Skin Content Flashcards
Give a drug that was once used for oral route but changed into topical delivery
Rivastigmine
What are the two properties with relative ease of permeation in skin
- Lipophilic molecules are delivered better compared to hydrophilic
- Lower melting point is better absorbed
What are the pharmacokinetic properties an ideal topical drug should have
- Molecular weight: 300 - 500
- Log P: 1-3.5
- Aqueous solubility: >100mg/mL
How do you estimate drug flux
Using mathematical models of empirical relationships between flux, log P, solubility and molecular weight
Works alright for mid range molecules and small moderately lipophilic molecules
What are the different phases of liquid formulation and its advantages
- Allows rapid short term drug input into skin
- Single phase: non polar solution (oils) example: liquid paraffin
- Two phase: Dilute emulsions (o/w and w/o) found in lotions
- Multi phase: Dilute multiple emulsions (o/w/o or w/o/w)
What are the different phases of semisolid formulation and its advantages
- Has increased residency time on sin
- Single phase: ointment (dissolved medicaments)
- Two phase: Emulsions (o/w or w/o) dispersed medicament that include creams
- Multi phase: Multiple emulsions with dispersed medicaments (cream pastes)
What are the different phases of solid formulation and its advantages
- Extended drug delivery via skin
- Single phase: Powders
- Two phase: Transdermal patches (some)
- Multi phase: Complex transdermal patches
What are the different skin types and what formulation of topical delivery should you use on them?
- Normal to oily: Gels
- Normal to dry: Lotions
- Dry skin: creams
- Hairy: lotions, gels, sprays
- Intertriginous areas: rubbing of two skins (arm pit): creams or lotions
How do you treat a wet, vesicular or weeping lesion
Using creams, lotions or gels
Hydrophilic drugs: aqueous system water, co solvents of propylene glycol and avoiding alcohols
Hydrophobic drugs: mineral oils
How do you treat a dry, thickened scaly leision
Fatty formulation like ointments and pastes
Oil and waxes contain surfactants, glycol depends on formulation and drug solubility
How do you target a normal intact stratum corneum to enhance skin delivery
- Aqueous or oil based formulations containing alcohols, glycols, oleic acid
- Isopropyl myristate, propylene glycol
What is the typical bioavailability of topical creams and gels and patches
- Topical creams and gels: 1-3%
2. Patches: 30-70% of drugs
What is the most appropriate properties the formulation of drug should have
- Designed to have appropriate release of drug, rapid release or slow (7 day patch)
- Contains MODERATELY LIPOPHILIC DRUG in LIPOPHILIC OILY BASE
- Vehicle should allow solubility of drug but not retain the drug by being a good solvent
What is the most desirable thermodynamic property
Saturated solutions: Kp is fixed for given molecule
Gives maximum driving force for diffusion, maximum concentration gradient through skin
What does occlusion allow and give an example of a product that uses this
- Helps stratum corneum equilibrate with underlying wet epidermis
- Stops transepidermal water loss (TEWL)
- Hydrates tissue
- Promotes delivery of hydrophilic and hydrophobic compounds
- Product: EMLA cream applied with occlusive dressing
What is an enhancer
- Chemicals that interact reversibly with skin to promote drug flux
- Typical: disrupts stratum corneum and intercellular lipid structure
- Alters transcellular keratin conformation
Give an example of an enhancer
Solvents: EtOH, propylene glycol Surfactants: SLS Fatty acids, oleic acid Urea Mineral oils, silicone oils
What is bioequivalence in comparing hydrocortisone and clobetasol
No significant difference in rate and extent of absorption
What is the most common patch and describe what it consists of
- Drug in adhesive (DIA)
- Pressure sensitive adhesive, backing and release liner
- Can incorporate solvents, surfactants and fragrances
What are the advanced formulations used in drug skin delivery
- Heat- double delivery
- Ablation of skin; lasers and radio waves
- Similar principle when treating wart- remove callus skin
What is a liposome
- Lipid vesicles that enclose an aqueous volume
- Formed from phospholipids and possibly cholesterol
- Can trap hydrophilic molecules in an aqueous core or lipophilic materials within membrane
Give examples of liposome
- Niosomes: non ionic surfactant
- PEGylated: increases circulation residence
- Ethosomes: high ethanol content, soft phospholipid vesicles
- Transfersomes: derformable liposomes
An example of a commercial liposome
amBisome
Formed with amphotericin B in liposomes
What are good targets for liposomes for which skin conditions
Pilosebacceuous units
Used to treat acne, cancers and for systemic delivery
What is iontophoresis
Electrical charge used to repel ionic molecules e.g. positive canon repelled by positive cathode
Drives molecule into skin
Can also get convective flow of water
What are micro needles used for and their future use
Penetrate into strateum corneum, but no pain receptors
Delivery of large proteins, antibodies, hormones, vaccines
