Final answer:
A possible side effect of taking antibiotics for acne is the lessened effectiveness of oral contraceptives, as well as an increased risk of a secondary yeast infection due to the disruption of normal microbial flora.
Step-by-step explanation:
When an adolescent girl is being treated with antibiotics for acne, in addition to topical applications, one possible side effect that should be noted is the lessened effectiveness of oral contraceptives.
Antibiotics can disrupt the normal microbiota, including the beneficial bacteria, which can lead to secondary infections such as a yeast infection characterized by itching, burning, and discharge as described in the scenarios provided.
The role of antibiotics is to kill the bacteria causing acne, but this can sometimes also affect the balance of normal flora in the body, leading to unintended consequences like vaginitis and digestive issues.