Drug Delivery to the Skin - 2

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  • Created by: LBCW0502
  • Created on: 28-01-20 11:07
State the features of developing formulations (1)
Preformulation. Stability indicating assay development and validation. Formulation design and optimisation (drug delivery strategies). In vitro release/permeation/deposition/efficacy studies (further optimisation). Manufacture. Stability studies
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State the features of developing formulations (2)
Preclinical and clinical studies
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State features of the Franz diffusion cell (1)
Developing formulations, skin permeation. Membrane (drug release). Skin- human F/T, E/S, S/C, dermatomed, animal, cell monolayers or LSE, vehicle/drug applied to surface, cell left stirring for up to 48 h at 37 degrees Celsius
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State features of the Franz diffusion cell (2)
Drug content measured on skin surface, in skin layers and in receptor fluid
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State features of diffusion cells (1)
Multi-station Franz diffusion cell system. Receiver compartment, donor compartment. Samples measured at different time periods. Results from Franz diffusion cell. Plot – cumulative amount (mcg/cm^2) against time.
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State features of diffusion cells (2)
Time depends on the drug being used. Linear pattern, eventually plateaus. Lag time (delay). Linear portion of profile – slope determines permeation rate/flux (micrograms/cm^2/h). Steeper slope – more permeation into the skin
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State features of diffusion cells (3)
Need to consider lag time – depends on preference e.g. want a formulation with a delayed effect
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Describe features of skin permeation (1)
Surface of drug removed by wash/wipe off or receptor chamber, skin-mass balance, separation of layers, digestion, extraction of drug (analysis by LC, scintillation counting, immunoassay, bioassay). Drug metabolism and keratin binding
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Describe features of skin permeation (2)
Intact skin (autoradiography, fluorescence/confocal microscopy, histochemistry)
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Describe features of the use of different types of skin (1)
Human skin (ethical issues/safety, past history/treatment, age/location, what type of membrane-full thickness, epidermal sheet, Stratum corneum, dermatomed, cell monolayer, living skin equivalent). Animal skin (similar considerations, species)
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Describe features of the use of different types of skin (2)
Synthetic membrane (applicability, model lipophilic membrane e.g. silastic or just a support e.g. cellulose)
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What is an infinite dose?
<10% of drug is lost from donor, steady state is prolonged
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What is a finite dose?
Drug is depleted, more like in vivo conditions
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Describe features of skin conditions
Avoids back diffusion. Permeant should not exceed 10% of it saturated solubility in the receptor. Combinations of buffers, solvents, albumin and surfactants often used. Should not affect the integrity of the membrane
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Describe features of integrity
Verification of skin integrity. Model drugs with known permeation coefficients. Titrated water. Transepidermal water loss (TEWL). Skin resistance
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How long is the duration for skin permeation investigated?
No more than 48 h. Dependent upon assay sensitivity and formulation
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How are results usually expressed?
Normally expressed as either J (e.g. μg/cm2/h), Kp (cm2/h) or Q (amount at any given time)
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How are skin samples obtained (to quantify amount of drug in the skin)?
Punch biopsies (hole), tape ********* (stratum corneum), skin blanching (induce inflammation, apply drug to area, observe effect)
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How are skin samples analysed (to quantify amount of drug in the skin)?
Using ATR-FTIR, confocal microscopy, microdialysis, multiphoton microscopy
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Card 2

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State the features of developing formulations (2)

Back

Preclinical and clinical studies

Card 3

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State features of the Franz diffusion cell (1)

Back

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Card 4

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State features of the Franz diffusion cell (2)

Back

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Card 5

Front

State features of diffusion cells (1)

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