)
- List 2 examples of alpha adrenergic agonists + available routes + indication
- Describe their mechanism for analgesia
- Overall limited evidence for their use but:
Clonidine - orally, transdermally, epidural. Epidural clonidine effective for various cancer pain*
Tizanidine - oral antispasticity agent. s/e somnolence so can try 2-4 mg hs and uptitrate for pain complicated by insomnia
Dexmedetomidine - injectable sedative/hypnotic used in ICU. Evidence for pain/delirium in advanced illness*
- Activate monoamine-dependent endogenous pain modulating pathways in the brain and spinal cord (decrease pain transmission)
List three side effects of clonidine (alpha-2 adrenergic agonist)
somnolence, hypotension (usually orthostatic), and dry mouth.
tizandine - less often hypotensive due to less alpha 1 adrenergic activity
FS: think of dexmedetomidine and icu patients