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Neuro > Priniples Neuropharmacology > Flashcards

Priniples Neuropharmacology Flashcards

1
Q

How do blood vesselsi n the BBB differ to normal capillaries?

A
  • less fenestrations, pericytes, tight junctions, lots of mitochondria to facilitate active rtansport , layer of astrocytes as 2nd lineo f defence
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2
Q

Which drugs are most lipophilic and which are least on the S curve of lcoal brain uptake? Which drugs do not fit the trend?

A
  • natrium
  • morphine
  • heroin
  • nikotin
  • ethaanol
  • diazepam (most lipophilic, so most CNS specific)
    > Glucose and L-Dopa are not lipophilic but ae actively uptaen into the brain so present in n^ than expected concentrations
    > Phenobarbitol and phenytoin don’t get into the brain as much as they should for how lipophilic they are as PGP actively pumps out.
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3
Q

What is the role of PGP and what occours when it is over/under expressed?

A

mediates transembrane rtansport of lipophilic drugs

  • if overexpressed -> pharmacoresistant epilepsy (humans)
  • also over expressed at site of epileptic focus -> v AED concentration (antiepileptic drug)
  • under expressed in collies -> ivermectin sensitivity as cannot be pumped back out of cells
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4
Q

Define seizures

A
  • clinical sign (not disease)
  • transient and involuntary change in behaviour or neurological status d/t abnoral activity of populations of CNS neurons
  • hypersynchronous firing of neurons
  • seizures named following clinical signs
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5
Q

What is seen in association with epilepsy in dogs? humans?

A
  • dogs: behavioural probles eg. anxiety

- people: depression

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6
Q

When should seizure tx be initiated?

A
  • status epilepticus
  • cluster seizures
  • severe postictal signs
  • progessive (^severity or frequency)
    ? seizure/6months
    ? 2+ isolated seizures within 6 months
  • whatever owner will tolerate!
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7
Q

What is involved in client education regarding epilepsy?

A
  • life-time commitment
  • tx doesnt cure disease, just minimises signs
  • chart for seizure frequency (de-emotionalise the experience, objecify records)
  • rectal diazepam - give them something to do! ?efficacy as how much actually gets in?
  • side effects of drugs
  • 2/3 dogs respond to AED, some dont
  • epilepsy app from rvc
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8
Q

How should tx be started?

A
  • monotherapy (dont polypharm initially)
  • seizure freq influences choice of AED
  • monitor plasma levels of drug
  • ensure owner compliance!
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9
Q

Which drugs act on the excitatory nerve terminal?

A

> Carbamazine, phenytoin (see slide for others)
- presynaptic neuron use dependent Na channel: dampens excitation so only normal excitaion gets through.
- less effective than targetting GABA
Ketamine (see slide for others)
- postsynaptic neuron NMDA receptor
- good for refractory status epilepticus

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10
Q

Which drugs affect the inhibitory nerve terminal? How do their ctions differ?

A

> benzodiazepines
- need GABA so will not work if GABA depleted
- ^ frequency of chloride ion channel opening at GABAa- R
- ^ potency of GABA
- very rapid onset of action
phenobarbital
- ^ duration of chloride channel opening
- ^ efficacy of GABA
- can work with no GABA present if needed - bind different subunits to benzos
- slower onset of action ~20mins

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11
Q

When is phenobarb indicated?

A
  • sezing ~2hrs
  • refractory to diazepam
  • ALWAYS give diazepam first or at the same tiem as faster onset
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12
Q

Mode of action of phenobarbitone?

A

look up!!

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13
Q

Give a novel anti-epileptic drug. What is it’s mode of action?

A

partial agonist, modulates GABA channels
- 1000x less affinity than diazepam so can be stopped without dependance developing, and less opportunity for mis-use by owners

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14
Q

Outline dose, T1/2, therapeutic range and time to steady state of phenobarbital

A
  • 2.5mg/kg BID
  • 24-40hrs
  • 15-35ug/ml
  • 10-14d
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15
Q

How is Phenobarbital metabolised? Side effects?

A

liver

- sedation, PD, polyphagia, hepatotox (though should be ok if

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16
Q

Hhow regularly should you collect plasma levels when tx with phenobarbitone?

A
  • 14, 45, 90, 180 and 360d

- then q6m

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17
Q

What is the loading dose of Phenobarbital if indicated?

A

12-24mg/kg total dose within 24hrs

- equal dose q30mins - 4hrs to effect (ie. no seizures)

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18
Q

when and how can phenobarbitol doses be altered?

A
  • seizure freq equal or increased after 30
  • monitor drug leves
  • increment s of 5ug/ml
  • oral daily dose of mg PB = (desired conc/actual conc) x total mg PB per day [LOOK UP]
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19
Q

Side effects of phenobarbitol

A
  • TT4 and ft4 reduction
  • no efffect on ACTH stim
    > liver
  • ^ALP common
  • hepatotox with serum conc >35ug/ml
  • routine biochem +- BA stim q6-12 months may v elimination T1/2 with chronic use d/t cytochrome p450 system
    > rare but severe (idiosyncratic reactions)
  • behviour change
  • immune-mediated neutropenia, thrombocytonpenia and anaemia
  • superficial necrolytic dermatitis
  • hepatotoxic reactions (rapid ^ALT and abnormal BA)
  • ACTION :stop drug immediately and load with another AED (KBr)
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20
Q

Is KBr a first line tx?

A

Can be, or add on

21
Q

Dose, t1/2, tiem to steady state, therapeutic range, side effects and excretion of potassium bromide KBr?

A
  • 30-40mg/kg SID
  • 15-20d
  • 100-200d
  • 0.7-1.9mg/ml (2.3mg/ml?)
  • sedation, weakness, PU, PD, GI irritation and pancreatitis
  • renal
22
Q

How regularly are plasma levels needed for KBr tx?

