40 Questions
What is the outermost layer of the epidermis?
Horny layer
What is the main barrier function of the skin?
Stratum corneum
What affects drug release from TDDSs and skin penetration?
Both A and B
What is the equation for Fick's first law of diffusion?
J=P.D.A.ΔC/h
What is the importance of lipophilic drugs in transdermal delivery?
They are effective in transdermal delivery due to the lipoid nature of the stratum corneum
What is the diffusional path length across the skin layers?
h
What is the unit of Flux (J) in Fick's first law of diffusion?
amount of drug permeated per unit area, per unit time
What is the importance of water solubility in transdermal delivery?
It is necessary for transdermal delivery
What is the main advantage of transdermal drug delivery systems over oral administration?
Avoiding first pass metabolism
What is the benefit of transdermal drug delivery systems in terms of patient compliance?
Reduced frequency of dosing
What is a limitation of transdermal drug delivery systems?
Only suitable for highly potent drugs
What is the mechanism of drug release from transdermal drug delivery systems?
Release of the drug from the vehicle and diffusion through the lipophilic stratum corneum
What is a disadvantage of transdermal drug delivery systems?
Local skin reaction can occur
What is the benefit of transdermal drug delivery systems in terms of drug levels?
Constant drug release rates
Why are transdermal drug delivery systems suitable for self-medication?
They are easy to apply
What is a substitute for oral medication when it is not suitable?
Transdermal drug delivery systems
What is the main purpose of a liner in a transdermal patch?
To protect the patch during storage
What type of system has a drug reservoir held between the backing layer and the rate-controlling membrane?
Reservoir system
In which type of system is the drug uniformly dispersed in a polymer matrix?
Matrix system
What is the main difference between a reservoir system and a micro-reservoir system?
The combination of reservoir and matrix dispersion
What is the name of the patch used for prophylaxis from motion sickness?
Transdermscop
Which patch is used for the treatment of angina pectoris?
All of the above
What type of system has the drug mixture sandwiched between the liner and backing?
Drug-in-adhesive system
What is the name of the patch used for the treatment of diabetes mellitus?
Glimepiride patch
Why is it important for a drug to have both lipophilicity and hydrophilicity?
To allow it to cross the lipophilic stratum corneum and the aqueous viable epidermis
What is the rate limiting step for drug absorption?
Drug partitioning between the stratum corneum and the vehicle
What is the effect of increasing the drug partition coefficient (P)?
The flux (J) of the drug increases
What is the effect of increasing the surface area of the applied drug (A)?
The flux (J) of the drug increases
What is the effect of increasing the drug concentration (ΔC)?
The flux (J) of the drug increases
What is the effect of decreasing the diffusional path length of the drug across the skin layers?
The flux (J) of the drug increases
What is the purpose of chemical permeation enhancers?
To temporarily reduce the permeability barrier of the skin
What is the formula for ΔC?
Cv - Cs
What is the process of preparing a transdermal drug?
Suspending drug solids in an aqueous solution of a water-soluble liquid polymer and then uniformly dispersing the solution in a lipophilic polymer
What is Asenapine used to treat?
Antipsychotic
What is the application site of Buprenorphine?
Upper outer arm, upper chest, or upper back
What is the duration of Clonidine?
7 days
What is Oestradiol used to treat?
Female HRT
What is the application site of Oestradiol?
Trunk of the body including the buttocks and abdomen
When was Asenapine approved by the FDA?
2009
What is the patch design of Clonidine?
Reservoir/Membrane
Study Notes
Transdermal Drug Delivery Systems (TDDSs)
- Definition: Transdermal drug delivery (TDD) is the delivery of active pharmaceutical ingredients (APIs) through the skin into the bloodstream to produce systemic effects.
- Advantages:
- Avoid first-pass metabolism, enhancing bioavailability and therapeutic efficacy of certain drugs
- Avoidance of GIT irritation and degradation
- Minimizing undesirable side effects
- Providing controlled drug release, reducing the frequency of dosing and enhancing patient compliance
- Easy to terminate drug input by simply removing the transdermal patch
- Suitable for self-medication and avoiding the risk and inconvenience of parenteral therapy
- Providing a substitute when oral medication is not suitable (e.g., in cases of vomiting and diarrhea)
- Disadvantages:
- Local skin reaction can occur due to irritancy of some drugs
- Limited to potent drugs (therapeutically effective in small doses) and drugs of low molecular weight (Molecules lower than 500 Daltons)
- Skin enzymes may metabolize some drugs
- May be non-economical, and patch failure may occur
Mechanism of Drug Release from TDDSs
- The drug is released from the vehicle
- Then, diffusion of the drug through the lipophilic stratum corneum and crossing to the more aqueous viable epidermis
- Then, continuing from the avascular epidermis to the highly perfused dermis layer
- Uptake to the microcirculation to the systemic circulation, then to the affected area
Factors Affecting Drug Release from TDDSs and Skin Penetration
- Skin barrier properties
- Physicochemical properties of the drug
- Drug solubility
- Drug partition coefficient
- Surface area of the applied drug
- Drug concentration
- Diffusional path length of the drug across the skin layers
- Molecular weight of drug molecules
Fick's First Law of Diffusion
- J = P.D.A.ΔC/h
- Where J is the flux (rate of drug permeation across the skin), P is the partition coefficient, D is the diffusion coefficient, A is the surface area of the applied drug, ΔC is the drug concentration gradient across the skin, and h is the diffusional path length across the skin layers
Types of Transdermal Patches
- Drug-in-Adhesive System
- Examples: Isosorbidedinitrate- (Frandoltape) for treatment of angina pectoris, Zolmitriptan TDDS for treatment of migraine
- Reservoir System
- Examples: Nitroglycerine (Deponit patches) for angina pectoris, Scopolamine (Transderm Scop) for prophylaxis from motion sickness
- Matrix System
- Examples: Nitro-Dur patch for treatment of angina pectoris, Glimepiride patches for treatment of diabetes mellitus
- Micro-Reservoir System
- Combination of reservoir and matrix dispersion system
Some Transdermal Drugs for Systemic Delivery Launched in the USA and EU
- Asenapine (Secuado, 2009) for antipsychotic treatment
- Buprenorphine (Butrans, 2010) for chronic pain
- Clonidine (Catapres-TTS, 1984) for hypertension
- Oestradiol (Estraderm, 1986) and Oestradiol (Climara, 1994) for female HRT
Learn about Transdermal Drug Delivery Systems, an alternative to oral and parenteral drug delivery, which administer agents through the skin. Test your knowledge on TDDSs and their effectiveness in drug delivery.
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