It seems that the National Anti-Vivisection Society (NAVS) aren’t up-to-date, even on their latest press release where the Notes to Editors contains information that has been proved wrong many, many, MANY times; including being deemed erroneous by an independent bodies such the Advertising Standards Authority.

For ‘Examples of species differences’, NAVS uses the (rotten) chestnuts that:

morphine calms people & rats but excites cats and mice;
penicillin is a useful antibiotic for people but kills guinea pigs

Sigh.  These fallacies have been debunked so many times that it’s not even funny – just wearying – that they keep being trotted out.

What the hell, let’s go one more time:

Morphine:
cats and mice given (low) doses comparable with those given to humans are sedated ie ‘calmed’… conversely, humans who overdose on morphine become ‘excited’.

To make it even worse, NAVS was censured by the ASA way back in 1993 on the morphine claim (See RDS’ dossier on scientific validity complaints (p.20, complaint 3) showing ASA rulings against antiviv/ AR groups).

Penicillin:
in guinea pigs actually works very similarly to the way it does in humans. Again, the toxic effect is dose related and is apparent at high doses or in long-term treatment:

[Its] effect in the guinea-pig is due to an indirect effect. This is the conclusion of a study which showed that bacteria normally present in the guinea-pig intestine are sensitive to penicillin. Thus, after penicillin, all these bacteria disappear and are replaced by far greater numbers of other types of bacteria. Thus infection leads to absorption of toxins and death from blood poisoning. Thus it appears that the guinea pig, far from being strikingly different from humans, is in fact similar to the many patients who develop inflammation of the colon (colitis) when they take penicillin.
RDS website, The truth about penicillin

See these original sources of information if the RDS’ word isn’t good enough for you (Jarrod Bailey take note, sourcing info to someone other than yourself is a good move):
Med Microbiol Immunol (Berl). 1981;169(3):187-96 - giving penicillin to guinea pigs selectively kills bacteria in their gut, allowing Clostridium difficile to overgrow and produce a toxin that can kill.
Health Protection Agency - giving penicillin to people selectively kills bacteria in their gut, allowing Clostridium difficile to overgrow and produce a toxin that can kill (note the sense of déjà vu).
Clin Microbiol Infect. 2006 Feb;12(2):184-6 *bonus info on alternatives* - advanced alternative techniques mean guinea pigs don’t need to be used to test for C. difficile

If NAVS can’t be bothered to update these lies (pointed out to them – 13 years ago and counting – by independent bodies so no rigorous research required), it’s no surprise that the rest of their information is badly researched and scientifically inaccurate.