List of Error-Prone Abbreviations

ISMP's List of Error-Prone Abbreviations, Symbols, and Dose Designations contains abbreviations, symbols, and dose designations which have been reported through the ISMP National Medication Errors Reporting Program (ISMP MERP) as being frequently misinterpreted and involved in harmful medication errors. These abbreviations, symbols, and dose designations should never be used when communicating medical information. 

Abbreviations Intended Meaning 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” and “discontinue”
IJ Injection Mistaken as “IV” or “intrajugular” Use “injection”
IN Intranasal Mistaken as “IM” or “IV” 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., 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 or at bedtime Mistaken as “qh” (every hour) Use “nightly” or “at bedtime”
q.o.d. or QOD** 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 6 PM Mistaken as every 6 hours Use “daily at 6 PM” or “6 PM daily”
SC, SQ, sub q Subcutaneous SC mistaken as SL (sublingual); SQ mistaken as “5 every;” the “q” in “sub q” has been mistaken as “every” (e.g., 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” 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 the number 0 or 4, causing a 10-fold overdose or greater (e.g., 4U seen as “40” or 4u seen as “44”); mistaken as “cc” so dose given in volume instead of units (e.g., 4u seen as 4cc) Use “unit”
UD As directed (“ut dictum”) Mistaken as unit dose (e.g., diltiazem 125 mg IV infusion “UD” misin- terpreted as meaning to give the entire infusion as a unit [bolus] dose) Use “as directed”
Dose Designations and Other Information Intended Meaning Misinterpretation Correction
Trailing zero after decimal point (e.g., 1.0 mg)** 1 mg Mistaken as 10 mg if the decimal point is not seen Do not use trailing zeros for doses expressed in whole numbers
“Naked” decimal point (e.g., .5 mg)** 0.5 mg Mistaken as 5 mg if the decimal point is not seen Use zero before a decimal point when the dose is less than a whole unit
Abbreviations such as mg. or mL. with a period following the abbreviation mg mL The period is unnecessary and could be mistaken as the number 1 if written poorly Use mg, mL, etc. without a terminal period
Drug name and dose run together (especially problematic for drug names that end in “l” such as Inderal40 mg; Tegretol300 mg) Inderal 40 mg Tegretol 300 mg Mistaken as Inderal 140 mg Mistaken as Tegretol 1300 mg Place adequate space between the drug name, dose, and unit of measure
Numerical dose and unit of measure run together (e.g., 10mg, 100mL) 10 mg 100 mL The “m” is sometimes mistaken as a zero or two zeros, risking a 10- to 100-fold overdose Place adequate space between the dose and unit of measure
Large doses without properly placed commas (e.g., 100000 units; 1000000 units) 100,000 units 1,000,000 units 100000 has been mistaken as 10,000 or 1,000,000; 1000000 has been mistaken as 100,000 Use commas for dosing units at or above 1,000, or use words such as 100 "thousand" or 1 "million" to improve readability
Drug Name Abbreviations Intended Meaning Misinterpretation Correction
To avoid confusion, do not abbreviate drug names when communicating medical information. Examples of drug name abbreviations involved in medication errors include:
APAP acetaminophen Not recognized as acetaminophen Use complete drug name
ARA A vidarabine Mistaken as cytarabine (ARA C) Use complete drug name
AZT zidovudine (Retrovir) Mistaken as azathioprine or aztreonam Use complete drug name
CPZ Compazine (prochlorperazine) Mistaken as chlorpromazine Use complete drug name
DPT Demerol-Phenergan-Thorazine Mistaken as diphtheria-pertussis-tetanus (vaccine) Use complete drug name
DTO Diluted tincture of opium, or deodorized tincture of opium (Paregoric) Mistaken as tincture of opium Use complete drug name
HCl hydrochloric acid or hydrochloride Mistaken as potassium chloride (The “H” is misinterpreted as “K”) Use complete drug name unless expressed as a salt of a drug
HCT hydrocortisone Mistaken as hydrochlorothiazide Use complete drug name
HCTZ hydrochlorothiazide Mistaken as hydrocortisone (seen as HCT250 mg) Use complete drug name
MgSO4** magnesium sulfate Mistaken as morphine sulfate Use complete drug name
MS, MSO4** morphine sulfate Mistaken as magnesium sulfate Use complete drug name
MTX methotrexate Mistaken as mitoxantrone Use complete drug name
NoAC novel/new oral anticoagulant No anticoagulant Use complete drug name
PCA procainamide Mistaken as patient controlled analgesia Use complete drug name
PTU propylthiouracil Mistaken as mercaptopurine Use complete drug name
T3 Tylenol with codeine No. 3 Mistaken as liothyronine Use complete drug name
TAC triamcinolone Mistaken as tetracaine, Adrenalin, cocaine Use complete drug name
TNK TNKase Mistaken as “TPA” Use complete drug name
TPA or tPA tissue plasminogen activator, Activase (alteplase) Mistaken as TNKase (tenecteplase), or less often as another tissue plasminogen activator, Retavase (retaplase) Use complete drug name
ZnSO4 zinc sulfate Mistaken as morphine sulfate Use complete drug name
Stemmed Drug Names Intended Meaning Misinterpretation Correction
“Nitro” drip nitroglycerin infusion Mistaken as sodium nitroprusside infusion Use complete drug name
“Norflox” norfloxacin Mistaken as Norflex Use complete drug name
“IV Vanc” intravenous vancomycin Mistaken as Invanz Use complete drug name
Symbols Intended Meaning Misinterpretation Correction
ʓ Dram Symbol for dram mistaken as “3” Use the metric system
♏︎ Minim Symbol for minim mistaken as “mL” Use the metric system
x3d For three days Mistaken as “3 doses” Use “for three days”
> and < More than and less than Mistaken as opposite of intended; mistakenly use incorrect symbol; “< 10” mistaken as “40” Use “more than” or “less than”
/ (slash mark) Separates two doses or indicates “per” Mistaken as the number 1 (e.g., “25 units/10 units” misread as “25 units and 110” units) Use “per” rather than a slash mark to separate doses
@ At Mistaken as “2” Use “at”
& And Mistaken as “2” Use “and”
+ Plus or and Mistaken as “4” Use “and”
° Hour Mistaken as a zero (e.g., q2° seen as q 20) Use “hr,” “h,” or “hour”
Ф or ᴓ zero, null sign Mistaken as numerals 4, 6, 8, and 9 Use 0 or zero, or describe intent using whole words


**These abbreviations are 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.

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