Analgesics- Local and NSAIDs Flashcards
The detection of a noxious stimulus at the tissue
Nociception
Free nerve endings of primary afferent neurons that detect noxious stimuli
Nociceptors
What are the 5 processes that play a role in nocicpetion
Transduction -> stimuli to AP Transmission -> peripheral nerves to CNS Modulation ->dorsal horn of spinal cord Projection ->2nd order to thalamus Perception -> integration
What are the types of primary sensory nocicpetion nerve fibers
AB fibers
A-delta (pinpoint; mechanical/thermal)
C-fibers (diffuse; many stimuli )
Pain that persists longer than it is providing protection
Chronic pain
Exaggerated perception of pain produced by a noxious stimuli
Hyperalgesia
Primary-> occurs in area of tissue damage
Secondary-> occurs beyond region of injury
non-noxious stimuli that elicits pain
Allodynia
________________ activate nociceptors
Inflammatory mediators
Pain receptor change from high to low threshold
Primary hyperalgesia
Inflammatory mediators activate more nociceptors adjacent to injury
Secondary hyperalgesia
Where does central pain sensitization occur and what receptors are involved
Dorsal horn of the spinal cord
NMDA receptors
What is pain sensitization
Changes occur in sensory processing enabling low intensity stimuli to produce pain.
NMDA and Glutamate - increase in excitatory neurotransmitters cause hyper-excitability in dorsal horn neuron
Occurs in acute and chronic pain
What receptor plays a central role in chronic pain
NMDA receptor
What is the main effect of local anesthetic?
Reversible blockade of transmission
What drugs can be used for local anesthesia
Lidocaine Bupivicaine Mepivicaine Ropivicaine Proparacaine Procaine
Local anesthetics belong to what two chemical groups
Amides
Esters
Are local anesthetics weak bases or acids?
Weak bases
What are the amide local anesthetics ?
Lidocaine
Bupivacaine
Mepivacaine
Metabolized in the liver
What are the ester local anesthetics
Procaine
Proparacaine
Hydrolyzed by plasma esterases
What is the MOA of local anesthetics?
Cross lipid membrane of nerve cell into the cytoplasm
Prevent depolarization and block the propagation of an action potential by inhibiting the influx of sodium
What is the onset of blockade of local anesthetics??
Small. Myelinated A-delta fibers (sensory)
Unmyelinated C fibers (sensory/autonomic)
Large myelinated Aa fibers(motor)
The effect of local anesthetic is usually terminated by ____________
Redistribution
Why would you use epinephrine in conjunction with a local anesthetic
Epinephrine causes vasoconstriction which decreases the distribution of the anesthetic from its site of action => longer lasting effect
The duration of a local anesthetic will be affected by?
Lipophilicity
Ability to bind sodium channel
Underlying disease -> hepatic disease=increased duration of amides
Drug-drug interaction
Esters are broken down by?
Plasma esterases
Where are amides metabolized
Liver
Where are local anesthetic metabolites excreted
Urine
How does the half life of esters compare to amide local anesthetics?
Esters- few minutes; rapidly broken down by plasma cholinestersase
Amides- hours (2-6); metabolized in the liver
Increasing the _______________ of urine will increase local anesthetic elimination
Acidity
Local anesthetics are all weak bases
What routes of administration can be used for local anesthetics?
Topical - skin/wound/splash block
Local infiltration -peripheral nerve block/intra-aricular/epidural
Intravenous -Bier’s block
What are the clinical uses of local anesthetics?
Regional anesthesia
Pre and post-operative analgesia
Wound management
Peri-operative analgesia
When is regional anesthesia used?
Minor procedures
Lameness localization
Epidural
-completely block nociception at site of injury or surgery
What kind of regional analgesia can be used for injury/surgery distal to the elbow
Brachial plexus block
What kind of regional analgesia could be used for thoracotomy, chest tube, or rib fractures
Intercostal nerve block
Injections -> three ribs anterior and two ribs posterior to site of injury
What are the benefits to regional analgesia ?
Less sedation Decreased nausea and vomiting Decreased CV and pulmonary complications Shorter hospitalization Decreased infection Decreased morbidity and mortality
What are the major risks of using regional analgesia?
Local anesthetic toxicity
Nerve injury
-trauma, toxicity, ischemia, or combination ->result from needle, intraneural injection, compression, or stretch
What are the contraindications to using epidurals
Coagulopathy
Anatomy
Skin infection/ sepsis
Neurological disease
What are the complications that can arise from an epidural
Horners Hypotension Hypoventilation Schiff-Sherrington Muscle twitching Hypoglycemia Urinary retention
What is the most commonly used local anesthetic in vet med
Lidocaine
What is the onset of action and duration of lidocaine?
Rapid onset -5mins
Duration -40-60mins
Lidocaine is metabolized where
Liver
What animals are sensitive to lidocaine
Do not exceed 4-7mg/kg
Cats more than dogs
Sheep may be more sensitive than other livestock
_______________ is used as a topical gel/ointment for dermal analgesia
5% ELMA cream (2.5%lidocaine / 2.5% prilocaine)
What is a lidocaine solution for injection
Lidocaine (Xylocaine) -local use
What are the clinical uses of lidocaine?
Systemic Antiarrhythic (IV)- class 1B antiarrhythmic- control arrhythmias
Preanesthetic (IV)
Analgesic with anti-inflammatory properties
Antioxidant
GI prokinestic -increase GI motility in horses
What is the most cardiotoxic of the local anesthetics?
Bupivacaine
Local anesthetic that is infused through thoracostomy tubes or wound soaker catheters
Bupivacaine
What is a precaution to using Bupivacaine?
