Introduction to pain and analgesics Flashcards
IASP definition of pain
pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms as such damage. Pain is perceived
what are the 3 pain fibers
1) Ab fiber
2) Ad fiber
3) C fiber
Ab pain fiber
- myelinated
- triggered with non-noxious stimuluses
Ad pain fiber
- myelinated
- triggered with noxious stimuluses
C pain fiber
- non myelinated
- dull achey pain
- triggered with noxious heat and chemical stimuli
where are the 3 areas that you can modulate pain CNS
1) dorsal horn
2) cortex
3) PAG
what are the two pathways
1) spinothalamic tract (ascending)
2) spinobulbar tract (descending)
where does the spinothalamic relay
conveys discriminative/localization aspects of pain by projection to the thalamus
where does the spinobulbar tract relay too
convays the affective/intensity aspects of pain and is able to recruit descending controls via the periaqueductal gray, pontine locus coeruleus and rostroventriomedial medulla
what are the types of chronic pain
- nocicpetive
- neuropathic
- mixed (nociceptive and neuropathic)
- visceral
examples of nociceptive chronic pain
OA and RA
examples of neuropathic pain
Central
- post-stoke
- MS
- SCI
- Phantom pain
Peripheral
- Post-herpetic neuralgia
- Diabetic neuropathy
- HIV related neuropathic pain
examples of mixed chronic pain
- Low back
- Cancer
- Fibromyalgia
examples of visceral chronic pain
- Internal organs
- Pancreatitis
- Inflammatory bowel syndrome
Physical sensations of neuropathic pain
- numbness
- tingling
- burning
- paresthetic
- paroxysmal
- lancinating
- electric like
- raw skin
- shooting
- deep, dull, bone like ache
Allodynia
Pain from a stimulus that does not normally provoke pain
Hyperalgesia
exaggerated response to a painful stimulus
Hyperesthesias
exaggerated response to touch
hyperpathy
persistant pain event after the cause of pain has been removed
what an analgesic
painkiller
is divided into 2 categories: nonopioid analgestics and opioid analgesics
nonopioid analgestics
are comprised of drugs such as acetaminophen, aspirin, ibubrofen
opioid analgestics
naturally occuring semisynthetic and synthetic agests are are characterized by their ability to relieve moderate to severe pain.
what analgestics modulate at the brain
- opioids
- NSAIDs
- Ketamine
- TCA
- Gabapentionoids
- Benzodiazepines
what analgestics modulate at the SC
- opioids
- neuraxial local anesthetics
- ketamine
- alpha- agonist
- TCA
what analgestics modulate at the peripheral nerve
- opioids
- TCA
- alpha agonist
- ketamine
- nerve block with local anaesthetic
what analgestics modulate at the tissue
- opioids
- NSAIDs
- local anesthetic infiltration
- corticosteroid
- cooling, immobilization, elevation
what conditions are muscle relaxants able to treat
hyper excitable skeletal muscle such as spasticity and muscle spasms.
where are the 3 areas that muscle relaxants can block at
1) SC level
2) neuromuscular junction
3) directly within the muscle fiber
what are some common symptoms of spasticity
- muscle stiffness
- muscle spasms
- rapid muscle contractions (clonus)
- fixed joints (contractures)
- exaggerated muscle jerks
- pain or tightness around joints
what is the primary goals for muscle relaxants?
1) decrease in skeletal muscle excitability
2) decrease pain
what are the 2 types of skeletal muscle relaxants
anti-spasticity or antispasmodic agents
what is labeled for use only in epilepsy and postherpetic neuralgia but is also used as a muscle relaxant?
Gabapentin
what is labeled only for the use of ALS but is also used as a muscle relaxant?
Riluzole
what are the most common anti-spasticity drugs
1) Baclofen
2) Dantrolene
3) Tizanidine
4) Botulinum toxin
what does Baclofen act on
Gaba-B receptors in the SC to inhibit reflexes and decrease spasticity
what does Dantrolene act on
directly on the skeletal muscles inhibiting Ca2+ release
what does Tizanidine act on
an alpha 2 adrenergic agonist that produces pre synaptic inhibition (CNS)
what does Botulinum Toxin work at
the neuromuscular junction inhibiting acetylcholine release
what are spasmolytics
muscle relaxants that inhibit muscle spasms (more for peripheral conditions)
what are common spasmolytics?
1) Carisoprodol (soma)
2) Cyclobenzaprine (flexeril)
3) Methocarbamol (robaxin)
4) Orphenadrine (norflex)
Carisoprodol (soma) acts on
believed to alter interneuronal activity in the SC and descending reticular formation.
Cyclobenzaprine (Flexeril) acts on
the CNS by decreasing the activity in the brainstem
Methocarbamol (Robaxin) acts on
the CNS
Orphenadrine (Norflex) acts on
has anticholinergic properties but unsure of direct effect
what are the key differences between anti-spasticity and spasmolytics?
