neuro pharm Flashcards
mechanism of action of local anesthetics
blockage of voltage dependent sodium channels, reduces influx Na ions, prevents depolarization and conduction of action potential
-3 nodes of ranvier blocked for good effect
factors that affect the local anesthesia
- Ph/pKa: affects ionization of drug, which affects action of drug (eg. in infection, pH is lowered so there is more charged drug–which can’t cross into cells)
- lipid solubility–affects potency
- protein binding–affects duration of action (inc. protein binding inc. duration of action)
- vasoconstriction–affects duration and potency (slows blood flow and prevents removal of anesthetic from region)
factors that determine the susceptibility of nerve fibers to blockade of local anesthetics
- smaller fibers are blocked more easily
- myelinated nerves are blocked more easily (only have to block nodes of ranvier)
- peripheral fibers blocked sooner than core (exposed to more drug
- temporal progression: autonomic lost first, then sensory, then motor
major toxic effects of local anesthetics
Neuro/CNS:
- mlid: excitability, slurred speech, face twitching, nystagmus, loss consciousness, disorientation
- severe: tonic-clonic seizure, generalized CNS depression
Cardio:
- mild: hypertension, tachycardia
- severe: hypotension, bradycardia, bradypnea, cardiac arrest
Other: sweating, metallic taste, tinnitus
bupivicaine toxicity:
severe cardiotoxicity (hypotension, arrhythmias) no treatment of overdose
cocaine toxicity
severe HTN, cerebral hemorrhage, MI
amide local anesthetics
used IV bupivicaine, ropivicaine (long duration) lidocaine (medium duration) prilocaine, etidocaine metabolized in liver (liver dyfx inc. half-life)
ester local anesthetics
used topically -long duration: tetracaine -medium duration: cocaine -short duration: procaine -surface active: **benzocaine, cocaine metabolized by psueocholinesterases in plasma
ester local anesthetic toxicities
allergic reaction
local anesthetics +/- vasoconstrictor (epineprhine)
- *Cocaine does not require administration of vasoconstrictor since it has intrinsic sympathomimetic activity (all over LA are vasodilators)
- when adding vasoconstriction to LA–>enhances duration of action (but does not make it work faster)
- don’t use in end-organ surgery (tips of fingers, ears, nose) can cause ischemia
therapeutic uses of local anesthetics
-anesthesia of mucous membranes (optho-tetracaine (ester))
-topical application before needle stick (lidocaine, prilocaine)
-regional nerve block anesthesia (patient to sick for general anesthesia)
-spinal anesthesia (shorter acting)
-epidural anesthesia (longer acting)
benefts are no systemic effects!
half-life of anti-epileptic drugs
- pts need 24hr coverage
- drugs with half life <6h but works with BID dosing
AED drug levels and toxicity
- toxicity is always determined by patient symptoms not byt drug levels
- phenytoin and valproate are highly protein bound
which AED are renally cleared?
- gabapentin, pregabalin, levetiracetam and oxcarbazepine-active metabolite are excreted renally
- dec. dose in renal failure
clearance of topiramate:
2/3 kidney and 1/3 liver
which AEDs induce CYP450 enzymes?
phenytoin, carbamazepine, barbituates are potent inducers
- induce metabolism of other drugs–esp. oral contraceptive (dec. effectiveness)
- carbamazepine auto-induces it’s own metabolism
which AEDs are inhibitors of CYP450 enzymes?
-valproate (raises levels of CYP450 metabolized drugs)
which AED has non-linear kinetics?
phenytoin
- metabolizing enzymes saturate
- raising dose higher can result in exponential increases in serum drug levels
Which AEDs can be given IV and used for status epilepticus?
o Fos-phenytoin (requires high loading dose in this setting)
o Barbiturates (requires high loading dose in this setting)
o Lacosamide
o Valproate
o Benzodiazepines
o Levetiracetam
treatment prognosis for patients with idiopathic generalized epilepsy
good, vast majority can be made seizure-free with drugs
treatment prognosis for patients with symptomatic generalized epilepsy
rarely controllable
goal is to reduce number of grand-mal seizures and atonic seizures
treatment prognosis for patients with focal epilepsy?
