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Neuro Pharmacology

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Which type of chronic pain is characterized by a poor correlation between tissue pathology and pain?
Chronic Non-Cancer Pain
What type of pain is usually cutaneous or superficial?
Somatic
What type of pain is deep, dull, and poorly localized?
Visceral
What is the quality of neuropathic pain?
Burning or dysesthetic
Neuropathic pain results from damage to what?
A peripheral nerve
Where do fast and slow pain fibers synapse?
On second-order neurons in the dorsal horn of the spinal cord
Where do 2nd order pain neurons in the spinal cord project?
Medulla and/or thalamus
What is the basic mechanism of local anesthetics?
Blockade of voltage-gated Na⁺ channels
What are the two important features common to both amide and ester forms of local anesthetics?
1. Hyprophilic amine and hypdrophobic aromatic moiety
2. The amine can be protonated, with pKa of 7.5-9.0
Which form of a local anesthetic, the charged or uncharged, is more membrane-permeable?
The uncharged
Which form of a local anesthetic, the charged or uncharged, is a better blocker?
The charged
What is the function and significance, in terms of local anesthetics, of the selectivity filter on a voltage-gated Na⁺ channel?
It allows entry of only Na⁺, H₂O, and H⁺ into the channel
The anesthetic molecules must diffuse through the cell membrane and reach their binding sites from inside the cell
True of False: Only the charged forms of local anesthetics can bind their receptor sites inside the Na⁺ channel.
False
(charged binds better than free base, but free base can still bind)
Which pain fibers are blocked at lower concentrations of local anesthetics?
Small, unmyelinated (C fibers)
Which type of nerve fibers (touch, pain, temperature, motor, proprioception, etc) are blocked at the highest concentrations (i.e. last)?
Touch, motor, proprioception (Aδ)
What effect does inflamed tissue have on the local anesthetics?
⬢ Inflamed tissue has lower extracellular pH
⬢ More drug is protonated (extracellular), so membrane diffusion is inhibited
⬢ Block of inflamed tissue is slower than normal
How are local anesthetics generally marketed/formulated?
As hydrochloride salts
Why does injection of local anesthetic hydrochloride solutions "sting"?
Because of the acidity of the solutions
How much unchanged local anesthetic is found in urine?
Very little, if any
How are ester LAs and amide LAs metabolized?
Ester LAs = hydrolysis by plasma ChE
Amide LAs = hydrolysis by liver microsomal esterase
Which type of local anesthetics is rapidly degraded in blood by plasma cholinesterases?
Ester LAs
What are the cardiovascular effects of cocaine?
Blocks NE uptake (vasoconstriction and HTN)
Increased HR
What is the relationship between blood solubility and induction rate for general inhaled anesthetics?
Inverse
Which inhaled anesthetic will have a faster rise in arterial tension, one with a low blood/gas partition coefficient (B/G) or one with a high B/G?
Low (poorly soluble)
What effect can mechanical hyperventilation have on in inhaled anesthetics?
It can increase the rate of anesthesia onset
Does pulmonary blood flow rate have a direct or inverse relationship with induction rate?
Inverse
What effect will heart failure have on the administration of inhaled anesthetics?
It will increase the rate of induction
What drug should be administered with extreme caution with halothane only (is OK with other inhaled anesthetics) and why?
Epinephrine
Halothane uniquely sensitizes myocardium to dysrhythmias induced by catecholamines
What is the major route of elimination for inhaled anesthetics?
Exhalation
For which inhaled anesthetic is liver metabolism a significant process and important consideration due to the risk of severe hepatitis post-anesthesia?
Halothane
For which inhaled anesthetic is liver and renal metabolism a significant process and important consideration due to the risk of nephrotoxicity?
Methoxyflurane
(metabolism releases fluoride ions)
What type of toxicity is a unique risk of Nâ‚‚O and why?
Hematotoxicity
Nâ‚‚O oxidizes B12
Which inhaled anesthetic can cause malignant hyperthermia and what is the treatment should this develop?
Halothane
Dantrolene
Why can Nâ‚‚O not be used alone as an inhaled anesthetic?
100% N₂O ≠ 1.0 MAC
What three barbiturates are often coadministered with inhaled anesthetics and what is their benefit?
Thiopental
Methohexital
Thiamylal

