USP <88> “CLASS” TESTS
The USP Class tests are a set of in-vivo „screening“ tests to characterize the basic biocompatibility of the
plastic under investigation. Six classes of plastics are defined, based on responses to a series of in vivo
tests for which extracts, materials and routes of administration are specified. The following three invivo tests make up the USP Class test set :
ACUTE SYSTEMIC TOXICITY TEST:
PURPOSE: In-vivo systemic tests evaluate the impairment or activation of a system – rather than the
impairment of individual cells or organs. In “acute” systemic toxicity tests, the test material (extract) is tested
for systemic toxic effects as a result of a single, acute exposure.
Extracts of the test material are prepared in 4 different extraction media: a Saline solution, a 1:20 Ethanol/Saline
solution, Polyethylene Glycol 400 and Cottonseed oil. Mice are injected intravenously (saline solution and 1:20
ethanol/saline solution) and intraperitoneally (Polyethylene Glycol 400 and Cottonseed oil) with the test and control
materials over 72 h. The test is considered negative if none of the animals injected with the test material shows a
greater biological reaction than animals treated with the negative control material (blank).
IRRITATION TEST - INTRACUTANEOUS INJECTION TEST
PURPOSE: The irritation tests are in-vivo screening tests to evaluate the potential of test materials – or
their extracts – to cause irritation on the exposed part of the body.
This test for intracutaneous irritation is performed to assess inflammatory reactions after applications of extracts of
the test article. Extracts of the test material are prepared in 4 different extraction media: a Saline solution, a 1:20
Ethanol/Saline solution, Polyethylene Glycol 400 and Cottonseed oil. Rabbits are injected intracutaneously with the
test and control materials and observed over a 72h period. A primary irritation index is determined based on the
defined evaluation criteria in USP<88>.
IMPLANTATION TEST:
PURPOSE: Implant studies evaluate the local pathological effects on living tissue, at both the gross and
microscopic level of a test article that is surgically implanted into an appropriate implant site.
The implantation evaluates local effects of implanted test articles on living tissue. Test and control material is
implanted for 7 days into the paravertebral muscle of Rabbits. At the end of the observation period, the area of the
tissue surrounding the center position of each implant strip will be examined macroscopically. For the USP Class
tests, No histopathology is necessary.
The Table below gives an overview of the specified screening in vivo tests per Class:
PLASTIC CLASSES
TESTS TO BE CONDUCTED
I
X
X
II
X
X
X
X
III
X
X
X
X
X
IV
X
X
X
X
X
X
X
X
V
X
X
X
X
X
X
X
X
VI
X
X
X
X
X
X
X
X
X
Extract
USP 0.9% NaCl
1:20 EtOH/NaCl
PEG 400
Cottonseed Oil
Muscle Implant
Route
Mouse
Rabbit
Mouse
Rabbit
Mouse
Rabbit
Mouse
Rabbit
Rabbit
Procedure
Systemic-Intravenous
Intracutaneous Irritation
Systemic-Intravenous
Intracutaneous Irritation
Systemic-Intraperitoneal
Intracutaneous Irritation
Systemic-Intraperitoneal
Intracutaneous Irritation
Intramuscular
(7 day, no Histopathology)
Standard Extraction Conditions are : 50°C/72h - 70°C/24h – 121°C/1h