Error-Prone Abbreviations

Error-Prone Abbreviations


The abbreviations found in this table have been reported to the Institute for Safe Medical Practices (ISMP) through the ISMP Medication Error Reporting Program as being frequently misinterpreted and involved in harmful medication errors. These abbreviations should never be used when communicating medical information.

Abbreviations Intended
Misinterpretation Correction
µg Microgram Mistaken as “mg” Use “mcg”
AD, AS, AU Right ear, left ear, each ear Mistaken as “OD, OS, OU” (right eye, left eye, each eye) Use “right ear”, “left ear”, or “each ear”
OD, OS, OU Right eye, left eye, each eye Mistaken as “AD, AS, AU” (right ear, left ear, each ear) Use “right eye”, “left eye”, or “each eye”
BT Bedtime Mistaken as “BID” (twice daily) Use “bedtime”
cc Cubic centimeters Mistaken as “u” (units) Use “mL”
D/C Discharge or discontinue Premature discontinuation of medications if D/C (intended to mean “discharge”) has been misinterpreted as “discontinued” when followed by a list of discharge medications Use “discharge” or “discontinue”
IJ Injection Mistaken as “IV” (intravenous) or “intrajugular” Use “injection”
IN Intranasal Mistaken as “IM” (intramuscular) or “IV” (intravenous) Use “intranasal” or “NAS”
HS Half-Strength Mistaken as bedtime Use “half-strength” or “bedtime”
hs At bedtime, hours of sleep Mistaken as half-strength Use “half-strength” or “bedtime”
IU* International unit Mistaken as “IV” (intravenous) or 10 (ten) Use “units”
o.d. or OD Once daily Mistaken as “right eye” (OD-oculus dexter), leading to oral liquid medications administered in the eye Use “daily”
OJ Orange juice Mistaken as “OD or OS” (right or left eye); drugs meant to be diluted in orange juice may be given in the eye Use “orange juice”
Per os By mouth, orally The “os” can be mistaken as “left eye” (OS-oculus sinister) Use “PO”, “by mouth”, or “orally”
q.d. or QD* Every day Mistaken as “q.i.d.” (four times daily), especially if the period after the “q” or the tail of the “q” is misunderstood as an “i” Use “daily”
qhs Nightly at bedtime Mistaken as “qhr” or every hour Use “nightly”
qn Nightly at bedtime Mistaken as “qh” (every hour) Use “nightly” or “at bedtime”
q.o.d. or
Every other day Mistaken as “q.d.” (daily) or “q.i.d.” (four times daily) if the “o” is poorly written Use “every other day”
q1d Daily Mistaken as “q.i.d.” (four times daily) Use “daily”
q6PM, etc. Every evening at 6PM Mistaken as “every 6 hours” Use “daily at 6PM” or “6 PM daily”
SC Subcutaneous Mistaken as “SL” (sublingual) Use “subcut” or “subcutaneously”
SQ Subcutaneous Mistaken as “5 (five) every” Use “subcut” or “subcutaneously”
sub q Subcutaneous The “q” in “sub q” has been mistaken as “every” (eg, a heparin dose ordered “sub q 2 hours before surgery” misunderstood as every 2 hours before surgery) Use “subcut” or “subcutaneously”
ss Sliding scale (insulin) or ½ (apothecary) Mistaken as “55” Spell out “sliding scale”; use “one-half” or “½”
SSRI Sliding scale regular insulin Mistaken as selective-serotonin reuptake inhibitor Spell out “sliding scale (insulin)”
SSI Sliding scale insulin Mistaken as Strong Solution of Iodine (Lugol’s) Spell out “sliding scale (insulin)”
i/d One daily Mistaken as “tid” (three times daily) Use “1 daily”
TIW or tiw 3 times a week Mistaken as “3 times a day” or “twice in a week” Use “3 times weekly”
U or u* Unit Mistaken as 0 (zero) or 4 (four), causing a 10-fold overdose or greater (eg, 4U seen as 40 [forty] or 4u seen as 44 [forty-four]); mistaken as “cc” so dose given in volume instead of units (eg, 4u seen as 4cc) Use “unit”
UD As directed (“ut dictum”) Mistaken as unit dose (eg, diltiazem 125mg IV infusion “UD” misinterpreted as meaning to give the entire infusion as a unit [bolus] dose) Use “as directed”

*Included on The Joint Commission’s “minimum list” of dangerous abbreviations, acronyms, and symbols that must be included on an organization’s “Do Not Use” list, effective January 1, 2004. For more information visit


Source: Institute for Safe Medication Practices. Error-Prone Abbreviations, Symbols, and Dose Designations. 2017.

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(Rev. 2/2020)