RxContextRx

Which abbreviations get confused in medication instructions?

The classics are short abbreviations that look like another one with a different meaning: "QD" read as "QID", "IU" read as "IV", "U" read as a zero or a four, and ear abbreviations read as eye ones. ISMP, the Institute for Safe Medication Practices, lists these as error-prone and says they should not be used.

These are textbook examples from ISMP's published list, not ContextRx findings. Our own cases are on the case index.

Watch for these

From ISMP's List of Error-Prone Abbreviations, Symbols, and Dose Designations (2024):

  • "QD" (every day) has been mistaken for "QID" (four times a day). ISMP says to write daily.
  • "IU" (international unit) has been mistaken for "IV" (intravenous) or for the number 10. ISMP says to write units.
  • "U" (unit) has been mistaken for a zero or a four, causing a tenfold overdose or more, or for "cc". ISMP says to write units.
  • "cc" (cubic centimeters) has been mistaken for "u" (units).
  • "AD", "AS" and "AU" (right, left and each ear) get mistaken for "OD", "OS" and "OU" (right, left and each eye), and the other way round. ISMP says to write out right ear, left eye and so on.
  • "SSRI" and "SSI", shorthand for a sliding-scale dosing order, have been mistaken for an antidepressant class and for a different named solution. ISMP says to spell out the sliding-scale order in full.
  • "D/C" can mean discharge or discontinue, and ISMP notes medicines have been stopped too early when D/C meant discharge. ISMP says to write discharge, or discontinue or stop.

Why this matters for label writers

These are abbreviation swaps, not wrong words. They're close relatives of the correctly spelled wrong word because each abbreviation is valid, so nothing flags it, and the reader has to work out the meaning. Our view: the fix is the same as ISMP's: spell it out where it matters. For real word pairs on published labels, see confusable words in drug labeling.

Sources

Last reviewed: October 14, 2026

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FAQ

What abbreviations are most often confused in medication instructions?

ISMP's error-prone list includes QD read as QID, IU read as IV, U read as a zero or four, SSRI or SSI for a sliding-scale dosing order, and ear versus eye abbreviations.

What does ISMP recommend instead of error-prone abbreviations?

Writing the full word, such as daily, units, or right ear.

Are these ContextRx findings?

No. They're textbook examples from ISMP's published list. Our own cases are on the case index.