A
  • 4 weeks, 8-12weeks

- then q6m

23
Q

Loading dose of KBr if indicated?

A

600mg/kg equal doses over 6d + mainainence dose

24
Q

What will be seen on biochem with KBr tx?

A

^ Cl as cannot distinguish from Br

25
Q

Why is the time to steady state so long with KBr?

A
  • Cl and Br recycled by body and rarely excreted
26
Q

Howo is KBr dose adjustment carried out?

A
  • full oral dose in mg/kg/day = (desired conc/actual conc) x current dose
27
Q

What dietary effects may be sen with KBr?

A
  • high chloride diet lowers serum conc
28
Q

What must you be aware of with KBr Tx? Action?

A
  • bromide toxicity (rare)
  • severe ataxia, sedation, somnolence, skin reactions
  • eg. dogs with renal insufficiency (v elimination)
    > Action: iv saline to enhance renal excretion
29
Q

When is imepitoin indicated?

A
  • onsider 1st line tx for newy diagnosed idiopathic epilepsy (mild)
  • good side effect profile so tx can be considered earlier for less severe epilepsy
  • dogs with severe side effects on phenobarbitone or other anticonvulsants
  • unsatisfactory seizure contol on phenobarb or other anticonvulsants
  • NOT indicated ith acute (cluster or status epilepticus) seizures and NOT FOR CATS
30
Q

Dose, T1/2, time to steady state, therapeutic range, side effects and metabolism of impitoin?

A
  • 10-30mg/kg BID
  • 2hrs
  • 1-2d
  • N/A
  • sedation, polyphagia, hyperactivity
  • liver
31
Q

How regularly are plasma levels needed with Imepitoin?

A

N/A

32
Q

Reasons for epilepsy tx failure?

A
  • incorrect dx (MRI?)
  • incorrect choice of AED
  • incorrect dosage/low AED levels
  • newly developed dz (liver/kidney/pancreatic dz)
  • change in patent weight
  • patient tolerance to drug (PB/benzos)
  • monotherapy is insufficent
  • refractory seizures
  • pooor compliance
33
Q

How can tx failure be overcome?

A
  • monitor and adjust drug dose
  • monitor drug levels
  • add anticonvulsant
  • consider new drug
34
Q

How is refracory epilepsy defined?

A
  • seizre frequency reduction of less than 50%
35
Q

How many dogs will be refractory to both PB and KBr combination?

A

20-330%

36
Q

Give egs of add on drugs fo refractory seizures

A
  • gabapentin
  • pregabalin
  • levetiriracetam
  • zonisamide
  • felbamate
37
Q

First choice of AED in CATS? Dose, t1/2, time to steady state, therapeutic range and side effects?

A
  • 2-3mg/kgOP SID/BID
  • 3-43hrs
  • 10-14d
  • 10-30.2ug/ml
  • polyphagia, bone marrow suppression, cutaneous hypersensitivities
  • does NOT induce liver enzymes as much as dogs
38
Q

2nd choice AED for cats? t1/2, dose and side effects?

A

> Diazepam

  • 15-20hrs (6x longer than in dogs!!)
  • 5-10mg PO BID/ID
  • acute fulminant hepatotoxicosis
39
Q

What should be monitored with diazepam in cats?

A
  • evaluation liver enzymes 5-7d after initiation
40
Q

Which other AED may be used in cats?

A
  • levatiracetam (dose 10-20mg/kg PO TID, t1/2 5.3hrs)

- gabapentin (dose 5-10mg/kg TID)

41
Q

What are the consequences of status epilepticus?

A 
> Seizure up to 30mins 
- high symp tone
- arterial hypertension
- ^ cerebral blood flow 
- hypoxaemia
- hypercarbaemia
- hyperglycaemia
- lactic acidosis 
> seizure >30mins
- continuous muscle contraction 
- hyperthermia
- acidosis
- myolysis (myoglobinuria, hyperkalaemia: renal failure) 
- hypoglycaemia (energy depletion) 
- hypotension
- cardiac arrythmias
42
Q

What effects may treatment following seizure have?

A
  • v HR
  • v R
  • v BP
    combined with seizure -> hypoxia and hypotension
43
Q

How can hypoxia and hypotension, hyperthermia be treated?

A
  • oxygen
  • fluids
  • cool down
43
Q

How can pathologic effects of seizures be classified?

A

1* and 2* effects (complications)

44
Q

What can the ultimate result of status epilepticus be?

A

energy depletion, circulatory collapse and organ hypoperfusion -> multiple organ failure

45
Q

3 goals of tx of status epilepticus

A
  1. stop the seizures
  2. protect the brain
  3. think about the future
46
Q

Which drugs are indicated for use in status epilepticus lasting 120mins??

A

5-30mins: Diazepam, Midazolam
30-60mins: Phenobarbitol, KBr
60-120mins: Levetiracotam, propofol anaesthesia
120min+: Ketamine anaesthesia, iso- or sevoflurane anaesthesia, Pentobarbital, Phenobarbital and KBr

47
Q

How can 2* complications of status epilepticus be minimised

A 
> monitor
- HR
- BP
- O2
- electrolyte/fluid ballance 
- body temp 
> minimise brain injury
- tx hypotension (volume expansion, fluid balance) 
- tx hypoxaemia (O2 upplementation) 
- minimise hyperthermia 
- minimise renal impairment
48
Q

What must be addressed when looking at status epilepticus?

A

Dx and Tx udnerlying disease

  • hypoglycaemia/electrolyte imbalance (correct)
  • possible toxicity (diuresis and decontamination)
  • intracranial cause (imaging, CSF analysis)
  • referral

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