# Error-Prone Abbreviations to Avoid on Prescriptions (ISMP List): qd, qod, SQ, U, IU, µg, cc, OD/AD

> Abbreviations, symbols and dose designations that ISMP lists as error-prone — qd, qod, SQ, U, IU, µg, cc, OD/OS/OU vs AD/AS/AU, BIW, TIW, D/C, trailing zeros — what they are mistaken for and what to write instead.

- Source page: https://wevet.in/vet-abbreviations/error-prone-abbreviations/
- Type: Abbreviations
- Publisher: WeVet
- Updated: 2026-11-01
- Audience: veterinarians and veterinary students

The Institute for Safe Medication Practices (ISMP) keeps a list of abbreviations, symbols and dose designations that have been misread in medication orders, with what each was mistaken for and what to write instead [1]. Several of them — q.d., qod, SQ, OD and AD — also appear in veterinary abbreviation lists [2][3].

## Error-prone abbreviations

| Abbreviation | Intended meaning | Mistaken as → write instead |
|---|---|---|
| µg | Microgram [1] | Mistaken as mg → use mcg [1] |
| cc | Cubic centimetres [1] | Mistaken as u (units) → use mL [1] |
| IU | International unit(s) [1] | Mistaken as IV or the number 10 → use unit(s) [1] |
| U, u | Unit(s) [1] | Mistaken as zero or the number 4 (4U seen as 40), or as cc → use unit(s) [1] |
| qd, QD, q.d. | Every day [1] | Mistaken as q.i.d. → use daily [1] |
| qod, QOD, q.o.d. | Every other day [1] | Mistaken as qd (daily) or qid (four times daily) → use every other day [1] |
| OD (once daily) | Once daily [1] | Mistaken as right eye (OD, oculus dexter) → use daily [1] |
| OD, OS, OU | Right eye, left eye, each eye [1] | Mistaken as AD, AS, AU → use right eye, left eye or each eye [1] |
| AD, AS, AU | Right ear, left ear, each ear [1] | Mistaken as OD, OS, OU → use right ear, left ear or each ear [1] |
| SC, SQ, sq, sub q | Subcutaneous(ly) [1] | SC mistaken as SL (sublingual); SQ as "5 every"; the q in sub q as "every" → use SUBQ (capitals, no spaces or periods) or subcutaneous(ly) [1] |
| BIW, biw | 2 times a week [1] | Mistaken as 2 times a day → use 2 times weekly [1] |
| TIW, tiw | 3 times a week [1] | Mistaken as 3 times a day or twice in a week → use 3 times weekly [1] |
| D/C | Discharge or discontinue [1] | Misinterpreted as discontinued → write discharge, discontinue or stop [1] |
| IN | Intranasal [1] | Mistaken as IM or IV → use intranasal [1] |
| IJ | Injection [1] | Mistaken as IV or intrajugular → use injection [1] |
| 1.0 mg (trailing zero) | 1 mg [1] | Mistaken as 10 mg if the decimal point is not seen → do not use trailing zeros for whole-number doses [1] |
| .5 mg (naked decimal) | 0.5 mg [1] | Mistaken as 5 mg if the decimal point is not seen → use a leading zero before a decimal point when the dose is less than one measurement unit [1] |
| > and < | More than and less than [1] | Mistaken as the opposite; < misread as 4 → write more than or less than [1] |
| @ | At [1] | Mistaken as the number 2 → use at [1] |
| & | And [1] | Mistaken as the number 2 → use and [1] |
| + | Plus or and [1] | Mistaken as the number 4 → use plus, and, or in addition to [1] |
| ° (hour) | Hour [1] | Mistaken as a zero (q2° seen as q20) → use hr, h or hour [1] |

## Frequently asked questions

### Why is "qd" considered dangerous?

ISMP reports that qd is mistaken as q.i.d. (four times daily); write "daily" instead [1].

### What should be written instead of "U" for units?

The word "unit(s)" — U is mistaken as zero or the number 4, so 4U can be read as 40 [1].

### Why avoid trailing zeros?

1.0 mg is mistaken as 10 mg if the decimal point is not seen [1].

## References

[1] ISMP List of Error-Prone Abbreviations, Symbols, and Dose Designations — Institute for Safe Medication Practices (ISMP) (2024). https://online.ecri.org/hubfs/ISMP/Resources/ISMP_ErrorProneAbbreviation_List.pdf
[2] Veterinary Abbreviations & Acronyms Guide — University of Illinois — Veterinary Medicine Library. https://www.library.illinois.edu/vex/vetabbrev
[3] Accepted Veterinary Medical Shorthand and Acronyms — University of Michigan research website (az.research.umich.edu) (last updated 2016). https://az.research.umich.edu/sites/default/files/media/embedded/Accepted%20Veterinary%20Medical%20Shorthand%20and%20Acronyms.pdf

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Numbers in [brackets] cite the references above. For veterinary professionals. Information supports — never replaces — clinical judgement; always check the current product label and local regulations.
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