Final answer:
Skin rashes caused by penicillins may not always be due to an allergic reaction; for instance, ampicillin or amoxicillin can induce rashes without an allergy, often in viral infections. Penny's rash, initially suspected to be allergic eczema, was eventually linked to Pseudomonas aeruginosa infection, which is not effectively treated with penicillin due to resistance.
Step-by-step explanation:
Skin Rashes Caused by Penicillins
While it is true that up to 5% of the population can have an allergic reaction to penicillins, it is also possible for some penicillin medications to cause skin rashes that are not due to an allergic mechanism. An example of a non-allergic skin rash could be a reaction to ampicillin or amoxicillin; these antibiotics are known to cause rashes even in the absence of an allergy, particularly when used in patients with viral infections like infectious mononucleosis. In such scenarios, the rash is not an indication of an allergy to penicillin, but rather a reaction related to the viral infection itself.
For Penny, who developed a skin rash, the initial thought was an allergic eczema possibly related to a change in sunscreen, not penicillin. After further investigation, it was determined that her rash was due to Pseudomonas aeruginosa, a bacterium resistant to many antibiotics, including some penicillins. Although penicillins are effective against a variety of infections, not all rashes that coincide with their use are indicative of an allergy.