Toxicity testing of polymer materials for dialysis equipment: reconsidering in vivo testing

The rationale for preclinical testing of plastic materials for medical devices is the protection of patients from leachable toxic substances. A controversial and costly part of this testing is the use of animal in vivo procedures. The objective of the present study was to analyse the importance of in vivo tests in relation to the decision to approve or not to approve materials for use. A total of 1044 plastic materials were analysed by employing chemical, in vitro and in vivo tests: 5708 in vivo tests were performed. In only one out of 2650 systemic injection tests on mice did a material fail. As that material also failed in chemical tests, the systemic injection test had no influence on the decision not to approve the material. Intradermal irritation (2644 tests), implantation (398 tests) and sensitivity (11 tests) procedures on rabbits and guinea-pigs were the other in vivo tests. However, in all except three cases, the same decision on whether or not to use a material would have been reached without any of these in vivo tests. Thus, little security appears to be gained from the in vivo tests, and abandoning them would save resources, probably without any additional risk.