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The third approach uses skin delivery for systemic treatment. For example, transdermal
therapeutic systems provide systemic therapy for conditions such as motion sickness, angina, and
pain

4. Advantages of TDDS

• Increased patient compliance
• Suitable for nauseated or unconscious patients
• Easy to discontinue in case of toxic effects
• Avoid first-pass metabolism
• Decrease the dose to be administered
• Decrease the unwanted side effects
• Can be used for drugs with short biological half-lives or narrow therapeutic index.
• https://www.youtube.com/watch?v=jXivmrTN9LM&t=29s

Disadvantages of TDDS

• This system is uneconomic
• The thickness of the skin changes from one site to another, from person to person, and

with age
• There is a possibility of irritation at the site of administration such as itching, erythema,

and local oedema that may be caused by the drug
• Drugs of large molecular size cannot be developed as TDDS
• TDDS cannot deliver ionic drugs
• Poor skin permeability limits the number of drugs that can be delivered in this manner

5. Factors affecting permeation of transdermal drug delivery

A. Physiological factors: (7 main factors)
• Skin age: skin hydration and enzymatic activity decreases with age.

Children are more susceptible to the toxic effects of drugs and chemicals, partly because of their
greater surface area per unit of body weight.

• Anatomical location: the order of absorption is decreasing as follows: -------------------------
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