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PHAR224 > Percutaneous Absorption > Flashcards

Percutaneous Absorption Flashcards

1
Q

What is percutaneous absorption?

A

absorption through the skin
the amount of drug that passes from the vehicle into the stratum corneum of the skin

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2
Q

How does partitioning of the drug take place?

A

diffusion
-driven by concentration gradient at each level

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3
Q

What is the primary permeability barrier?

A

stratum corneum

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4
Q

What is the rate-limiting step of percutaneous absorption?

A

diffusion through the stratum corneum

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5
Q

Why do we call skin a passive barrier to substances?

A

it allows movement of molecules from a region of higher concentration to a region of lower concentration based on concentration gradient

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6
Q

What are the routes of percutaneous absorption?

A

across stratum corneum
-transcellular or intercellular
via appendages
-sweat ducts, sebaceous glands, hair follicles

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7
Q

Are appendages a route of percutaneous absorption that is more pronounced for drug absorption or microbial activity?

A

microbial activity

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8
Q

What are the drugs factors that influence percutaneous absorption?

A

concentration of the drug in the preparation (to provide a high conc gradient across the skin)
partition coefficient
drug/skin binding

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9
Q

What is the partition coefficient?

A

stratum corneum-to-vehicle partition
ratio of the drug concentration in the stratum corneum to the drug concentration in the vehicle
measure of the lipophilicity of a drug and is an indication of its ability to cross the lipid barrier

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10
Q

What are the vehicle factors that influence percutaneous absorption?

A

pH
-determines ionization of the drug thus absorption
co-solvents
-define concentration of drug on the skin
release of drug from vehicle
-optimize with the appropriate vehicle
penetration enhancers
-temporarily increase permeability of the skin

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11
Q

What are the skin factors that influence percutaneous absorption?

A

age of the skin
skin condition (hydration, disease state)
thickness of stratum corneum (eye vs palm)
skin metabolism
circulation effects
species differences

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12
Q

What is the in vitro method for studying percutaneous absorption?

A

diffusion cell techniques (Franz cell)
-helps to read diffusion of drugs from ointments, creams, and gels
-important for testing batch-to-batch variation

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13
Q

What are the in vivo methods for studying percutaneous absorption?

A

animal models
-pig (closest to human)
-guinea pig
-monkey
-hairless mouse
-rabbit

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14
Q

What is the Blanching test?

A

qualitatively assesses topical availability and potency of corticosteroids
-uses the skin-whitening side to estimate the rate and extent of corticosteroid diffusion to the dermal vasculature
-intensity of whiteness correlates directly with the topical availability of the drug

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15
Q

Which equation do we use to determine the rate of diffusion through the skin?

A

Ficks Law

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16
Q

What are the two phases during diffusion across the skin (according to Ficks Law)?

A

drug concentration at the vehicle/skin interface
-drug first accumulates at the interface, this causes the drug concentration to rise at the interface
sink effect (concentration drops drastically)
-the drug does not stay at the interface, partitions into the receiver compartment

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17
Q

Describe movement of the drug from the donor to the receiver compartment.

A

NOT linear
driven by the concentration gradient at the interface
you can measure the amount of drug present in the vehicle and the drug absorbed in the skin, you CANNOT measure the drug at the interface (hence why Ficks Law developed to calculate the partition of the drug at the interface to give an idea of the amount of drug that should be in the vehicle to drive this gradient)

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18
Q

What is the diffusion coefficient?

A

the amount of a particular drug that diffuses across a unit area of the stratum corneum in 1s under the influence of a concentration gradient

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19
Q

What is the permeability coefficient?

A

a quantitative measure of the rate at which a molecule can cross a membrane such as a lipid bilayer

20
Q

What is the equation for Ficks Law?

A

J=(DP/S)CV
J: solute flux
D: solute diffusion coefficient
P: solute partition coefficient
S: thickness of the stratum corneum
CV: difference in solute concentration between vehicle and tissue

21
Q

What is the relationship between partition coefficient and penetration?

A

large the partition coefficient–>better penetration
=more effective the formulation

22
Q

What is the main idea of a dermatological preparation?

