Trans-dermal Drug Delivery
Transdermal drug delivery offers several important advantages over more traditional dosage forms. The steady permeation of drug across the skin allows for more consistent serum drug levels, often a goal of therapy. Intravenous infusion also achieves consistent plasma levels, but it is more invasive than trans dermal drug delivery. The lack of peaks in plasma concentration can reduce the risk of side effects. Thus, drugs that require relatively consistent plasma levels are very good candidates for trans dermal drug delivery. In addition, if toxicity were to develop from a drug administered transdermally, the effects could be limited by removing the patch. Another advantage is convenience, especially notable in patches that require only once weekly application. Such a simple dosing regimen can aid in patient adherence to drug therapy. Transdermal drug delivery can be used as an alternative route of administration to accommodate patients who cannot tolerate oral dosage forms. It is of great advantage in patients who are nauseated or unconscious. Drugs that cause gastrointestinal upset can be good candidates for transdermal delivery because this method avoids direct effects on the stomach and intestine. Drugs that are degraded by the enzymes and acids in the gastrointestinal system may also be good targets. First pass metabolism, an additional limitation to oral drug delivery,
the major disadvantages to trans dermal drug delivery is the possibility that a local irritation will develop at the site of application. Erythema, itching, and local edema can be caused by the drug, the adhesive, or other excipients in the patch formulation. For most patients, site rotation can minimize irritation. However, some patients develop severe allergic reactions to transdermal patches, and, in these cases, therapy must be discontinued.
Another significant disadvantage of trans dermal drug delivery is that the skin's low permeability limits the number of drugs that can be delivered in this manner.
Advantages
Disadvantages
Bioavailability of Transdermal Drug Delivery
the major disadvantages to trans dermal drug delivery is the possibility that a local irritation will develop at the site of application. Erythema, itching, and local edema can be caused by the drug, the adhesive, or other excipients in the patch formulation. For most patients, site rotation can minimize irritation. However, some patients develop severe allergic reactions to transdermal patches, and, in these cases, therapy must be discontinued.
Another significant disadvantage of trans dermal drug delivery is that the skin's low permeability limits the number of drugs that can be delivered in this manner.
Advantages
- Local effect
- Ease of administration
Disadvantages
- Low absorption for some drugs
- May cause allergic reactions
Bioavailability of Transdermal Drug Delivery
- Slow absorption, rate may vary.
- Increased absorption
- Transdermal delivery system is easy to use and withdraw.
- Continuous release for a specified period.
- Used for lipid-soluble drugs with low dose and low MW.
- Low metabolism.
- Some irritation by patch or drug.
- Permeability of skin variable with condition, anatomic site, age, and gender.
- Type of cream or ointment base affects drug release and absorption.