Is penicillin toxic to guinea pigs?
No, not at doses equivalent to those taken by people. Early studies showed that very large doses of impure penicillin caused toxic effects in guinea pigs, hence the animal rights claim that penicillin is toxic to guinea pigs. In fact, the toxic effects seen in guinea pigs after very large doses are very similar to an effect sometimes seen in patients on long-term penicillin, so guinea pigs and humans react in very similar ways.
