Intracutaneous reactivity test

Two commonly used in vivo, nonclinical tests that are used to evaluate irritation are the intracutaneous and primary skin irritation tests. The intracutaneous reactivity test is aggressive in that it makes use of extracts prepared under exaggerated conditions and places them directly into the skin of test animals, thereby maximizing the chance of finding irritants chemicals if they are present. The primary skin irritation test is less aggressive in that portions of the test material itself are simply placed on the shaved back of albino rabbits. If applicable other irritation tests such as oral, rectal, penile, and vaginal irritation tests are described in annex D of the standard as complements to, not replacements for the primary tests. They are considered relevant for medical devices intended to be applied to those respective mucosal areas of the body. 

The modified polymer beads [347] passed all of the standard battery of biocompatibility tests required by the International Organization for Standardization guidelines (ISO 10993). The tests included in vitro coagulation tests (plasma recalcification time), hemolysis study (extraction method), cytotoxicity study using the ISO elution method, etc. In in vivo experiments, extracts of the polymer beads did not elicit pyrogenic irritation or sensitization reactions in laboratory animals (acute systematic toxicity study in the mouse, acute intracutaneous reactivity study in the rabbit, rabbit pyrogen study). 

The US Pharmacopeia (USP) describes the in vitro and in vivo biological reactivity tests of elastomerics, plastics, and other polymeric materials with direct or indirect patient contact. Agar diffusion, direct contact, and elution tests are in vitro tests using L-929 mammahan fibroblast cehs. Systemic injection, intracutaneous, and implantahon tests are in vivo tests. A brief summary of these tests is listed in Table 20.4. For detailed informahon, readers are referred to USP chapters 87 and 88. 

Exposiue to or contact with even minute amounts of potential leachables in medical devices or biomaterials can result in allergic or sensitization reactions. Sensitization tests estimate the potential for contact sensitization of medical devices, materials, and/or their extracts, are usually carried out in guinea pigs, and should reflect the intended route (skin, eye, mucosa) and nature, degree, frequency, duration, and conditions of exposure of the biomaterial in its intended clinical use. Emphasis is placed on utilizing extracts of the biomaterials to determine the irritant effects of potential leachables. Intracutaneous (intradermai) reactivity tests determine the localized reaction of tissue to extracts of medical devices, biomaterials, or pros-theses in the final product form. Irritation and intracutaneous tests may be applicable where determination of irritation by... 

Irritation and intracutaneous reactivity, such as USP/ISO intracutaneous reactivity, ISO mucosal irritation (vaginal, rectal, oral), ocular irritation test set by the ISO and the Organisation for Economic Co-operation and Development (OECD), intraocular irritation, and ISO/ Environmental Protection Agency (EPA)/OECD dermal irritation. 

Irritation testing determines whether the test article will cause irritation to the relevant tissue. Various models are available to test an article, the most common being the intracutaneous reactivity study (IC). In this test, extracts are typically used to inject five 0.2 mL boluses per extract into the skin of rabbits. The injections are usually the size of a mosquito bite. The skin sample area is observed every 24 h for 72 h following the injections and is scored for erythema and edema. The test sites are compared with control sites, and in order for the test article to pass, the difference of the average scores cannot exceed 1. The IC test can also be used with the test article directly if it is small enough to pass through a needle. 

P4HB and P3HB-4HB have been evaluated in preclinical tests reconunended by the FDA for medical devices. These tests include cytotoxicity, sensitization, irritation and intracutaneous reactivity, hemocompatibility, and implantation. Thus for example, P4HB films and sutures were subjected to a complete series of biocompatibility test protocols that were performed in accordance with the FDA s GLP regulations as set forth in 21 CFR, part 58, as well as ISO 10993-1. The test results confirmed that P4HB is nontoxic and biocompatible (Martin DP, personal communication). 

The extract dilution type of cell culture assay requires a solvent extraction of the biomaterial under consideration and testing of this extract, most commonly at various dilutions, for evidence of cytotoxicity and cellular interaction. This type of cell culture assay finds its most common use in providing information for regulatory compliance. As identified in the preceding Materials for Medical Devices section and in Table 1, low-molecular-weight extractables are of concern regarding biocompatibility. The extraction assay, carried out with a series of solvents that are hydrophilic and hydrophobic, permits examination of the potential cytotoxicity of extracts and the identification of materials within a biomaterial that may be cytotoxic. These types of assays ultimately permit identification and characterization of cytotoxic materials within biomaterials or the lack of cytotoxicity, as well as providing correlation with in vivo assays such as sensitization, irritation, intracutaneous (intradermal) reactivity, and other tests where the in vivo injection of extracts is required. 

---