Transdermal drug delivery system (TDDS) formulation approaches and evaluation are essential topics for B.Pharm students learning how to design safe, effective patches. This introduction covers key concepts: matrix and reservoir systems, rate-controlling membranes, backing layers, adhesives, permeation enhancers, and microneedle/iontophoresis strategies. Important formulation considerations include drug physicochemical properties (molecular weight, lipophilicity, daily dose), polymer selection, and patch design to control release kinetics and skin permeability. Evaluation techniques involve in vitro release, Franz diffusion cell studies, adhesion/tack testing, skin irritation assessment, and stability. Understanding these aspects ensures rational TDDS design and regulatory compliance. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which of the following is a common design type of transdermal patches?
- Matrix-type patches
- Tablet-type patches
- Capsule patches
- Syringe patches
Correct Answer: Matrix-type patches
Q2. What is the typical molecular weight cutoff often recommended for drugs suitable for TDDS?
- Less than 500 Da
- Greater than 1000 Da
- Between 800 and 1200 Da
- Exactly 600 Da
Correct Answer: Less than 500 Da
Q3. Which component of a transdermal patch primarily ensures adhesion to the skin?
- Adhesive layer
- Backing layer
- Release liner
- Rate-controlling membrane
Correct Answer: Adhesive layer
Q4. A reservoir-type TDDS typically contains:
- Drug solution separated by a rate-controlling membrane
- Drug uniformly dispersed in a polymer matrix
- Drug in a tablet core
- Dry powder drug layer
Correct Answer: Drug solution separated by a rate-controlling membrane
Q5. Which property of a drug increases its suitability for skin permeation in TDDS?
- Balanced lipophilicity (log P around 1–3)
- Extremely high hydrophilicity
- Very large molecular size
- High melting point above 300°C
Correct Answer: Balanced lipophilicity (log P around 1–3)
Q6. Which in vitro apparatus is most commonly used to evaluate skin permeation of TDDS?
- Franz diffusion cell
- Rotating drum tester
- Brookfield viscometer
- Disintegration tester
Correct Answer: Franz diffusion cell
Q7. Which test measures the force required to remove a patch from the skin at a fixed angle?
- Peel test (peel strength)
- Tack test (rolling ball)
- Tensile strength test
- Moisture sorption test
Correct Answer: Peel test (peel strength)
Q8. A key advantage of matrix TDDS over reservoir TDDS is:
- Lower risk of dose-dumping
- Unlimited drug loading capacity
- Ability to deliver large proteins intact
- No need for adhesive
Correct Answer: Lower risk of dose-dumping
Q9. Which polymer is commonly used as a pressure-sensitive adhesive in TDDS?
- Acrylic polymers
- Polyvinyl chloride
- Polyethylene glycol 4000
- Sodium alginate
Correct Answer: Acrylic polymers
Q10. Permeation enhancers in TDDS function primarily by:
- Reversibly disrupting stratum corneum lipids
- Increasing blood flow under the patch
- Increasing drug metabolism in skin
- Hardening the stratum corneum
Correct Answer: Reversibly disrupting stratum corneum lipids
Q11. Which evaluation parameter assesses chemical integrity of the drug in a patch during storage?
- Assay and content uniformity
- Peel adhesion
- Tack measurement
- Thickness uniformity
Correct Answer: Assay and content uniformity
Q12. In release kinetics, a zero-order release from a TDDS implies:
- Constant drug release rate over time
- Release proportional to square root of time
- First-order decline in release rate
- No drug is released
Correct Answer: Constant drug release rate over time
Q13. Which skin model is often used as a human skin substitute in permeation studies?
- Porcine ear skin
- Rabbit intestinal mucosa
- Silicone rubber membrane
- Chicken eggshell
Correct Answer: Porcine ear skin
Q14. Which test assesses the irritancy potential of a TDDS on skin?
- Skin irritation/sensitization test
- Franz cell diffusion test
- Viscosity measurement
- Loss on drying
Correct Answer: Skin irritation/sensitization test
Q15. Which layer in a patch provides mechanical protection and blocks moisture loss?
