Which abbreviation is used for 'Four times a day'?

The abbreviation 'QID' stands for 'quater in die,' which is a Latin phrase meaning 'four times a day.' This abbreviation is commonly used in medical contexts to indicate the frequency with which a medication should be taken. When a patient is prescribed a medication with 'QID,' it indicates they should take it four times within a 24-hour period, which is crucial for maintaining the therapeutic effectiveness of certain medications.

In contrast, the other options refer to different dosing schedules. 'AC' stands for 'ante cibum,' meaning 'before meals,' which specifies a timing rather than a frequency. 'Ad lib' is an abbreviation for 'ad libitum,' which indicates that something can be done as desired or at will, and does not imply a specific frequency. Lastly, 'prn' stands for 'pro re nata,' meaning 'as needed,' which indicates that a medication should be taken only when necessary, rather than on a scheduled basis. Thus, QID specifically highlights a clear frequency of four times daily.