Transdermal Drug Delivery Systems Flashcards by Priyanka Bhatta

Transdermal Drug Delivery Systems (TDDS)

Facilitate the passage of therapeutic quantities of drug substances through the skin and into the general circulation for their systemic effects

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Transdermal Drug Delivery

API should migrate through the skin to the underlying blood supply without building up in the dermal layers

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Topical Drug Delivery

API should reside in the skin, which is the target organ

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Stratum Corneum

10- to 15-µm-thick layer of flat, partially desiccated nonliving tissue

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Composition of stratum corneum

~40% protein
~40% water
~20% lipid

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Lipid content

1) is concentrated in the extracellular phase of the stratum corneum and largely forms the membrane surrounding the cells
2) Because a major route of drug penetration is through the intercellular channels, the lipid component is considered an important determinant in the first step of absorption

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When does drug becomes available for absorption into the general circulation

when it reaches the vascularized dermal layer

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Advantages of TDDS

1) Bypass hepatic “first-pass” and gastrointestinal incompatibility
2) Reduce side effects due to the optimization of the blood concentration-time profile
3) Provide predictable and extended duration of activity
4) Greater patient compliance due to the elimination of multiple dosing schedules
5) Reversibility of drug delivery

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Disadvantages of TDDS

1) Only relatively potent drugs are suitable candidates

2) Contact dermatitis

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TDDS shelf life

up to 2 years

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TDDS patch size

< 40 cm2

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TDDS dose frequency

once a day to once a week

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TDDS aesthetic appeal

clear, tan, or white color

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TDDS packaging

Easy removal of release liner and minimum number of steps required to apply

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TDDS skin adhesion

Does not fall-off during dosing

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TDDS skin reactions

Nonirritating and nonsensitizing

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TDDS Drug release

Consistent pharmacokinetic and pharmacodynamic profiles over time

Factors Affecting Percutaneous Absorption ( listen to lec cap)

1) Drug concentration
2) Area of application
3) Lipophilic:Hydrophilic solubilities
4) Molecular weight
5) Skin hydration, needs to be dry
6) Skin thickness
7) Exposure time

Percutaneous Absorption Enhancers: Chemical enhancers

1) increase skin permeability by reversibly damaging or altering the physicochemical nature of the stratum corneum to reduce its diffusional resistance
2) Increased hydration of the stratum corneum
and/or
3) A change in the structure of the lipids and lipoproteins in the intercellular channels through solvent action or denaturation

Percutaneous Absorption Enhancers chemical enhancers’ selection is based on?

efficacy, low dermal toxicity and compatibility with other components

chemical enhancers example

Acetone
Azone
Dimethyl sulfoxide (DMSO)
Ethanol
Oleic acid
Polyethylene glycol
Propylene glycol
Sodium lauryl sulfate

Iontophoresis

delivery of a charged chemical compound across the skin membrane using an electrical field

Sonophoresis

high frequency ultrasound to enhance transdermal drug delivery

Monolithic systems

1) incorporate a drug matrix layer between backing and frontal layers
2) Drug is dispersed in a matrix layer composed of a polymeric material which controls the rate of drug release

Monolithic TDDS matrix preparation

Matrix may be prepared either with or without an excess of drug with regard to its equilibrium solubility and steady-state concentration gradient at the stratum corneum.

Monolithic TDDS are designed to contain

an excess of drug and thus have drug-releasing capacity beyond the time frame recommended for replacement ensuring continuous drug availability and absorption as used TDDSs are replaced on schedule with fresh ones.

Membrane-Controlled TDDS

contain a drug reservoir or pouch, a rate controlling membrane, and backing, adhesive and protective layers

How the release rate of drug through the controlling membrane remains

As long as the drug solution in the reservoir remains saturated

Why A small quantity of drug is frequently placed in the adhesive layer ?

to initiate prompt drug absorption and pharmacotherapeutic effects upon placement on the skin

If the drug is delivered to the stratum corneum at a rate less than the absorption capacity,

the device is the rate-controlling factor

If the drug is delivered to the skin area to saturation

the skin is the rate-controlling factor

Absorption

may vary with the site of application.

TDDSs should be applied to

clean, dry skin that is relatively free of hair and not oily, irritated, inflamed, broken, or callused

Use of skin lotion

should be avoided at the application site.

TDDSs should not be physically

altered by cutting.

How A TDDS should be removed from its protective package,

with care not to tear or cut into the unit.

Place at a site that will

not subject it to being rubbed off by clothing or movement

Wear for the full period stated in the product’s instructions

then remove and replace with a fresh system as directed

Cleanse hands thoroughly before and after applying a TDDS and do not

rub eyes or touch the mouth during handling of the system

if there is sensitivity or intolerance to a TDDS or if undue skin irritation results

Seek reevaluation

Used TDDS should be folded in half with the adhesive layer together and reused or not?

not to be reused