How does the oxybutynin transdermal delivery system (OXY-TDS) work? Steady Relief for Overactive Bladder

The Oxybutynin Transdermal Delivery System (OXY-TDS) is a matrix-type patch designed to deliver oxybutynin, a medication used to treat overactive bladder, through the skin for systemic absorption. The patch contains 36 mg of racemic oxybutynin and is designed to deliver 3.9 mg/day continuously over 3-4 days. It utilizes a drug-in-adhesive matrix with a permeation enhancer (triacetin) to facilitate controlled absorption through the skin, bypassing first-pass metabolism and reducing side effects like dry mouth. The patch can be applied to the abdomen, buttock, or hip, and its occlusive backing film ensures consistent drug delivery. While it is not more effective than oral forms, it offers advantages such as steady drug levels and fewer systemic side effects.

Key Points Explained:

1. Patch Design and Composition

   • The Oxybutynin Transdermal Patch is a matrix-type system consisting of:
     • A peel-off protective layer
     • An occlusive backing film
     • An adhesive layer containing oxybutynin (36 mg) and triacetin (a permeation enhancer)
   • The matrix design ensures controlled drug release, avoiding the "reservoir effect" seen in other patch types.

2. Mechanism of Delivery

   • Upon application, skin hydration softens the stratum corneum, allowing oxybutynin and triacetin to diffuse into the skin.
   • Triacetin interacts with skin lipids to modulate the drug’s diffusion rate, ensuring steady absorption.
   • The drug’s properties (357 Da molecular weight, lipophilicity, and weak base nature) make it ideal for transdermal delivery.

3. Pharmacokinetic Advantages

   • Bypasses first-pass metabolism: Unlike oral oxybutynin, the transdermal route avoids extensive liver metabolism, reducing the production of the metabolite N-desethyloxybutynin (DEO), which causes dry mouth.
   • Steady-state delivery: Releases 3.9 mg/day for 3–4 days, maintaining consistent plasma levels with twice-weekly applications.

4. Application and Flexibility

   • Can be applied to the abdomen, buttock, or hip (39 cm² patch size).
   • Bioequivalence studies confirm consistent absorption across these sites.

5. Clinical Trade-offs

   • Pros: Fewer anticholinergic side effects (e.g., dry mouth) compared to oral forms.
   • Cons: Higher cost and skin irritation (10% discontinuation rate).

6. Comparative Efficacy

   • No superior efficacy to oral formulations (immediate or extended-release).
   • Preferred for patients sensitive to oral side effects or those needing consistent dosing.

This system exemplifies how transdermal technology balances drug chemistry, patient comfort, and therapeutic outcomes—quietly advancing treatment for conditions like overactive bladder.

Summary Table:

Need a reliable transdermal delivery solution?
At Enokon, we specialize in bulk manufacturing of advanced transdermal patches, including custom formulations for pain management and systemic drug delivery. Our expertise in permeation enhancers and matrix design ensures optimal drug release and patient comfort.

Contact our team to discuss tailored R&D for your healthcare or pharma brand!