IC18 - Pharm Tech 3 Flashcards
What is the primary barrier to drug crossing skin via transdermal route?
Stratum corneum
Compare and contrast between transdermal and topical delivery?
- Topical: shallow skin penetration. local delivery
- Transdermal: Deep skin penetration, systemic delivery
What are the 5 advantages of transdermal delivery?
- Controlled release (reservoirs, duration of contact) > Decreased dosing frequency
- No GI degradation/irritation
- Bypasses hepatic first pass effect
- Easy termination of input
- Non invasive
List the 7 disadvantages and barriers to transdermal delivery.
- Variability between people and location of administration on body
- Stratum corneum > Slow absorption
- Skin irritation (interactions and removal)
- Could be removed by the patient
- Metabolic enzymes
- Blood brain barrier (via systemic delivery)
- Systemic side effects
What are the 8 factors that can affect transdermal delivery of drug?
- Skin condition: age, disease, injury, site
- Skin thickness (thickness of diffusion layer)
- Hydration of skin (stratum corneum)
- Stimulation of the skin
- Physicochemical properties of drug
- Permeation enhancers
- Concentration gradient
- Area of contact between formulation and skin
What are the ideal drug characteristics for transdermal products?
- MW: <500Da
- H Bond donors: ≤5
- H bond acceptor: ≤10
- Log P: 1-3
- Unionised
List 2 types of formulation for transdermal system.
- Topical (gel, creams, ointments)
- Transdermal (patches)
What are the common excipients for patches?
- Preservatives
- Solvents/co solvents
- Viscosity modified
- Permeation enhancers
- Adhesives
What are the 4 considerations for drug release in polymer matrices?
- Diffusion coefficient of drug
- Surface area
- Concentration
- Porosity/tortuosity of polymer matrix - determined by intramolecular interactions (crosslinking, hydrogen bonds)
What is the purpose of sealed packaging of transdermal product?
- Maintain integrity of adhesive
- Maintain integrity of product
- Maintain hydration
List two materials used for packaging of transdermal patches.
- Plastic/polymer lining
- Aluminium lining
Briefly explain the design of the patches using the membrane design.
- Drug dispersed in a separate depot
- Rate controlling membrane limits the amount of drug release over time
Briefly explain the design of the patches using the matrix design.
Drug incorporated in a polymer matrix, separate to the adhesive layer
Briefly explain the design of the patches using the drug-in-adhesive design.
Drug combined with adhesive and released from this matrix
What is the purpose of backing layer in patches?
Protection of drug and contents
