What symptom could indicate an adverse reaction to antibiotics?

Diarrhea or rash is a significant indication of an adverse reaction to antibiotics. Many antibiotics can disrupt the natural flora of the gut, leading to antibiotic-associated diarrhea, which can range from mild to severe. The disruption can also allow for the overgrowth of pathogenic organisms such as Clostridium difficile, which can lead to more serious complications. Additionally, rashes can indicate hypersensitivity or allergic reactions to the antibiotic, which may manifest as simple rashes or escalate to more severe conditions such as Stevens-Johnson syndrome. Such symptoms require careful monitoring and potentially prompt intervention, making them key signs of adverse reactions to antibiotic therapy.