What is the abbreviation for 'by mouth'?

• A. p.o
• B. a.c
• C. p.c.
• D. ad lib

Answer: (A)

The route “by mouth” is indicated by p.o., from the Latin per os meaning “through the mouth.” This tells staff to have the patient swallow the medication rather than take it via injection or other routes. The other abbreviations refer to timing or usage rather than the administration route: a.c. means before meals, p.c. means after meals, and ad lib means as desired. So p.o. is the correct shorthand for oral administration.