BENZOYL PEROXIDE "SHORT TERM" CARCINOGENICITY TESTS

BENZOYL PEROXIDE "SHORT TERM" CARCINOGENICITY TESTS are inadequate types of studies to conclude that the OTC anti-acne drug is a possible carcinogen in humans, the Proprietary Association told FDA in a July 14 letter. "Evaluation of potential human risk, according to the OSTP [Office of Science and Technology Policy] interagency group, cannot be based solely on evidence from third tier "short term" tests," P-A said. P-A's letter to FDA is a follow-up to a July 29 meeting, in which the association, along with Rich-Vicks, met with the agency to discuss benzoyl peroxide's safety in relation to studies done on carcinogenicity and to discuss the drug's OTC monograph status. Benzoyl peroxide is currently Category I in the TFM for OTC acne products. The letter is also in response to a February 1987 review by the Expert Advisory Committee on Dermatology (EACD), convened by the Health Protection Branch of Canada's Health and Welfare Department. The EACD concluded that short term tests conducted on benzoyl peroxide show "some evidence" of carcinogenicity in animals and that therefore, the ingredient is a "potential carcinogen" in humans. P-A and the Nonprescription Drug Manufacturers Association of Canada (NDMAC) formed a study group which reviewed all the available human and animal safety data on benzoyl peroxide and compiled an extensive report. The document concludes that "benzoyl peroxide is not carcinogenic and therefore is safe for continued OTC use in the treatment of acne," P-A stated. In the letter the association requested a meeting with FDA in order to discuss the study group's findings. A July 9 executive summary of the P-A/NDMAC statement details further the reasons why evidence from short-term tests alone is not sufficient to conclude that benzoyl peroxide poses a carcinogenic risk to humans. "Experts in the field of cancer research generally agree that a scientific evaluation of carcinogenicity can be based solely upon the weight of the evidence from studies in either one of the first two tiers (human epidemology and animal carcinogenicity studies) but not solely upon evidence from third tier short term tests (including both in vitro genotoxicity tests and in vivo animal skin tumor promotion/progression tests)," the summary says. The summary continues: "These tests [short term] have not been validated for human hazard assessment by establishing a correlation between the results of the tests and actual human experience in the skin." The synopsis adds that "short term tests in laboratory animals using the the skin tumor promotion/progression model are only of value in studying the possible mechanism of action of carcinogens." The results of animal skin tumor promotion/progression studies showed that "tumor promotion activity of benzoyl peroxide is both strain specific and dependent upon the particular parameters of the individual experiment," the summary says. Animal carcinogenicity studies have "repeatedly failed to provide any evidence that benzoyl peroxide is a complete carcinogen," the study summary maintains. According to the report, one study, conducted by Kurokawa, was "initially interpreted to indicate the possibility of a positive result in Sencar mice was uncontrolled [and] is not consistent with the negative results in five other studies, which were conducted under similar circumstances and could not replicate the Kurokawa results." Also, "the principal investigator himself has questioned the results," the summary says. In light of Kurokawa's studies and others conducted by Slaga and Odukoya on tumor promotion, Rich-Vicks had a report prepared for FDA, which concluded that "benzoyl peroxide is not likely to act as an enhancer or producer of tumors in human skin" ("The Pink Sheet" Sept. 22, T&G-1). A month after EACD review, an International Agency for Research on Cancer (IARC) working group "affirmed the 1984 IARC determination that there was 'inadequate evidence' of carcinogenicity of benzoyl peroxide in both animals and humans," P-A noted in its letter. The association also pointed out that "a substantial portion of scientific evidence gathered and evaluated by the [study group] was not available to EACD during its deliberation."