William Hyman: The FDA’s Scrutiny of Materials

An ongoing issue in the use of materials for implanted or tissue-contacting medical devices is how specifically the material should be identified. I addressed this here earlier in the unexpected context of ventilator breathing tubes. As I noted then, the FDA seemed to be asserting a requirement for stricter testing of the gas contacting materials, including better material characterization. While these tubes are not implanted, gas that passes through the breathing tube may interact with the tube material in a way that is potentially harmful to the patient.

Now, the FDA’s scrutiny of materials comes in the form of a guidance document called Implanted Blood Access Devices for Hemodialysis.  This document provides recommendations for complying with the “special controls” for 510(k) submissions that are applicable to devices reclassified from pre-amendment Class III to Class II. The Federal Register notice of these special controls was published in July 2014. While this document, like all guidance documents from the FDA, does not establish legally enforceable responsibilities, it would be interesting to submit a 510(k) that deviated from the agency’s recommendations.

The guidance first recommends the identification of all materials used to make the components of the hemodialysis catheter, “including any colorants (inks, dyes, markings, etc.), plasticizers (including di-(2-Ethylhexyl) phthalate or DEHP), lubricants, mold release agents, additives, or coatings.” Thus, just the chemical name of the polymer would not be enough as compared with specifying the base polymer and all of the additional components that make up a modern plastic.

The document also calls for the identification of the supplier, material name, and material designation number. I was told by the FDA that material designation number means the particular material suppliers catalog number. This is more specific than, for example, a polymer’s CSA number, which just tells you the generic base polymer but not the full specifications, additives or supplier. What is not addressed is how tight the supplier’s specifications and quality control needs to be so that a particular material from a particular supplier is sufficiently identical from one purchase to the next. This can be an issue when the supplier’s stated intended use for the material is for relatively low-demand applications (e.g., carpet backing) as compared to implantable medical devices.

The guidance also addresses assessment requirements when a material is not “the same” as that of a predicate device. Here, “the same” might mean as identified above in all its details, including a specific material from a particular supplier. When the material is not the same, a substantial equivalent argument can still be made when adequately supported by testing.

This device category includes catheters that pass through the skin and which must be disinfected during use. What disinfectants are or are not permissible has been a clinical challenge in part because of variations in materials, disinfection agents, and the inconsistent nature of manufacturer recommendations. For example, current labeling may have fairly generic “do not use xxx” warnings that are not as useful as saying what should be used. Testing here must—to the degree that a guidance document creates a “must”—include chemical tolerance of the device to repeated exposure to commonly used disinfection agents with such testing simulating the actual clinical use. The guidance also calls for any contraindicated disinfecting agents to be identified by printing a warning directly on the catheter. This would be particular helpful in clinical settings where different patients have different catheters with different requirements. Alternatively, contraindicated disinfecting agents must be identified by a label affixed to the patient’s medical record and with written instructions provided directly to the patient and provider.

An interesting aspect of a guidance document addressing future 510(k) contents is that the requirements (or recommendations) do not apply to any devices that have already been cleared and for sale.

William Hyman, ScD, is professor emeritus of biomedical engineering at Texas A&M University. He now lives in New York where he is adjunct professor of biomedical engineering at The Cooper Union.

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