Transdermal Drug Delivery

Transdermal Drug Delivery: Patches

• Patches deliver medication through the epidermis, primarily for systemic effects.
• Components: occlusive backing, drug layer with polymer control, adhesive layer, and release liner.

Ideal Drugs for Transdermal Delivery

• Small size: facilitates passage through skin's interlaminar lipids.
• Lipophilic nature: dissolves in skin lipid layers.
• High potency: effective at low concentrations due to limited delivery compared to other routes (oral, injection).

Penetration Enhancers

• Purpose: increase drug permeation.
• Common enhancers: Ethanol and propylene glycol.
• Mechanism: disrupt interlaminar lipids in the stratum corneum, creating pathways for drug movement.
• Other mechanisms: altering keratin to facilitate drug release/prevent binding.

Application Site Considerations

• Adhere to manufacturer-recommended application sites.
• Skin properties vary across body regions (stratum corneum thickness, appendage density).
• Incorrect application sites affect drug absorption and therapeutic response.

Patch Size and Drug Release

• Patch size directly influences drug release over time (flux equation).
• Nitroglycerin patches: different doses achieved by varying patch size while maintaining design.

Limitations of Transdermal Patches

• Limited duration: typically 7-10 days due to occlusion.
• Occlusion effects:
  • Increased drug permeation due to enhanced skin hydration and expanded lipid lamellae.
  • Skin hydration and maceration: prolonged occlusion can lead to skin breakdown.
  • Microbial growth: occluded, moist environment favors pathogen growth.
  • Skin changes and altered permeability: occlusion-induced skin changes can alter drug permeability, potentially beneficial in some cases.

Heat and Transdermal Patch Usage

• Heat increases drug release and absorption.
• Potential dangers: excessive drug absorption and toxicity, especially with potent drugs like fentanyl.

Transdermal Patch Designs

Adhesive Matrix Patches

• Common design, adhesive as the drug matrix.
• Advantages: thin, translucent, less noticeable.
• Examples: Nitroglycerin, estradiol, fentanyl, methylphenidate, contraceptive patches, lidocaine, diclofenac.

Reservoir Patches

• Older design; drug reservoir separated from skin by a rate-controlling membrane.
• Characteristics: elevated drug reservoir, potential for leakage, zero-order release pattern.
• Example: testosterone.

Membrane-Matrix Hybrid Patches

• Combine drug matrix with a rate-controlling membrane.
• Advantages: sustained and immediate drug release.
• Drug in the adhesive matrix provides an initial burst effect.
• Examples: clonidine, scopolamine, fentanyl.

Other Advanced Drug Delivery Systems

Intravitreal Implants

• Membrane-controlled reservoir implants sutured into the vitreous humor.
• Example: fluocinolone acetonide for chronic non-infectious uveitis.
• Characteristics: non-biodegradable, 30 months of drug delivery.

Intrauterine Devices (IUDs)

• Membrane-controlled reservoir systems for extended drug release.
• Example: levonorgestrel for contraception (8 years).

Intravaginal Products

• Swellable matrix systems: Example: dinoprostone for cervical ripening.
• Vaginal rings: Flexible membrane-controlled reservoir rings.
  • Example: etonogestrel/ethinyl estradiol, estradiol.

Dental Products

• Biodegradable microsphere systems: Example: minocycline for periodontal disease.
• Mechanism: microspheres release drug locally for 21 days.

Pulmonary Drug Delivery

• Liposomal inhalation suspensions: Example: amikacin for Mycobacterium avium complex lung disease.
• Mechanism: liposomes target infection site by macrophage uptake.

Explore the fascinating world of transdermal drug delivery systems, focusing on patches and their components. This quiz covers ideal drugs for transdermal delivery, the role of penetration enhancers, and important application site considerations. Test your knowledge on how effective drug delivery through the skin can be achieved.