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Pharmaceutics II Exam 2 > Part 4 - Transdermal Drug Delivery Systems > Flashcards

Part 4 - Transdermal Drug Delivery Systems Flashcards

1
Q

there are many different dosage forms available via the skin route.
name those that give SYSTEMIC effects and those that give LOCAL effects

A

systemic effects - transdermal patch

local- ointments, creams, lotions, topical solutions, pastes, liniments, powders, gels, tinctures, aerosols

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2
Q

what is percutaneous absorption?

A

the absorption of substances from outside the skin to positions beneath the skin (including entrance to the bloodstream)

remember: per in Latin means THROUGH

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3
Q

give the components of the stratum corneum of the skin

A

protein, water, lipid

40% protein (keratin)
40% water
20% lipid (triglycerides, free fatty acids, cholesterol, phospholipids)

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4
Q

name the types of skin penetration that can occur with a drug

A

-transcellular penetration
-intercellular penetration
-transappendageal penetration

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5
Q

differentiate between the types of skin penetration by a drug

A

transcellular = across cells. PASSIVE. no enzymes needed

intercellular - between cells. again - no energy or enzymes needed

transappendageal - penetration via hair follicles, sweat/sebum glands, and pilosebaceous apparatus

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6
Q

between the 3 types of skin penetration by a drug, which is the most common absorption mechanism?

A

intercellular penetration

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7
Q

paracellular penetration is also known as….

A

intercellular penetration

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8
Q

put the following in order from superficial to deep:

dermis
stratum corneum
epidermis

A

statrum corneum
epidermis
dermis

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9
Q

of the 3 penetration mechanisms, which does not happen naturally?

A

transappendageal penetration.
physically pushed through a hole (hair follicle, sweat/sebum gland, pilosebaceuos apparatus)

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10
Q

name 5 factors that affect percutaneous absorption

A

-drug
-area of application
-physiochemical attraction to the skin compared to the vehicle
-hydration of the skin
-medicated application period

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11
Q

explain how the drug itself is a factor that affects percutaneous absorption

A

the concentration – high concentration will mean fast absorption (Fick’s law)

liphophilic drugs penetrate better

ionization reduces penetration (PKA IS IMPORTANT)

small molecules (100-800MW) penetrate faster

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12
Q

for a transdermal patch, what is the ideal molecular weight for the drug? why?

A

400

MW 100-800 can penetrate

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13
Q

true or false

hydrophilic drugs undergo faster percutaneous absorption

A

FALSE - lipophilic

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14
Q

Explain how pka value of a drug affects percutaneous absorption

A

ionization will reduce penetration. therefore, we want to control the pH so the drug remains unionized

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15
Q

what is the thinnest area to apply a transdermal patch and thus has the quickest sbsorption

A

skin behind the ear

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16
Q

explain how the area of application of the drug on the skin is useful

A

can help to control the dose.

normally, all patches are the same dose. therefore, to increase the dose you would increase the area of application by applying 2 patches instead of 1

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17
Q

non polar or polar:

which drug will go the transcellular route? what about intercellular?

A

nonpolar drugs will go the transcellular route (if small)
and polar drugs will go the intercellular route
(unionized, but has polar functional groups)

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18
Q

what is the ideal partition coefficient for percutaneous absorption

A

1
good for solubility and for permeability

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19
Q

what kind of drug will go through the transcellular pathway of percutaneous absorption

A

only drugs that are lipophilic and small

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20
Q

true or false

all percutaneous absorption mechanisms are passive

A

FALSE - transcellular and intercellular are, but not transappendageal

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21
Q

which is more hydrophilic - the epidermis or the stratum corneum?

A

epidermis

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22
Q

explain the difference between absorption through the GI tract and absorption through the skin

A

for the GI, the drug first has to dissolve in aqueous phase and then partition through lipid phase

it is the opposite for skin absorption because the epidermis comes after the stratum corneum and the stratum corneum is more lipophilic

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23
Q

how can penetration through the skin be enhanced?

A

through use of a chemical enhancer to disrupt the phospholipids and make it easier for the drug to get through the stratum corneum

also, absorption can be enhanced through hydration of the skin

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24
Q

true or false

the drug should have a greater physiochemical attraction to the skin than to the vehicle

A

TRUE – so that the drug will leave the vehicle

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25
Q

what is the “horny layer”?
how does it affect drug absorption through the skin?