- anti-spasticity: for CNS conditions with increased muscle tone, have more specific targets, more chronic in nature
- Spasmolytics: more PNS conditions, less clear targets, often used for acute conditions
what are polysynaptic inhibitors
same as spasmolytics; theorized to work on the reflex arc decreasing alpha motor neuron excitability and therefore cause muscle relaxation
what are the uses of polysynaptic inhibitors
- Adjunts to rest and PT for releif of muscle spasms associated with acute painful MSK injuries
- sometimes incorporated into the same tabel with an analgestic
what are the adverse affects of polysynaptic inhibitors
- drowsiness, dizziness
- nauseas, lightheadesness, vertigo, ataxia, headache
- tolerace and physical dependance
what are agents that are used to treat spasticity
1) Baclofen
2) Ticanidine
3) Dantrolene
4) Botulinum toxin
5) Gabapentin
6) Diazepam (benzodiazepines)
Diazepam (Valium) definition and what it works on
- benzodiazepine agent
- works by increasing the inhibitory effects at the CNS/SC synapses that use GABA. Less excited alpha motor neuron
what are the 6 intrinsic benzoduazepine effects
1) anxiolysis
2) anterograde
3) amnesia
4) sedation/hypnosis
5) anticonvulsant
6) antiemesis and muscle relaxation
what are the therapeutic uses of Diazepam (Valium)
- treating muscle spasms
- associated with inhibiting spasms of the larynx with the tentanus toxin
what are the adverse effects of Diazepam (Valium)
- sedation and reduction of psychomotor ability
- long term use can lead to tolerance and dependance
- sudden withdraw can lead to seizures, anxiety, agitation, tachycardia, and even death/coma
what is a drug that can be used to reduce the effects of Diazepam (Valium) overdose
Flumazenil
Baclofen (Lioresal) what is it and where does it effect
- Derivative of the central inhibitory GABA
- binds to GABA B receptors in the SC producing a less excited alpha motor neuron
what are the uses of Baclofen
- used to treat spasticity in SC lesions (paraplegia, quadriplegia, SC demyelination from MS)
- does not cause as much generalized muscle weakness
what are the adverse effects of Baclofen (Lioresal)
- drowsiness
- confusion and hallucinations
- nausea, muscular weakness, headache
what are the uses for Baclofen intrathecal (spinal) injections
- used for severe spasticity
- may decrease spasticity with a smaller dose with fewer systemic effects
what are the uses for intrathecal baclofen pump
able to adjust to deliver the drug at a slow continuous rate. achieves best clinical reduction in spasticity
intrathecal baclofen adverse effects
- pump malfunction can cause withdrawal symptoms
- increased delivery can cause overdose
- pt can build up tolerance to drug
what is the primary agent for adrenergic alpha 2 receptor agonists
Trizanidine (zanaflex)
what do adrenergic alpha-2 receptor agonists? Tizanidine (Zanaflex) work to do
- stimulate alpha 2 receptors in the spinal interneurons causing inhibition of the interneurons causing decrease in excitatory input to the alpha motor neurons
- decreases excitability at both the pre and post synaptic inhibition
what are the uses of Alpha-2 Agonists
- control spasticity from UMN lesions
- generally has milder side effects and produces less weakness
- Tizanidine better then Clonidine due to less side effects
what are the adverse effects of alpha-2 Agonists
- sedation, dizziness, dry mouth
- less generalized weakness
Gabapentin (Neurontin)
- developed as an anti-seizure med
- Enhances GABA effect in the SC
Uses of Gabapentin (Neurotin)
- decrease spasticity with SCI and MS
- best used in combo with other anti- spasticity agents
- might be helpful in reducing chronic pain
what are the adverse effects of Gabapentin (Neurotin)
sedation, fatigue, dizziness, ataxia
Dantrolene Sodium (Dantrium)
only direct muscle relaxant
what does Dantrolene Sodium (Dantrium) react on
inhibits the release of Ca2+ working directly on the sarcoplasmic reticulum
what are the uses in Dantrolene Sodium (Dantrium)
treating severe spasticity (UMN lesions)
what are the adverse effects of Dantrolene Sodium (Dantrium)
- generalized muscle weakness
- severe hepatotoxicity and fatal hepatitis
Botulinum toxin (Botox)
muscle paralytic injected locally
what are the serotypes of botulinum toxin
Type A (Botox) and Type B (Myobloc)
what are the limitations of botulinum toxin
- local irritation at injection
- have a limit of total dose
what is the mechanism of botox
inhibits Ach release at the NMJ causing paralysis within 3-7 days lasting 2-3 mo.
what are the effects of botox injection wearoff
a new presynaptic terminal sprouts with new source of Ach, need a new injection again