Ultra-short acting - unconsciousness in ~30 seconds
What is the advantage of propofol over barbiturates?
Recovery is even faster
What is a risk with propofol that limits its use in some situations?
Marked drop in systemic blood pressure
What drug can be administered with inhaled anesthetics instead of propofol in patients with cardivascular disease?
Etomidate
What drug is valued in general anesthesia because it causes anterograde amnesia?
Benzodiazepines (Midaxolam)
What two factors limit the use of ketamine?
1. Cardiovascular stimulant actions (but helps with pts in cardiovascular shock)
2. Postoperative psychomimetic reactions (give with a benzodiazepine)
What is the state induced by ketamine?
Dissociative amnesia
(sedation, analgesia, amnesia, disconnection from surroundings)
What is the mechanism of action of ketamine?
NMDA blockade
What are the primary analgesics used during anesthesia?
Opioids
Which opioid carries an FDA block box warning and for what?
Droperidol
Prolongation of QTc interval, leading to cardiac arrhythmias
What is the general (not molecular) mechanism of inhaled anesthetics?
Disruption of normal neuronal function by increased inhibitory and decreased excitatory synaptic transmission
What is the gold-standard treatment for Parkinson's disease?
Levodopa
Why does levodopa lose its efficacy over time?
Because of continued neurodegeneration (loss of synapses)
Why do other drugs still work once levodopa is no longer beneficial in treating a patient with Parkinson's Disease?
Because the dopamine receptors are still present and can be activated directly
What symptom is the result of an excess of levodopa?
Dyskinesia
Are anti-muscarinics useful in the treatment of Parkinson's disease?
No
What is entacapone?
COMT inhibitor
(used with levodopa in treatment of PD)
What is carbidopa?
Decarboxylase inhibitor
(used with levodopa in treatment of PD)
Selective dopamine agonists used in the treatment of Parkinson's Disease target which dopamine receptors?
Dâ‚‚-like Dopamine Receptors
(D₂, D₃, and D₄)
In most cases, antiphsychotic selections are made based on what?
Side effect profile
Dystonic reaction responds rapidly to what treatment?
Anticholinergic drugs (IM or IV)
What drugs work to treat APD-induced parkinsonism?
Antimuscarinics
Akathisia resulting from APDs can be treated how?
Change of dose, drug, anti-EPS drugs
Propanolol
Lorazepam
What is the nature of the relationship between the log dose and log affinity of the typical antipsychotics?
Linear
What is the treatment for tardive dyskinesia caused by typical antipsychotics?
Sometimes responds to change of dose/medication
(Often acutely worsens with dose reduction)
What is the treatment for neuroleptic malignant syndrome caused by typical antipsychotics?
Stop APD and Hospitalize
What are the acute side effects of typical antipsychotic drugs? (4)
1. Sedation (due to histamine receptor blockade)
2. Anticholinergic (low potency = greater side-effct)
3. Orthostatic hypotension (due to α1-adrenergic blockade)
4. EPS
What are the side effects due to ACh blockade by typical antipsychotics?
Dry mouth
Constipation
Urinary retention
Blurry vision
Tachycardia
Do low potency typical antipsychotics have a greater or lesser degree of side effects than high potency ones in regards to:
1. Sedation/anticholinergic
2. Hypotension (alpha-1 blockade)
3. EPS
1. Sedation/Anti-Cholinergic = Greater (potency inversely related)
2. Hypotension = Greater (potency inversly related)
3. EPS = Lesser (potency directly related)
Is thioridazine a high, low, or medium potency typical antipsychotic?
Low
Is perphenazine a high, low, or medium potency typical antipsychotic?
Medium
Is haloperidol a high, low, or medium potency typical antipsychotic?
High
Which 5-HT receptor, in particular, do atypical antipsychotics have a high affinity for?
5-HT2A
What two things do clozapine carry a special FDA approval for?
1. Tretment resistant patients
2. Reducing risk of suicide in schizophrenia and schizoaffective disorder
Which two antipsychotics have the greatest effect on QTc?
Thioridazine
Ziprasidone
For which patients should two AEDs be considered?
Those that have failed different AEDs as monotherapy
What are the four primary/general mechanisms of AEDs?
1. Block Na currents
2. Enhance GABA-mediated Cl currents
3. Block T-calcium currents
4. Block glutamate-mediated currents
What is the rate limiting step in the production of eicosanoids?
Release of AA by phospholipase A2
What is the cellular location and activation state of COX?
Intracellular membrane-bound enzyme
Constitutively active
What is the cellular location and activation state of lipoxygenases?
Soluble cytoplasmic enzymes
Migrate to cell membrane upon cell activation
What effect do leukotrienes have on inflammation?
Monocyte and granulocyte chemotaxis
What are the effects of prostaglandins and leukotrienes on clotting?
Thromboxanes activate platelets
Prostacyclins oppose clotting of platelets
Which AA derivatives constrict airway smooth muscle?
Cysteinyl LTs
Where are COX2 enzymes found?
Inflammatory cells such as macrophages
How do NSAIDS exert their antipyretic effect?
By blocking hypothalamic prostaglandin production

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