A

stratum corneum

the thinner the stratum corneum, the greater percutaneous absorption

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26
Q

name 7 physiological conditions of the skin that may have an impact on the penetration of the drug

A

bonding
sebum
hydration
thickness
injury
metabolism
temperature

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27
Q

explain how “bonding” is a physiological condition of the skin that may have an impact on the penetration of the drug

A

the accumulation of bonding in the epidermis can decrease the initial transport of the drug

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28
Q

explain how sebum in the skin can affect the penetration of the drug through the skin

A

can alter the pH, and the amount and composition of sebum can alter the passage of the drug

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29
Q

true or false

increased hydration usually decreases penetration rate

A

FALSE - usually increases

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30
Q

what can increase hydration?

A

occlusive dressings

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31
Q

how can hydration vary across the skin

A

the age of the skin
the location of the skin
the condition of the skin

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32
Q

where on our body is the skin very thin?
where very thin?
what does this say about the absorption rate?

A

thin = behind ear
thick = palm of hand

follows Fick’s first law - very small thickness = easier absorption

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33
Q

explain how injury affects drug absorption through the skin

A

skin that is cut increases the penetration rate, but applying a transdermal patch may cause irritation and should be avoided

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34
Q

explain how metabolism can affect percutaneous drug absorption

A

1st pass effects used to be thought to be that drugs were destroyed at the FIRST ENCOUNTER to the body. however, this is not true anymore

we don’t normall have a lot of enzymes hanging around near our skin - they’re in the liver.

in theory tho, increased metabolism causes reduced penetration of the drug

35
Q

name 2 factors that affect metabolism (skin)

A

-age
-skin condition

36
Q

what is the normal temperature of our skin?

A

~30 degrees celsius

37
Q

name 3 percutaneous absorption enhancers

A

-chemical enhancers
-iontophoresis
-sonophoresis

38
Q

explain how chemical enhancers enhance percutaneous absorption

A

the increase the skin permeability by REVERSIBLY damaging or altering the physiochemical nature of the stratum corneum. reduces its resistance to diffusion

they cause hydration of the skin and the structure of the lipids and lipoproteins in the intercellular channels are altered

39
Q

name 3 chemical enhancers

A

alcohol
azone
DMSO (dimethyl sulfur oxide)

40
Q

explain how azone and DMSO differ in their functions as chemical enhancers

A

azone gets inserted between lipid bilayers which increases the permeation of the drug through the intercellular pathway

DMSO SOLVATES the polar heads of the phospholipids which expands the aqueous region

41
Q

differentiate between iontophoresis and sonophoresis.

what are they used for?

A

used as percutaneous permeation enhancers.

iontophoresis = delivery of a charged chemical compound across the skin membrane by using an ELECTRICAL FIELD

sonophoresis = used at high frequency ultrasound to increase permeation. the sound waves increase the separation between the cells of the stratum corneum

42
Q

__________ is(are) PHYSICAL method(s) of increasing drug permeation through the skin

A

iontophoresis and sonophoresis

43
Q

define the major barrier of the skin

A

the stratum corneum

44
Q

what are the percutaneous absorption models?

A

-in vivo studies (animals)
-in vitro studies (2 layer models of the skin - side by side and up and down models. - follows Fick’s first law)

45
Q

explain the advantages/benefits of the 2 in vitro percutaneous absorption models available

A

the “up and down” model poses an issue when air gets to the top and becomes a barrier

the “side by side” model solves this issue

46
Q

in the side by side absorption model, the dermis faces the ___ compartment and the epidermis faces the _____ compartment

in the up/down absorption model, the dermis faces __ and the epidermis faces ___

A

dermis faces donor compartment and epidermis faces receptor compartment

epidermis faces down and dermis faces up

47
Q

which has looser tissue - the epidermis or the stratum corneum

A

epidermis

48
Q

“an application of physical-chemical properties to predict absorption expectation through biological membranes”

A

membrane permeability studies

49
Q

according to membrane permeability studies…..

A

Fick’s first law is followed.
as conc of the drug increases, the rate of diffusion also increases

50
Q

membrane permeability studies used what kind of invitro equipment?

A

the side by side model (with dermis facing donor compartment and epidermis facing receptor)

51
Q

an early assessment of the passage of drugs across biological membranes

A

membrane permeability studies

52
Q

“passive absorption mechanism”

A

Fick’s first law

53
Q

name and differentiate between the 2 transdermal delivery systems

A

matrix type (monolithic)
membrane type

monolithic system (matrix type) – has a drug matrix layer between the backing and frontal layers

membrane-controlled systems – contains a drug reservoir (or pouch) usually in liquid or gel form, a rate-controlling membrane, and backing, adhesive, and protecting layers

54
Q

true or false

the membrane system cannot give zero order drug release

A

FALSE - IT CAN

matrix type cannot

55
Q

what does zero order mean

A

the rate does not vary with the increase or decrease of the concentration of the reactants (drug)

56
Q

what is the 5 layer, bulky, matrix type patch?

