ISMP List of Error-Prone Abbreviations, Symbols, and Dose Designations

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
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 At bedtime Mistaken as "qhr" or every hour Use "at bedtime"
qn Nightly Mistaken as "qh" (every hour) Use "nightly"
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 "6 PM nightly" 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 Strong Solution of Iodine
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"

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
No leading zero before a decimal dose (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
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
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
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
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
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
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 Meaning Intended Misinterpretation Correction
?? Dram Symbol for dram mistaken as "3" Use the metric system
?? Minim Symbol for minim mistaken as "mL"
x3d For three days Mistaken as "3 doses" Use "for three days"
> and < Greater than and less than Mistaken as opposite of intended; mistakenly use incorrect symbol; "< 10" mistaken as "40" Use "greater 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"
& or + 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"

**Abbreviations with a double asterisk are also included on the Joint Commission on Accreditation of Healthcare Organization'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. An updated list of frequently asked questions about this JCAHO requirement can be found at

Note:From "ISMP List of Error-Prone Abbreviations, Symbols, and Dose Designations," 2003,

©ISMP Medication Safety Alert! 8(24), pp. 3–4. Copyright 2003 by the Institute for Safe Medication Practices. Reprinted with permission.

Source: Estes, Mary Ellen Zator. Health Assessment and Physical Examination. 3rd ed. Clifton Park, NY: Thomson Delmar Learning, 2005. 980 pp.


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