- 65% can be made seizure free with drugs
- if focal epilepsy doesn’t respond to first 2-3 drugs tried it won’t respond at all
- non-responsive may be candidates for resective epilepsy surgery (most commonly performed surgery is anterior temporal lobectomy for mesial temporal lobe epilepsy)
AEDs that work on GABAergic system
Benzodiazepines (midazolam, lorazepam, diazepam, clonazepam)
- barbituates (phenobarbitol, pentobartbitol, primidone)
- gabapentins (gabapentin, pregabalin)
AEDs that work as Na-channel blockers
- Phenytoins (phenytoin, fos-phenytoin)
- carbamazepine (carbamazepine, oxcarbazepine)
- lamotrigine
- lacosamide
AEDs that work as T-type Ca channel blockers
Ethosuximide
AEDs that work for every type of seizure
o Benzodiazepines
o Valproate
o Lamotrigine
o Zonisamide
AEDs that work on generalized tonic-clonic seizures
all except euthosixumide (absence seizures) and lacosamide (focal sz)
AEDs for focal seizures
o All except for ethosuximide (which only treats absence seizures)
AEDs for absence seizures
o Ethosuximide
o Benzodiazepines, Valproate, Lamotrigine, Zonisamide
AEDs for myoclonic sz
o Topiramate
o Levetiracetam
o Benzodiazepines, Valproate, Lamotrigine, Zonisamide
AEDs for atonic seizures
o Topiramate
o Benzodiazepines, Valproate, Lamotrigine, Zonisamide
benzodiazepines
MOA
specific drugs and indications
-MOA:Bind to an allosteric modulation site on the GABAA receptor, which is coupled to a Cl- channel → Cl- opens more frequently → hyperpolarization → inhibition
- Midazolam: status epilepticus (IV)
- lorazepam/diazepam: #1 for acute sz
- clonazepam: myoclonic sz
Lose effect and have significant potential for addiction when given chronically
Flumazenil: competitive antagonist at benzodiazepine receptor (can cause sz in patients taking benzos)
barbituates
MOA
toxicities
MOA: Bind to an allosteric modulation site on the GABAA receptor (different from benzodiazepines) → Cl- remains open for longer → hyperpolarization → inhibition
toxicities: respiratory depression (when used IV), sedation, depression, cognitive impairment, hepatotoxicity and allergic rash; NOT first line drugs
- phenobarbitol: acute or chronic sz
- pentobarbital: refractory status epilepticus
- primidone: GTC, focal sz, essential tremor
gabapentins
MOA:
specific agents
MOA: Binds to the α2δ subunit of presynaptic Ca2+ channel → leads to modest reduction in release of several neurotransmitters (including substance P)
gabapentin: focal sz *dose limited by gastric absorption; few side effects
pregabalin: neuropathic pain is main use; side effects are sedation and wt gain; more potent
Phenytoins
MOA
toxicities
specific agents
MOA: Voltage and frequency-dependent block of Na+ channels (if cell is depolarized and firing at high frequencies) → prevents high frequency firing, allows normal frequency firing
- NOT useful for types of seizures other than generalized tonic-clonic (GTC) or focal seizures
- Acute side effects include sedation, ataxia, dizziness and diplopia
- Chronic side effects include gingival hyperplasia, hirsutism, acne, coarsening of facial features and osteomalacia (induces metabolism of vitamin D by CYP450)
- Dangerous side effects include SLE-like syndrome, hepatotoxicity, myelosuppression
- Many drug interactions (because of induction of CYP450 enzymes and high protein-bound state)
-phenytoin and fos-phenytoin: GTC and focal seizures
carbamazepine
MOA:
toxicities
MOA: Voltage and frequency-dependent block of Na+ channels (if cell is depolarized and firing at high frequencies) → prevents high frequency firing, allows normal frequency firing
toxicities:
- Can worsen absence, atonic and myoclonic seizures
- Acute side effects include ataxia, dizziness, diplopia, sedation, but NONE of the cosmetic effect associated with phenytoin (e.g. acne, hirsutism)
- Chronic side effects include hyponatremia and leukopenia (not too big of a deal)
- Serious side effects include rash and aplastic anemia
- Many drug interactions (because of induction of CYP450 enzymes)
Uses: partial sz, GTC
- carbamazepine: more toxicity; autoinduces it’s own metabolism
- oxocarbazepine: hyponatremia is more common
lamotrigine
MOA:
toxicities
uses
MOA: Voltage and frequency-dependent block of Na+ channels (if cell is depolarized and firing at high frequencies) → prevents high frequency firing, allows normal frequency firing
Toxicities:
- Very well tolerated
- Most common side effects are insomnia and headaches
- Dangerous side effects include Stevens Johnson syndrome and other rashes (prevented by titrating the drug extremely slowly)
- Very few drug interactions and probably NOT teratogenic (so safe to give to pregnant epileptics)
Uses: all types of sz
lacosamide
MOA
toxicities
Uses
MOA: Enhances SLOW inactivation of Na+ channels, through a different molecular mechanism than lamotrigine, carbamazepine or phenytoin
