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Medical Devices


Background

Phthalates have played a key role in health care since the 1950s, when polyvinyl chloride (PVC) made flexible by the addition of a phthalate, DEHP, revolutionized the task of storing and delivering whole blood to the military and to patients in need of transfusions. Today, flexible PVC is a vital part of the medical scene. Because it is clear, strong, flexible, easily sterilized, and resists kinking, it is a very popular choice for most medical tubing, whether for patients undergoing dialysis or those needing intravenous fluids and medicine.

The Issue

Studies have shown that when pregnant rodents were fed very high doses of DEHP, there were some negative effects on the development of the reproductive systems of male offspring. The Food and Drug Administration (FDA) has pointed out that "there are no human studies to date that show such effects." Nevertheless, the FDA conducted a "safety assessment" of DEHP in medical devices, which was completed in 2001. The purpose of the safety assessment was to review whether the small amount of DEHP that migrates out of the vinyl could pose a potential health risk. One of FDA's jobs is to regulate medical devices for their safety and effectiveness.

The Evidence

In its safety assessment, FDA set a "Tolerable Intake" (TI) level for human exposure to DEHP from medical devices. The FDA started with the rat "no-effect" level—the biggest dose given to the animals that did not affect them. Then the agency divided that dose level by 100, which is the FDA's standard way to build a large extra safety factor into its TI levels for humans. Still, the FDA had some concerns and issued a "Consumer Update" stating that its "greatest concern would be for very young male infants who are critically ill and have prolonged exposure to multiple devices containing DEHP." It noted, however, that "DEHP-containing devices have been used on newborn babies for many years without apparent ill effect, although studies have not been conducted which would rule out effects on humans." The procedure of most concern to the FDA is called ECMO, for Extra-Corporeal Membrane Oxygenation, in which the blood of infants is oxygenated using equipment that involves exposure of the blood to relatively large amounts of PVC tubing. (A 2003 study of twelve adolescent males who received ECMO treatments as infants showed no effects on their reproductive development.) The FDA's 2001 safety assessment expressed little concern for adults receiving medical treatments, such as intravenous solutions or dialysis.

The FDA also has provided a Public Health Notification to health professionals. It recommends consideration of alternative materials when procedures with relatively high exposure potential are to be conducted on sensitive persons such as male newborns. But it leaves it to medical practitioners to balance the known benefits of PVC containing DEHP against the possible risks. The FDA states: "Most importantly, you should not avoid the procedures cited above simply because of the possibility of health risks associated with DEHP exposure. The risk of not doing a needed procedure is far greater than the risk associated with exposure to DEHP."

The scientific concerns about possible risks are based primarily on the effects seen in rodents. But tests on primates, which are generally considered to be much better predictors of effects of DEHP in humans than rodents, demonstrate that primates are much less susceptible to effects from DEHP than rodents. A study reported to the Society of Toxicology in March, 2003, showed that male juvenile monkeys fed high doses of DEHP from weaning until they matured sexually experienced no negative effects on their reproductive organs, suggesting that effects on rodents may not be relevant to humans.

In addition, the FDA and other countries' regulatory agencies that have approved DEHP-plasticized PVC for use in medical devices make the point that substitutes may expose patients to hazards not present with devices made with DEHP. Any alternative to DEHP in vinyl will have to undergo scientific scrutiny and receive approval from the FDA before it can be used in medical devices.


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