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PHRM 100 – PDD > PDD 13: Transdermal Drug Delivery > Flashcards

PDD 13: Transdermal Drug Delivery Flashcards

1
Q

What is transdermal drug delivery?

A

delivery of drugs from the surface of the skin through the various layers into the systemic circulation

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2
Q

What is the transdermal delivery system?

A

drug delivery system that supports the passage of a drug through the skin and into the systemic circulation

  • typically transdermal patches
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3
Q

What are the advantages of transdermal drug delivery?

A

avoids variables that PO drugs are subjected to:

  • pH (degradation, ionization)
  • enzymatic degradation and first-pass metabolism
  • gastric emptying time
  • interactions with food/drink and other PO drugs

avoids the risks and inconveniences of parenteral therapy

  • risk of infection
  • fear and pain
  • need for trained professionals
  • hazardous waste/disease transmission

possess the benefits of controlled drug delivery

  • reduced dosing frequency
  • reduced blood level fluctuations
  • reduced sub-therapeutic dosing
  • reduced systemic side-effects
  • extends utility of drug with short t1/2

therapy can be stopped by removal of the system

  • removal of the system will result in immediate discontinuation of drug input
  • results in gradual decline of the drug concentration in blood

easily identified for dosing and emergency purposes

  • many systems have identifying markings but many are clear for aesthetic reasons
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4
Q

Not all drugs are viable candidates for TDD. There needs to be good therapeutic rationale, and therefore not good for…

A
  • drugs with good PO bioavailability and infrequent dosing that are well-accepted by patients
  • drugs needing large and rapid bolus dosing
  • tolerance-inducing drugs
  • drugs requiring chrono-pharmacological management (ie. pulsatile administration)
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5
Q

What properties should drugs ideally have for transdermal delivery?

A
  • logP between 1-3
  • MW under 600 Da
  • high biological activity
  • and not cause skin irritation
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6
Q

What are the general characteristics of transdermal DDS?

A
  • two major designs of transdermal ‘patch’ systems
  • patch size controls dose delivered and therefore the amount of drug absorbed – patches are made in different sizes for different doses
  • patches should always be applied to clean, dry, non-hairy sites
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7
Q

What are the 2 major designs of transdermal ‘patch’ systems?

A
  • membrane-controlled (or reservoir) systems
  • matrix systems

(both systems provide controlled release of encapsulated drug over long periods of time)

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8
Q

Is the application site of patches constant?

A

yes – depending on what the system is used for

  • typically use upper back (shoulder), upper arm
  • vivelle - lower abdomen
  • minitran – chest
  • do not use lower arm or lower legs
  • if need to remove hair – clip don’t shave
  • no moisturizers or lotions
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9
Q

What are the 5 major components of membrane-controlled transdermal DDS?

A
  • outer backing – impermeable metal/plastic laminate
  • drug reservoir
  • rate controlling membrane
  • adhesive layer
  • release liner
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10
Q

Membrane-Controlled Transdermal DDS Components

What is the purpose of the outer backing?

A

protection of the patient and the drug, and provides identification of the medication and system

  • occlusive to prevent the transmission of water vapour
  • impermeable to the penetration of drug
  • typically made of poly(ethylene) terephthalate sometimes laminated to thin metal foil
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11
Q

Membrane-Controlled Transdermal DDS Components

What is the purpose of the drug reservoir?

A

holds the drug dispersion

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12
Q

Membrane-Controlled Transdermal DDS Components

What is the drug reservoir composed of?

A

composed of solid drug particles dispersed in:

  • viscous liquid silicon fluid (Transderm Nitro)
  • gel – poly(acrylic acid) (Estraderm)
  • solid polymer (polyisobutylene) (Transderm V)
  • may contain a penetration enhancer (ethanol or surfactant)
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13
Q

Membrane-Controlled Transdermal DDS Components

What is the purpose of the rate-controlling membrane?

A

controls the diffusion rate of drug from the reservoir into the skin – drug release control

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14
Q

Membrane-Controlled Transdermal DDS Components

What is the rate-controlling membrane typically composed of?

A
  • poly(ethylene) (Nicoderm)
  • ethylene-co-vinyl acetate (EVA) (Estraderm)
  • EVA + other polymers
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15
Q

Membrane-Controlled Transdermal DDS Components

What is the purpose of the adhesive?

A

allows the patch to remain in place

  • must be permeable to the drug and be biocompatible
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16
Q

Membrane-Controlled Transdermal DDS Components

What is the adhesive typically composed of?