A

build high concentration of drug locally
minimize systemic exposure to limit SE

23
Q

What is the main difference between dermal and transdermal preparations?

A

transdermal are intended to pass the skin and achieve systemic levels

24
Q

What are the main dermatological treatments being targeted at the stratum corneum?

A

emollients and moisturizers (increase hydration)
protective films (barrier crms/oint, sunscreens)
topical antibiotics (epidermal infections)
keratolytics/exfolients (SA, BP)

25
Q

What are the main dermatological treatments being targeted at the epidermis and dermis?

A

topical steroid and NSAID agents
local anesthetic agents
antihistamines/antipruritics
anticancer drugs (antimetabolites)
some acne meds (immunomodulators)

26
Q

What are the main dermatological treatments being targeted at skin appendages?

A

antiperspirants (sweat glands)
depilatories
antibiotics (clindamycin, tetracycline, erythromycin)
antifungals (clotrimazole, miconazole)
for bacterial and fungal folliculitis

27
Q

What are the main treatments being targeted with systemic treatment via percutaneous absorption (patches)?

A

motion sickness (scopolamine)
angina (nitroglycerin)
hypertension (clonidine)
smoking cessation (nicotine)
birth control patches

28
Q

When are ointments preferable?

A

where occlusion is required
where longer retention period is required
avoid oleaginous bases in oozing conditions but bases with water absorbing capability can be used in oozing wounds

29
Q

What are common practice scenarios where ointments are preferred?

A

kids (reduce frequency of application)
psoriatic lesions, eczema flares (overcome skin breaking due to dryness)

30
Q

When are creams preferable?

A

where emollient action is required without occlusion
better patient acceptance

31
Q

What are common practice scenarios where creams are preferred?

A

when frequency of application is not a concern (ex: adults)
maintenance therapy of eczema (skin hydration)

32
Q

When are lotions preferred?

A

where low viscosity and high flowability is intended
where large surface area is to be treated

33
Q

What are common practice scenarios where lotions are preferred?

A

hairy skin areas
where cooling and drying effect is required like inflamed irritated insect bites

34
Q

When are gels preferred?

A

where API is highly water soluble
emulgel concept:
-where cooling/drying effect is preferred
-where faster release is desirable

35
Q

What are common practice scenarios where gels are preferred?

A

topical pain management
oily skin conditions
do not use when skin is prone to drying or irritation

36
Q

When are pastes preferred?

A

high amount of API has to be incorporated
where more barrier properties are required like oozing conditions
offer longer retention time

37
Q

What are common practice scenarios where pastes are preferred?

A

diaper rashes
aphthous ulcers in mouth (resistance against med being washed away by saliva)
treatment of warts where longer residence of SA is required

38
Q

What is the use of topical corticosteroids?

A

relief of inflammation and pruritis

39
Q

What occurs when C9 of steroids is fluorinated?

A

increases anti-inflammatory activity (potency)

40
Q

When occurs when you add substituents to C17 or C21 of steroids?

A

influences solubility
-more lipophilic=increased penetration

41
Q

What occurs when you add a-alkyloxycarbonyl dervatives to C16 of steroids?

A

antedrug concept
-decreases systemic side effects

42
Q

What are the classes of topical steroids?

A

superpotent (1)
high (2 and 3)
intermediate (4 and 5)
low (6 and 7)

43
Q

What is the most common side effect of topical steroids?

A

skin thinning
-sparing application is advised

44
Q

What occurs as potency of topical steroids increases?

A

increases side effects

45
Q

What is the preferred site of use and potential for irritation of the following:
-ointment
-cream
-gel
-lotion

A

ointment:
-thick plantar or palmar skin
-avoid occluded areas like groin
-potential for irritation: low
creams:
-moist skin and intertriginous areas
-potential for irritation: depends on excipients
gels:
-occluded areas, oily and mucosal surfaces
-potential for irritation: high
lotion:
-occluded and hairy areas
-potential for irritation: depends on excipients

46
Q

What is the effect of penetration enhancers on topical corticosteroids?

A

increased Kp 15-30x
-dont use for high potency crms/oint

PHAR224 (7 decks)

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