- Backing layer
- Rate-controlling membrane
- Adhesive layer
- Release liner
Correct Answer: Backing layer
Q16. Which technique can enhance transdermal delivery using a small electrical current?
- Iontophoresis
- Sonophoresis
- Electroporation
- Microneedling
Correct Answer: Iontophoresis
Q17. For which drug characteristic is low daily dose most important for TDDS suitability?
- Potency (dose requirement <10–20 mg/day)
- High water solubility
- Extensive first-pass activation
- Large molecular weight
Correct Answer: Potency (dose requirement <10–20 mg/day)
Q18. Which analytical method is commonly used to quantify drug in patch content and release samples?
- High-performance liquid chromatography (HPLC)
- Polarimetry
- Karl Fischer titration
- Flame photometry
Correct Answer: High-performance liquid chromatography (HPLC)
Q19. What does IVIVC stand for in transdermal formulation evaluation?
- In vitro–in vivo correlation
- Internal validation of in vivo components
- Immediate versus intravenous comparison
- Invariable viscosity in various conditions
Correct Answer: In vitro–in vivo correlation
Q20. Which problem is a major regulatory concern for reservoir TDDS?
- Risk of dose-dumping if membrane ruptures
- Excessive breathability
- Insufficient adhesive tack
- Lack of backing layer
Correct Answer: Risk of dose-dumping if membrane ruptures
Q21. Microneedle-assisted TDDS primarily facilitates drug delivery by:
- Bypassing the stratum corneum barrier via microchannels
- Increasing systemic blood flow
- Changing drug chemistry in situ
- Absorbing moisture from the skin
Correct Answer: Bypassing the stratum corneum barrier via microchannels
Q22. Which parameter evaluates how quickly a patch initially sticks to skin?
- Tack
- Peel strength
- Thickness uniformity
- Water vapor transmission rate
Correct Answer: Tack
Q23. The rate-controlling membrane in a reservoir TDDS primarily controls:
- Drug diffusion rate from reservoir to skin
- Patch adhesion to skin
- Water uptake from the environment
- Mechanical strength of the backing layer
Correct Answer: Drug diffusion rate from reservoir to skin
Q24. Which stability condition is commonly used for accelerated stability testing of TDDS?
- 40°C and 75% RH
- 0°C and 10% RH
- 25°C and 10% RH
- 100°C and 5% RH
Correct Answer: 40°C and 75% RH
Q25. Which method measures drug release from a patch into a finite volume of receptor fluid over time?
- In vitro release testing (IVRT)
- Mucoadhesion testing
- Disintegration testing
- Minimum inhibitory concentration
Correct Answer: In vitro release testing (IVRT)
Q26. Which of the following is NOT a desired characteristic of an ideal transdermal drug?
- High daily dose requirement (e.g., >100 mg/day)
- Potent pharmacological activity
- Low molecular weight
- Favorable log P for skin permeation
Correct Answer: High daily dose requirement (e.g., >100 mg/day)
Q27. Which evaluation checks uniform thickness and size of manufactured patches?
- Physical dimension and thickness uniformity
- Spectrum analysis
- Microbial limit test
- pH measurement
Correct Answer: Physical dimension and thickness uniformity
Q28. Which enhancer class includes oleic acid and azone used in TDDS?
- Lipid-disrupting chemical enhancers
- Surfactant-free enhancers
- Proteolytic enhancers
- Enzymatic enhancers
Correct Answer: Lipid-disrupting chemical enhancers
Q29. What is the main reason to perform skin adhesion tests under simulated use conditions?
- To predict clinical patch retention and patient acceptability
- To increase drug potency
- To reduce manufacturing cost
- To sterilize the patch
Correct Answer: To predict clinical patch retention and patient acceptability
Q30. Which assessment helps determine whether the in vitro release predicts in vivo drug absorption?
- Establishing an IVIVC (in vitro–in vivo correlation)
- Measuring tack
- Conducting a peel test
- Checking backing layer opacity
Correct Answer: Establishing an IVIVC (in vitro–in vivo correlation)