Cardiotoxic
->Should not used in patients post pericardectomy
Phrenic nerve paresis or paralysis
Why do cats generally have lower dose of analgesics than dogs?
Cats are deficient in hepatic metabolism
Sensitive to anesthetics
Amides are degraded in the liverr
What is the drug of choice for diagnostic nerve blocks in horses
Mepivacaine
How does the duration of action differ between the amide anesthetics?
Lidocaine < Mepivicaine < Bupivicaine
What local anesthetic is used topically for corneal and conjunctival manipulation
Proparacaine
What is the onset and duration of proparacaine?
Rapid (30sec) Short duration (10-20mins)
What are the contraindications to proparacaine use?
Long term corneal use –> toxic
What ester anesthetic is a class 1a antiarrhythmic
Procainamide
What ester analgesic is not used as a local anesthetic but is present in some Penicillin G preparations
Procaine
What ester analgesic is VERY toxic to cats and can cause Heinz body anemia and blood dyscrasia
Benzocaine
What nociception process is least affected by the administration of local anesthetic drugs ?
Perception
Projection
What two nocicpetion processes are affected by NSAIDs ?
Transduction and modulation
What is the main effect of NSAID
Inhibiting cyclooxygenase (COX) enzymes
What is the role of COX1 enzyme
Production of prostaglandins
Mediates Thromboxane A2 -> platelet aggregation
Prostaglandin E1 -> maintain GI mucosa
What is the role of COX2
Production of prostaglandin in times of inflammation
what are the COX2 selective inhibiton NSAID
Carprofen Derocoxib Robenacoxib Firocoxib Meloxicam Piroxicam
What are the non-selective COX1 and COX2 inhibitors
Phenylbutazone
Flunixin meglumine
What is a selective COX1 inhibitor
Aspirin
T/F: NSAID are all weak bases
F
Weak acids
What are the 4 effects of NSAIDs
Anti-inflammatory -> inhibit eicosanoids synthesis (thromboxane, prostacyclin, and prostaglandin)
Analgesic -> decrease PG sensitization of neurons
Antipyretic -> reduce fever
Antiendotoxic (if given before endotoxic challenge)
What is the strongest acid of NSAIDs
Aspirin ->salicylic acid
What is a COX1 selective inhibitor
Aspirin
What are the non specific COX inhibitors
Flunixin
Phenylbutazone
Ketoprofen
What are the COX2 preferential inhibitors
Deracoxib
Carprofen
Meloxicam
What are the COX2 selective inhibitors
Firocoxib
Robenacoxib
T/F: NSAIDs can cross the BBB
T
Where does NSAID metabolism take place and how are NSAIDs excreted?
Liver
Urine and Biliary excretion (some NSAIDS have enterohepatic recirculation)
Antithrombotic effect of NSAID?
Inhibits thromboxane A2 -> no platelet aggregation
What are the antineoplastic effects of NSAIDs
COX2 is expressed by some cancers
Eg Transitional cell carcinoma
Osteoscarcoma
What NSAID is used often for its antineoplastic effects?
Piroxicam
What are the adverse effects of using NSAIDs
GI irritation/ ulceration -> prostaglandins maintain GI homeostasis
Renal damage and decreased blood flow -> PG control vasodilation –> decrease renal flow and papillary necrosis
Post operative analgesia and hypotension
Hepatotoxicity (acetaminophen metabolized to toxic intermediate)
What species is at a higher risk of renal damage from NSAIDs?
Cats
What drug is commonly used for colic/visceral pain in horses/cattle?
Flunixin Meglumine
What is the proper route of administration of Flunixin Meglumine
PO, IV, IM
Do NOT give IM to horse -> muscle necrosis
What species should you avoid using Flunixin Meglumine in due to its renal toxicity in
Birds
What drug is commonly used in horses to treat musculoskeletal pain
Phenylbutazone
What are the route of admin for Phenylbutazone
PO or IV
What is a washout period and when should you use one
Period, based on half life, that it takes for a drug to leave the system (usually 1-2wks)
Changing from steroid to NSAID
Changing from two different NSAIDs
What is the MOA of acetaminophen
Interferes with convertibility endoperoxides to PG and TX
When is acetaminophen used clinically?
Dogs -sometimes after neurological surgery
NEVER in cats
What are the toxic effects of Acetaminophen ?
Methemoglobinemia->MOST important
Hepatic necrosis
Hemolysis, icterus, anemia, Heinz bodies
Facial swelling, edema
What non-NSAID is an antagonist at prostaglandin E2 (PGE2) EP4 receptor
Grapiprant what
What is used to control neuropathic pain and prevent allodynia in dogs, cats, and horses
Gabapentin
Pre-emptively for acute pain or treat laminitis
What are the precautions to using Gabapentin
Sedation/ataxia ->dose dependent effects
Renally excreted-> caution in renal insufficiency
What is used to treat neuropathic pain or dorsal horn “windup” pain
Amantadine
Less common in small Amina’s
What is the MOA of Amantidine
Antiviral with NMDA receptor antagonist
Which of the following drugs is NOT a selective COX2 inhibitor ? A. Carprofen B. Phenylbutazone C. Robenacoxib D. Meloxicam
B. Phenylbutazone
What is the mechanism of action for the antithrombotic effects of aspirin
Irreversible thromboxane A2 inhibition
Binds to thromboxane receptor on platelet for the lifespan of the receptor (8-10days)
Why is IM injection of flunixin meglumine contraindicated in horses?
Risk of muscle necrosis
Do you use NSAIDs with glucocorticoids
NO! ARE YOU INSANE!?!?!?