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To the Editor.—
The National Cancer Institute (NCI) has begun a long-term project of testing commonly used drugs for their possible carcinogenic effect in animals. In conducting these tests, the NCI uses a standard protocol that involves giving drugs for long periods (generally lifetime feeding) in large doses to mice, rats, and other experimental animals. The doses employed often exceed the usual human dose (on a body-weight basis) by factors of 50-, 100-, or 1,000-fold. Results of such tests have recently been released for reserpine, a common antihypertensive drug, and methapyralene, an antihistamine. Under the conditions of the NCI protocol, it has been suggested that these drugs have carcinogenic potential in animals.Even if there may be no reason to question the validity of these tests, it should be pointed out that the conditions of use in such tests bear little relation to the conditions of use in human patients.
Ballin JC. Carcinogenicity Testing of Drugs. JAMA. 1979;242(1):26–27. doi:10.1001/jama.1979.03300010018013