A
  • poly(acrylates)
  • silicones (Duragesic)
  • poly(isobutylene) (Transderm V)
17
Q

Membrane-Controlled Transdermal DDS Components

What is the purpose of the release liner?

A

to prevent the adhesive from sticking to
packaging or unwanted sites prior to use

  • is removed and discarded prior to application
  • mmust be impermeable to the drug and release easily from adhesive
18
Q

Membrane-Controlled Transdermal DDS Components

What is the release liner typically composed of?

A

polyester or polypropylene coated with fluoropolymer (non-stick)

19
Q

Drug Release from Membrane Controlled Transdermal DDS

A

Fick’s Law of Diffusion

20
Q

What are the major components of matrix (monolithic) transdermal DDS? (3)

A
  • outer backing – impermeable metal/plastic laminate
  • drug-loaded matrix
  • two general designs with regards to the adhesive layer – may be a rim around the drug matrix or the matrix itself may be adhesive
21
Q

What are the characteristics of matrix (monolithic) transdermal DDS? (3)

A
  • no rate-controlling membrane – skin controls the rate of drug absorption, useful for drugs with a wide therapeutic index
  • thinner and smaller than membrane-controlled devices
  • release is not constant (zero order) but is controlled and predictable (first order)
22
Q

What are some examples of matrix (monolithic) transdermal DDS?

A
  • Nitrodur (nitroglycerin)
  • Minitran (nitroglycerin)
  • Climera (estradiol)
  • Estradot (estradiol)
  • Oxytrol (oxybutynin)
  • Ortho Evra (norgertromin/ethinyl estradiol)
23
Q

What are the disadvantages of transdermal DDS? (6)

A
  • lack of dosing flexibility
  • dosing fluctuations
  • drug must have high biological activity
  • only a few suitable drugs
  • adhesion problems
  • rate-controlling membrane technology is expensive
24
Q

Would you recommend that a patient cut a transdermal patch to adjust the dose?

A

–

25
Q

What is the stratum corneum?

A

primary barrier for absorption of drugs through the skin

  • major limitation for types of drugs selected for TDD
26
Q

Methods are needed that can overcome the barrier of the stratum corneum. What should they be able to do? (3)

A
  • increase skin permeability reversibly
  • provide an added driving force for transport (ie. better than what is being used currently)
  • avoid damage to deeper, living tissue
27
Q

What technologies have been developed?

A
  • iontophoresis
  • spray on
  • microneedles
28
Q

What is iontophoresis?

A

movement of drugs through the skin using an electrical current

  • charged drugs are moved via electrophoresis
  • weakly charged drugs or neutral drugs move by electroosmotic flow of water generated by the movement of positive ions (Na+)
  • allows for change in the delivery rate by changing the current (may be patient-controlled)
29
Q

What is iontophoresis limited by?

A

skin irritation and pain

30
Q

What is iontophoresis currently used for?

A

to rapidly administer lidocaine

31
Q

What are microneedles?

A
  • size is small (300 μm) – they do not reach nerves in the dermis and are ‘painless’ (pressure feeling)
  • single or arrays of microneedles – epidermis/dermis
  • hollow microneedles deliver drugs from a reservoir
  • solid microneedles are coated with the drug
32
Q

What are microneedles most promising for?

A

vaccination – because they are often dose-sparing over IM injections

  • no training required
  • mass distribution
  • painless
  • patient administered
33
Q

What are the type of microneedles? (4)

A
  • solid MN
  • coated MN
  • dissolving MN
  • hollow MN
34
Q

What are solid microneedles?

A

coated with the drug

35
Q

What are some applications of microneedles?

A
  • injection (cosmetics) – botox, tattoos
  • injection (biomedical) – vaccines, allergy tests, insulin, human GLP-1 analog for type 2 diabetes treatment
  • extraction – continuous glucose monitoring, blood sampling, interstitial fluid extraction and analysis for therapeutic drug monitoring
36
Q

What are the components of spray-on systems? (3)

A
  • solution containing the drug
  • volatile solvent
  • chemical penetration enhancer
37
Q

What do transdermal spray-ons do?

A

promote drug delivery via the complex interplay between solvent evaporation and drug–solvent penetration

38
Q

What are the advantages of transdermal spray-ons?

A
  • applied to a defined surface area
  • cost-effective
  • flexible dose administration
  • less irritation
  • aesthetically acceptable
39
Q

What are the disadvantages of transdermal spray-ons?

A
  • 50% of the drug remains on the surface
  • drug transfer via skin contact

PHRM 100 – PDD (14 decks)

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