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Part 3 – PM3B COPY T > (PM3B) CNS Drug Delivery > Flashcards

(PM3B) CNS Drug Delivery Flashcards

1
Q

What are the compartments of the brain?

A

(1) Blood
(2) Cerebrospinal fluid
(3) Brain

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2
Q

Where is cerebrospinal fluid held?

A

(1) Ventricles

(2) Subarachnoid + intrathecal spaces

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3
Q

What is the volume of the cerebrospinal fluid?

A

140mL

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4
Q

What is the rate of production of cerebrospinal fluid?

A

35 mL/hr

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5
Q

At what rate does blood flow through the brain?

A

60 L/hr

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6
Q

What barrier is between the brain and the blood?

A

Blood brain barrier

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7
Q

What barrier is between the blood and the cerebrospinal fluid?

A

(1) Arachnoid villi

(2) Chloroid plexus

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8
Q

What barrier is between the cerebrospinal fluid and the brain?

A

Ependyma

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9
Q

What is the blood brain barrier?

A

Tight junctions between cells

Blocks diffusion of polar solutes

Limited paracellular pathways

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10
Q

How is the blood brain barrier selective?

A

Brain capillaries have restricted permeability compared to peripheral capillaries

Permeability restricted to <600Da (small molecules) + lipophilic substances

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11
Q

How do cells in the brain get solutes?

A

(1) Small lipophilic drugs diffuse freely

(2) Carrier-mediates transport of glucose/ amino acids/ proteins from high to low concentration

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12
Q

What are efflux pumps?

A

Transporters

Responsible for extruding drugs from brain

ATP-binding cassette transporter P-gp + multidrug resistant protein are key principles of efflux mechanism

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13
Q

What are some strategies for CNS drug delivery?

A

(1) Between tight junctions of BBB
(2) Through BBB –enhancement of transport across the endothelium
(3) Around the BBB – direct intracranial drug delivery

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14
Q

What is intracarotid drug delivery?

A

Injection directly into carotid artery

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15
Q

What is the role of osmotic agents in CNS drug delivery?

A

Strategy to cross BBB

Usually hypertonic mannitol

(1) 25% solution infused into carotid artery over 30 seconds
(2) Injection of drug through same cannula it can freely diffuse into the CNS

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16
Q

How does mannitol increase blood brain barrier permeability (mechanism of action)?

A

(1) Hypertonic solution thought to osmotically pull water out of endothelial cells – causes cell shrinkage
(2) Cause disengagement of extracellular domains of proteins forming the tight BBB junctions

17
Q

What is the purpose of disruption of blood brain barrier via penetration enhancers?

A

Strategy to cross BBB

(1) Surfactant molecules disrupt BBB by acting with phosphatidylcholine head groups
e. g. ethanol surfactants: SDS/ glycerol/ polysorbate-80

18
Q

What are some potential issues with disruption of blood brain barrier via penetration enhancers?

A

Toxicity issues

(1) Neuronal damage
(2) Infarction
(3) Learning impairment
(4) Gliosis – scars in CNS

19
Q

What is the purpose of the use of prodrugs at the blood brain barrier?

A

Strategy to cross the BBB

(1) DP-VPA is designed to penetrate CNS intact
(2) Release VPA through hydrolytic activity of phospholipase A2

In testing – phase 2 trials have begun

20
Q

What are some potential benefits of combining drugs and pumps for brain/ CNS delivery?

A

(1) Significantly lower dose – fewer side effects
(2) Target effectiveness – avoiding 1st pass metabolism
(3) Improved adherence – overcomes inability to take medication
(4) Additional drug options –targeted nature of delivery allows for more drug candidates

21
Q

What is intracerebral (intraparenchymal) delivery?

A

Drug delivery directly into parenchymal space in brain

(1) Can be injected directly by intrathecal catheters
(2) via controlled-release matrices
(3) via microencapsulated chemicals
(4) via recombinant cells

22
Q

Why is a high local dose required for intracerebral (intraparenchymal) delivery?

A

To drive convection enhanced diffusion (CED)

Drives drugs to larger tissue regions

23
Q

What are intracerebral devices?

A

Implants made of either biodegradable/ non-biodegradable polymeric materials

Encapsulate drugs within them

e.g. Ommaya reservoir

Used to deliver chemotherapy

24
Q

What are Ommaya reservoirs?

A

Intracerebal devices

Used to deliver chemotherapy

Contain etoposide (anti tumour agent)

Treatment of metastatic brain tumour

25
Q

Give an example of an osmotic implant.

A

DUROS

26
Q

What is DUROS?

A

Osmotic implant

Delivers drug for 3-12 months

Precise zero order delivery kinetics

27
Q

What is a GLIADEL wafer?

A

Polymer depot

Approved for brain-tumour therapy

Contains carmustine

28
Q

What is inrtaventricular delivery?

A

Transcranial drug delivery

Bypasses BBB

Injection directly into cerebral ventricle

Best suited for meningioma treatment + metastatic cells of cerebrospinal fluid

Distributes drugs mainly into ventricles + subarachnoidal area of the brain

29
Q

Give an advantage of intraventricular delivery.

A

Lack of interconnection with interstitial fluid of brain – unlike intracerebal delivery

Achieves higher concentration in the brain

30
Q

Give a disadvantage of intraventricular delivery.

A

Chance of causing subependymal astrogliatic reaction

- Due to high drug exposure at ependymal surface of brain

31
Q

What is DepoCyt?

A

Liposomal sustained-release formulation

Contains cytarabine

Direct administration into cerebrospinal fluid

32
Q

Give an advantage of using DepoCyt.

A

(1) Half-life of 5.9-82.4hrs compared to just 10 minutes

(2) Systemic exposure is low following intrathecal administration

33
Q

What is intrathecal drug delivery?

A

Direct administration of drugs through intrathecal route into cisterna magna of brain

34
Q

What is ITB?

A

Intrathecal baclofen

Treatment of spasticity

35
Q

Give an advantage of intrathecal delivery.

A

Less invasive than intraventricular

36
Q

Give a disadvantage of intrathecal delivery.

A

Chance of drug spreading along distal space of spinal canal

37
Q

What are some types of non-opioid drugs used for treatment of chronic pain via the spinal route?

A

(1) Local anaesthetics
(2) Adrenergic agonists
(3) NMDA antagonists
(4) Others – e.g. aspirin/ baclofen/ gabapentin

Part 3 – PM3B COPY T (33 decks)

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