Plasticisers in medical applications

Most medical devices made from PVC use plasticisers to give the flexibility that makes the material so appropriate for use. The main plasticiser types are known as phthalates. These are a group of colourless, odourless and, in the presence of oxygen, readily biodegradable liquids. In addition to their use in flexible PVC, phthalates also have a range of other uses including paints, rubber products, adhesives and some cosmetics.

One of the most important phthalates by tonnage is DEHP, which is currently the only listed plasticiser recommended by the European Pharmacopoeia as the substance of choice for softening disposable medical items, blood bags and tubing.

With regard to safety, over the last 50 years there have been five to seven billion patient-days of short-term exposure and one to two billion days of long-term exposure to medical devices plasticised with the phthalate DEHP. It is a fact that during patient treatment human exposure to phthalates cannot be excluded, but it is important to note that the short-term toxicity of phthalates is extremely low, and that they have the specific advantage not to irritate skin or mucous membranes. The absence of any report of adverse effects in any way considered significant indicates clearly the safety of plasticised medical devices made from PVC.

When the revision of the Medical Device Directive (MDD) (1993/42/EEC) took place in 2007, DEHP was also discussed in the European Parliament. As a result of input from stakeholders, representatives of the European Commission, the EU Council of Ministers and the European Parliament reached an agreement on DEHP on 6 March 2007.

The agreement stated that in line with the essential requirements of the Medical Device Directive, “manufactures should avoid the use of substances that may possibly compromise the health of patients, in particular of substances which are carcinogenic, mutagenic or toxic to reproduction, and should, as appropriate, strive at developing alternative substances or products with a lower risk potential”. To achieve this objective the compromise agreement said that the European Commission should give a mandate to CEN, the European standard body, “to specify a specific label for phthalate-containing devices”. The objective of the labelling requirement is that the European Parliament wishes to encourage manufactures to ultimately substitute DEHP.

It is important to stress that DEHP can be substituted by a range alternative plasticisers. Some alternatives have existed for years and some new ones have been developed recently. The reason why substitution has not occurred before now is that the alternative may actually not have been tested to the same extent as DEHP; it may not function as effectively (for example the plastic may not prove to be as soft and flexible, which can be critical in performance terms); or the substitution may result in a significantly increase in the cost of devices (reducing the amount of medical treatment that is able to be offered).

Whether DEHP continues to be the preferred plasticiser or is replaced by and alternative plasticising substance where use of its use causes concern, the health care sector will continue to be able to benefit from PVC’s unique properties and benefits in the future.

It is interesting to note that there are also well known major beneficial consequences of plasticisers migration in that some plasticisers (DEHP and BTHC) actually contribute to enhanced red cell survival and therefore increased shelf-life for whole blood. This is explained by the fact that the plasticiser interacts and stabilises the red cell membrane.