 |
Silicones are widely utilized on drug delivery devices. For example, most implantable drug pumps incorporate a silicone septum which allows the drug reservoir to be refilled while remaining inside the body. Outside the body, silicone tubing is frequently found in peristaltic pumps which deliver drugs in accurately metered doses.
A new breed of devices, called combination products has emerged over the last decade. These products incorporate drugs or biological agents in a cured matrix. Silicone elastomers and gels exhibit properties which make them ideal candidates for the drug eluting matrix. Combination products blur the classic distinction between medical devices and bioactive pharmaceuticals. The FDA defines these products as “a product comprised of two or more regulated components, i.e., drug/device, biologic/device, drug/biologic, or drug/device/biologic, that are physically, chemically, or otherwise combined or mixed and produced as a single entity”.
Drug eluting stents are one example of a combination product and the FDA’s deliberations whether to classify and regulate the product as a drug or a device have been watched closely. The FDA’s current position is review and regulate “in accordance with the product’s primary mode of action”. That said, the “primary mode of action” of these products is often the subject of much debate.
The drugs found in combination products vary widely in terms of molecular weight and chemical structure. Also, all combination products are designed to release drugs at very specific rates. For example, in one therapy an initial drug “burst” may be desirable while for another therapy it is avoided. It’s not surprising then that the silicone component of combination products must be chosen with attention given to both the chemical structure of the drug and desired drug release rates. A one-size-fits-all approach will not work.
Considered as a group, silicones offer the flexibility to tailor polymers and elastomer systems to meet the varied requirements of combination products. First, polymers can be modified by choice of pendant groups which in turn will affect the steric characteristics of the system. Second, fillers can be added or removed or changed to further adjust drug release rates. Third, silicones offer a number of cure systems such that a drug incompatible with one system may be compatible in another.
Combination products offer advantages when compared with the more standard drug delivery devices. First, these products target drug delivery to specific localized tissue, allowing higher therapeutic doses to be delivered while minimizing systemic toxicity. Second, combination products can include biologics such as bone growth factors as well as genetically modified material and can localize these materials at the point of implant.
The development and commercialization of combination products is predicted to increase rapidly. Silicones will be integral in the growth of this field.
For the cutting edge implementation of this developing technology, I recommend consulting with the following ISSAC partner companies:Specialty Silicone Fabricators
