Medical Abbreviation AS: Ante Somnum (At Bedtime)

AS (or a.s.) derives from Latin ante somnum, meaning "before sleep" or "at bedtime."

Usage in Prescriptions

• Indicates medication should be taken at night (e.g., "1 tab PO a.s.").
• Common for sedatives, hypnotics, long-acting antihypertensives, certain statins, bisphosphonates.

Related Abbreviations

• HS (hora somni) = at bedtime (more common in US).
• QHS = every night at bedtime.
• PC (post cibum) = after meals.
• AC (ante cibum) = before meals.

Safety Note

AS can be confused with aortic stenosis (cardiology) or ankylosing spondylitis (rheumatology). Context is critical. The Joint Commission discourages ambiguous abbreviations; "HS" or "at bedtime" is preferred for clarity.