Final answer:
The abbreviation 'ac' is used in prescriptions to indicate that a medication should be taken orally, before meals. It stems from the Latin 'ante cibum' and is crucial for the drug's effective absorption and action.
Step-by-step explanation:
The abbreviation used in a prescription to indicate that a medication should be taken orally, before meals is 'ac', which is derived from the Latin term 'ante cibum'. This instruction is important as it can affect the drug's absorption and efficacy. In contrast, 'pc' indicates that the medication should be taken after meals. Prescribing information such as 'ac' helps ensure that the patient takes medicine in a way that maximizes its therapeutic effect while minimizing potential side effects or interactions with food.