Final answer:
The abbreviation 'AC' is used on prescriptions to indicate that a medication should be taken orally before meals. It is a directive that can affect the absorption and effectiveness of certain medications.
Step-by-step explanation:
The abbreviation used in a prescription to indicate that a medication should be taken orally before meals is c) AC. The abbreviation 'AC' stands for ante cibum, which is Latin for 'before meals'. This is an important instruction as the absorption of certain medications can be affected by food, thus taking them before meals can ensure that they work effectively.
When Barbara was prescribed amoxicillin for pneumonia, she would have been given directions for when to take the medication, which might include taking it 'AC.' In her follow-up visit, this directive might be scrutinized if her recovery has not progressed as expected, to ensure she's been taking the medication as instructed.