SILICONE MATERIALS POLICY SHOULD BE IN EFFECT BY END OF APRIL, FDA SAYS; HIMA PREPARING SILICONE EQUIVALENCY TESTING PROPOSAL FOR SUBMISSION TO DEVICE CENTER

FDA's strategy for allowing continued marketing of implants containing new silicone materials is expected to be implemented by the end of April, according to device center staffers. FDA is developing the program in response Dow Corning's recent exit from the implant-grade silicone materials market. Under a plan outlined March 5, marketing of implants incorporating new silicone materials will continue while FDA reviews special applications demonstrating that the alternative silicone is "not substantially different" from materials previously supplied by Dow Corning ("The Gray Sheet" March 15, I&W-1). The intent of the program is to guarantee continued availability of the large numbers of implants that incorporate Dow Corning silicone materials. Before the silicone materials policy can be implemented, FDA must identify the type of testing needed to demonstrate that new materials are essentially equivalent to the original silicone materials. HIMA is working with the agency to develop testing requirements and is expected to forward a proposal on the issue to FDA by April 16. As previously announced ("The Gray Sheet" Dec. 7, I&W-10), Dow Corning stopped taking orders for implant-grade silicone materials on March 31. The firm, however, is maintaining a small supply of the silicones for use in equivalency testing by device manufacturers. Dow Corning is one of at least four companies planning to pull its raw materials for implants from the market. CDRH staffers say it is too early to decide whether the silicone materials policy should be applied to other types of materials being taken off the market. In February, DuPont announced that it would no longer produce materials such as Teflon for permanently implantable devices after Jan. 31, 1994. In addition, Dow Chemical told customers in 1989 that, after April 1995, it would discontinue sale of its Pellethane polyurethane elastomer for use in long-term implants and later recommended against use of the material in short-term implants. Dow Chemical sells Pellethane primarily for insulating pacemaker leads; the company's customers include Medtronic and Cordis. Another material withdrawal reportedly is being undertaken by Johnson & Johnson's Ethicon subsidiary, which is said to be phasing out production of its Biomer solution casting polymer. As well as creating new regulatory hurdles at FDA, the withdrawals are forcing device manufacturers to find new sources of raw materials. A number of companies could serve as suppliers of silicone, according to HIMA. In addition, several polyurethane suppliers are promoting their materials as alternatives to polymers and silicones. One company, Corvita, recently entered the implant materials market with Corethane, an elastomeric polycarbonate urethane. The company is offering its Corethane line of ether-free, aromatic biopolymers as an alternative to "older biomaterials being withdrawn by Dow Chemical, Johnson & Johnson, DuPont and Dow Corning," the company says. Corvita is seeking to license Corethane to medical device manufacturers. In conjunction with the deals, the firm will make its device master file on the product available to licensees. Several device manufacturers are testing Corethane for use as a stent coating, and pacemaker manufacturers have expressed interest in using the material as a pacer lead insulator and connector, according to Corvita. In addition to pacer and stent applications, Corethane "is an ideal biomaterial" for long-term in-dwelling catheters and temporary hemodialysis catheters, Corvita says. It also can serve "as a coating on...orthopedic implants and as a component in implantable reservoirs, pumps and valves," Corvita says in a March 31 press release. Corvita adds that its material is "biocompatible and highly resistant to biodegradation." The firm originally developed Corethane for use in its small diameter vascular grafts, which have been in clinical studies for over three years, the company says. Device and materials manufacturer PolyMedica also is positioning its polyurethane product, Chronoflex, ("The Gray Sheet" Aug. 26, 1991, p. 12) as an alternative to polyurethane and silicone raw materials being taken off the market. The company decided in late March to expand beyond agreements with Medtronic and Bard and make its Chronoflex commercially available to other device manufacturers. Under a May 1992 agreement, Medtronic was given exclusive rights to use Chronoflex in pacemaker applications. Medtronic currently is testing the material for pacer applications. Bard's vascular systems division has exclusive rights to use Chronoflex in central venous catheters, chronic vascular access catheters and infusion port systems. A third company, Vygon S.A., is studying Chronoflex in several types of catheters. The Medtronic and Bard agreements apply only to the solid, extrudable form of the material, called Chronoflex AL. PolyMedica does not have any agreements for Chronoflex AR, the liquid form of the material used in solution casting. PolyMedica says it has received over 800 inquiries from manufacturers regarding Chronoflex over the past several months and is in the process of responding to them. The company is telling prospective customers that it will supply them with Chronoflex as long as they agree not to use the material in the areas in which Medtronic and Bard own exclusive rights. Animal testing conducted by PolyMedica demonstrates that Chronoflex is biocompatible and biostable, according to the company. The firm also claims that, unlike Pellethane, Biomer, and Thermedic's Tecoflex polymer, Chronoflex resists environmental stress cracking because it is ether-free. In addition, because it is aliphatic and not aromatic, Chronoflex softens in the body more than Corethane, making it more amenable to soft tissue applications such as in-dwelling catheters, according to PolyMedica. While companies like Corvita and PolyMedica are promoting their polyurethane materials as substitutes for silicone and other polymers, several pacemaker manufacturers say they plan to continue using silicone as well as polyurethane materials. In addition to pacer leads and connectors, silicone is used in a variety of devices such as small-joint prostheses, penile implants and hydrocephalus shunts.