- Toxicities: dizziness when combined with other NA channel blockers
- used for focal sz
ehthosuximide
MOA
Use
toxicities
MOA: Voltage-dependent block of “transient” T-type Ca2+ channels in the thalamus → blocks abnormal thalamic excitability → stops 3 Hz spike-and-wave activity in cortex
Use: only works on absence sz
Toxicities:
- Mild side effects include sedation, dizziness, cognitive impairment, headache and behavioral changes
- Severe side effects include Stevens Johnson syndrome and myelosuppression
valproate
MOA
Use
Toxicities
MOA: Has ethosuximide effects on T-type Ca2+ channels, increases brain GABA levels and may have phenytoin-like effects on Na+ channels
Uses: all types of sz
toxicities:
- Contraindicated during pregnancy (neural tube defects)
- Very bothersome triad of side effects includes weight gain, hair loss, tremor
- Mild side effects include GI upset, sedation, cognitive problems
- Severe side effects include hepatic failure (infants), pancreatitis, thrombocytopenia and hyperammonemia
- Can rarely cause a reversible form of polycystic ovary syndrome
topiramate
MOA
Use
toxicity
MOA: Inhibits voltage-sensitive Ca2+ channels and Na+ channels, has benzodiazepine-like effects on GABA-induced Cl- currents, inhibits carbonic anhydrase and Glu-receptors
Use: all sz except absence
toxicities:
- Very safe drug with few drug interactions
- Milder side effects include sedation, paresthesias, cognitive impairment (especially aphasia), weight loss
- More notable effect is kidney stones (1% of patients due to inhibition of carbonic anhydrase)
zonisamide
MOA
Use
toxicities
MOA; Phenytoin-like effect on Na+-channels, ethosuximide-like effect on T-type Ca2+ channels, inhibits carbonic anhydrase
Use: all sz types
toxicities:
- NO drug interactions
- Milder side effects include sedation, dizziness, cognitive impairment, decreased appetite, weight loss
- More severe side effects include rashes, kidney stones (1% of patients due to inhibition of carbonic anhydrase)
- Extremely rare side effects include agranulocytosis, oligohydrosis with hyperthermia
levetiracem
MOA
Use
Other
MOA: Binds very strongly and specifically to the synaptic vesicle protein SV2A (but the precise mechanism of action is not yet known)
Use: partial sz, myoclonic sz
Notes:
- Faster onset then most antiepileptic drugs
- Appears completely safe (so far)
- Mild side effects include sedation, irritability and psychosis (1%)
Which drugs could I use to treat a productive cough? MOA? AE?
expectorant: guaifenesin
MOA-Increase secretion of mucus and thin out mucus→facilitates upward expulsion of sputum
AE-GI (N/V, irritation to gastric mucosa)
which drugs could I use to treat a nonproductive cough?
central acting-Codeine/hydrocone
central acting-dextromethorphan (promethazine)
peripheral acting-benzonatate
which drug could I use to treat a patient with thick bronchial secretions due to cystic fibrosis? MOA? AE?
Mucolytic: N-acteylcysteine (delivered by nebulizer or directly w/ bronchoscope)
Breakdown of mucopolysaccharides in bronchial secretions to smaller components
smells and tastes bad
what demulcents?
Sticky substances that protect lining of respiratory tract from irritation
Codeine–MOA, Uses, AE
-MOA: reduce excitability of the cough center in the medulla
AE: respiratory depression (worse in small kids, pts w/ COPD, head injury, inc. intracranial pressure), constipation, miosis, sedation/drowsiness, addiction potential
-used in non-productive cough
dextromethorphan (promethazine)–MOA, Uses, AE
- MOA: : reduce excitability of the cough center in the medulla
- Uses: non-productive cough
- AE: fewer side effects than codeine! (At high doses—confusion, excitation, nervousness, irritability, nausea, dizziness, cardiac arrhythmias, respiratory depression)
benzonatate–MOA, uses, AE
- MOA: local anesthetic affect on stretch receptors in respiratory passages→reduces afferet input to cough center
- Uses: non-productive cough
- AE: hypersensitivity (bronchospasm, laryngospasm, CV collapse; contraindicated in allergic to procaine/tetracaine
Which drugs can be used to treat cytotoxic drug induced emesis? Which ones are most effective?
most effective: 5-HT3 receptor antagonists (odansetron), centrally acting dopamine receptor antagonists (metoclopramide)
- neurokinin receptor antagonist (aprepitant): delayed vomiting
- also cannabinoid receptor antagonist (dronabinol)
Which drugs can be used to treat motion sickness?
muscarinic receptor antagonists (scopolamine)
histamine-1 receptor antagonist (meclizine)
Which anti-emetics are dopamine antagonists? What is the MOA? What are the AEs?
- chlorpromazine
- prochlorperazine
- thiethylperazine
- droperidol
MOA: Depress excitability of CTZ by blocking dopamine (D2) receptors and transmission
AE:
- Sedation
- Extrapyramidal sx: dystonia, torticollis, oculogyric crises, akathisia, gait disturbances
- allergic