Applications and Formulation Design of Paclitaxel and Sirolimus in DCB and DES

The clinical application of paclitaxel and sirolimus requires targeted formulation design tailored to the characteristics of DCB and DES devices to fully exert the antiproliferative effects of the drugs while ensuring safety and efficacy. This article focuses on the specific application schemes of the two drugs in the two types of devices, analyzing the core points of formulation design and the logic of excipient selection.

There are significant differences in drug delivery methods and formulation design between DCB and DES, which fundamentally depend on the mechanism of action of the devices (rapid release vs. slow sustained release), while excipient systems need to be optimized to improve efficacy and safety.

1 Common Drugs and Formulations for Drug-Coated Balloons (DCB)

DCB delivers drugs rapidly to local tissue through brief contact with the vessel wall (30-60 seconds) during balloon dilation, without requiring a polymer carrier. The drug must be highly lipophilic to achieve rapid penetration and long-term retention.

① Paclitaxel (Mainstream Choice)

• Formulation characteristics: Paclitaxel is mixed with a hydrophilic matrix (e.g., iopromide X-ray contrast agent, urea) to form crystals or microparticles, promoting rapid drug release and penetration.

• Dosage range: 3-3.5 μg/mm² (e.g., SeQuent Please balloon).

• Representative products: SeQuent Please (Biotronik, paclitaxel + iopromide matrix), IN.PACT (Medtronic, paclitaxel + urea matrix).

• Advantages: Short-term high-concentration release, no polymer residue, reducing inflammatory reactions.

• Controversy: Some studies have suggested a potential long-term mortality risk with paclitaxel, but most clinical data support its safety.

② Sirolimus Derivatives (New Exploration)

• R&D background: To overcome the cytotoxicity issues of paclitaxel, recent attempts have been made to use sirolimus, everolimus, etc., in DCB.

• Technical challenges: Sirolimus has low lipophilicity, requiring improved formulations to enhance tissue retention (e.g., nanoparticle encapsulation, liposomal delivery). Additionally, issues such as drug precipitation during ultrasonic spraying and reduced efficacy due to elevated temperatures need to be addressed.

• Representative products: MagicTouch (MicroPort, China, sirolimus nanoparticle-coated balloon), Selution (MedAlliance, microencapsulated sirolimus sustained-release balloon with release lasting up to 1 month).

2 Common Drugs and Formulations for Drug-Eluting Stents (DES)

DES achieves slow drug release (over weeks to months) through a polymer carrier. The core functions of the polymer carrier are to control the drug release rate, enhance the binding force between the drug and the stent substrate, and ensure biocompatibility.

① Sirolimus and Its Derivatives (m-TOR Inhibitors, Mainstream Choice)

• Representative drugs and formulations: Sirolimus (first used in DES, e.g., Cypher stent, combined with permanent polymers such as polyvinyl alcohol), everolimus (higher lipophilicity, more uniform release, e.g., Xience stent, often used with the biodegradable polymer PLGA), zotarolimus (rapid tissue penetration, e.g., Endeavor stent, paired with phosphorylcholine polymer to reduce inflammatory reactions).

• Advantages: Strong antiproliferative effect with relatively balanced endothelial repair.

• Disadvantages: Certain delay in vascular healing, requiring long-term antiplatelet therapy.

② Paclitaxel (Microtubule Stabilizer)

• Representative product: TAXUS stent (paclitaxel combined with styrene-butadiene copolymer SIBS for slow release).

• Advantages: Rapid onset of action, significant efficacy in small vessels and long lesions.

• Disadvantages: Relatively strong cytotoxicity, potential delay in endothelial healing, slightly higher risk of late thrombosis.

3 Key Excipients in Drug Formulations

① Polymer Carriers for Drug-Eluting Stents

• Permanent polymers: Such as polyvinylidene fluoride (PVDF) and polyurethane (PU), gradually phased out due to long-term inflammatory risks.

• Biodegradable polymers: Such as poly(lactic-co-glycolic acid) (PLGA) and polylactic acid (PLLA), which gradually degrade after drug release to reduce foreign body reactions.

• Polymer-free coatings: Direct drug crystal coatings (e.g., Bio-Freedom stent), suitable for patients at high bleeding risk.

② Matrix Components for Drug-Coated Balloons

• Iopromide: Enhances drug solubility and radiopacity (e.g., SeQuent Please balloon).

• Urea/sorbitol: Forms drug crystals to control release rate (e.g., IN.PACT balloon).

• Phospholipids/liposomes: Improve sirolimus permeability and retention time, currently in the experimental stage with no finished products yet developed.

In summary, the core of applying paclitaxel and sirolimus in DCB and DES is "adapting drug properties to device release requirements". With a rational excipient system, efficacy and safety can be further optimized. As breakthroughs are made in new formulation technologies, the application scenarios of both drugs will be further expanded, supporting the innovative development of drug coatings.