A

Nitro dur

57
Q

what component of transdermal delivery systems is included to ensure that the drug will only move unidirectionally?

A

the backing layer

58
Q

true or false

if the drug is capable of providing an adhesive, an additional adhesive layer is still needed

A

FALSE – not needed

in the case of matrix type, there is no adhesive layer and the drug itself serves as the adhesive

59
Q

the drug reservoir for membrane type is a solution or gel.

what about the drug layer in matrix type system?

A

it is a POLYMER

60
Q

increased vehicle viscosity in transdermal delivery systems ____ diffusion coefficient

A

REDUCES

61
Q

______concentration/solubility of a drug penetrates better in TDDS

A

high

62
Q

true or false

lower concentration gradient = better penetration

A

false

higher concentration gradient = better penetration

63
Q

which increase penetration – nonaqueous vehicles or aqueous vehicles? in the case of TDDS

A

nonaqueous vehicles (occlusive)

64
Q

in the case of TDDS, _ area causes increased absorption

A

increased area

65
Q

name 6 design objectives for transdermal delivery systems

A

-deliver the drug for percutaneous absorption at therapeutic levels at optimal rate

-contain med agents that can release from the system and partition into the stratum corneum

-occlude the skin to ensure ONE WAY FLUX (dc/dt) into the stratum corneum

-have therapeutic advantage over other dosage forms

-not irritate or sensitize the skin

-adhere well to the skin and have the size, appearance, and site placement that encourage acceptance

66
Q

in order to ensure that the drug can be released from the system and partition into the stratum corneum……..

A

it must have the necessary physiochemical characteristics

67
Q

name 8 advantages of transdermal delivery systems **

A

-avoid GI absorption difficulties
-substitute for oral administration

-avoid first pass effect

-noninvasive and no inconvenience of parenteral therapy

-may be terminated fast

-provide extensive therapy with a single application

-extend the activity of the drugs having short half life

-easily and rapidly used in emergencies

68
Q

an advantage of TDDS is avoiding GI drug absorption difficulties.
explain this further

A

-low pH
-enzymatic activity
-drug interaction with food/drink and other oral drugs

69
Q

an advantage of TDDS’s is that they extend the activity of drugs having a short half life.
explain this further

A

there is a reservoir of drug in the delivery system and its release is controlled

70
Q

drugs with ___ half life are not suitable to be formulated as a transdermal patch

A

long half life

there’s no point. if you already take 1 tablet a day you would still have to apply the patch every day or so

71
Q

name 6 disadvantages of TDDS

A

-only potent drugs are suitable
-contact dermatitis at application site
-limited time that they can stay (due to rashes and sensitization)
-variable intra and inter percutaneous absorption efficacy (everyone has different skin)
-bacterial and enzymatic drug metabolism under the patch
-complex tech/high cost

72
Q

WHY can only relatively potent drugs be suitable candidates for drug delivery?

A

the skin is impermeable – natural limit of drug entry

73
Q

true or false

TDDS are cheap and easy to make

A

false – complex tech needed and expensive

74
Q

true or false

percutaneous absorption does not vary with the site of application

A

FALSE - it does vary

75
Q

TDDS’s should be applied to what kind of skin

A

clean and dry skin

76
Q

true or false

skin lotion should be used before applying a transdermal patch

A

FALSE

has to be intact, original skin.
lotion will impact the drug release from the patch

77
Q

true or false

transdermal delivery systems should NOT be physically altered by cutting

A

true

78
Q

true or false

a transdermal delivery system should always be worn for the full period stated in the product instructions

A

FALSE – not the case for nitroglycerin bc of tolerance effect

but for all other cases it is true

79
Q

what should the patient do with a TDDS after they remove it? why?

A

fold it in half with the adhesives facing each other so it can’t be reused.

after 24 hrs there’s still a lot remaining in the patch. ~20% used after 24 hours

80
Q

why is skin irritation a major issue for TDDS

A

lot of excipients and any possible chemical enhancers

81
Q

name 7 limitations of TDDS

A

-not for all drugs
-limited time it can be affixed
-variable inter and intra percutaneous absorption efficacy
-skin rashes, sensitization
-bacterial and enzymatic drug metabolism under the patch
-complex tech/ high cost

82
Q

what drugs can NOT be used in a transdermal patch

A

if the drug is not potent
sometimes, drugs with a short half life require a loading dose, and transdermal patches can’t deliver this high dose

also kind of useless for drugs with long half lives

83
Q

of the patches mentioned, which remains on the skin the longest

A

7 days - transdermal clonidine (Catapres-TTS)

84
Q
A

Pharmaceutics II Exam 2 (7 decks)

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