List of Error-Prone Abbreviations

The ISMP 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) and have been misinterpreted and involved in harmful or potentially harmful medication errors. These abbreviations, symbols, and dose designations should NEVER be used when communicating medical information verbally, electronically, and/or in handwritten applications. This includes internal communications; verbal, handwritten, or electronic prescriptions; handwritten and computer-generated medication labels; drug storage bin labels; medication administration records; and screens associated with pharmacy and prescriber computer order entry systems, automated dispensing cabinets, smart infusion pumps, and other medication-related technologies. 

In the Table, error-prone abbreviations, symbols, and dose designations that are included on The Joint Commission’s “Do Not Use” list (Information Management standard IM.02.02.01) are identified with a double asterisk (**) and must be included on an organization’s “Do Not Use” list. Error-prone abbreviations, symbols, and dose designations that are relevant mostly in handwritten communications of medication information are highlighted with a dagger (†).

How to cite: Institute for Safe Medication Practices (ISMP). ISMP List of Error-Prone Abbreviations, Symbols, and Dose Designations. ISMP; 2021.

Error-Prone Abbreviations, Symbols, and Dose Designations

Intended Meaning


Best Practice

Abbreviations for Doses/Measurement Units 


Cubic centimeters

Mistaken as u (units)

Use mL


International unit(s)

Mistaken as IV (intravenous) or the number 10 

Use unit(s) 
(International units can be expressed as units alone)





Lowercase letter l mistaken as the number 1 

Use L (UPPERCASE) for liter 

Use mL (lowercase m, UPPERCASE L) for milliliter 

MM or M

M or K



Mistaken as thousand

Mistaken as million

M has been used to abbreviate both million and thousand (M is the Roman numeral for thousand)

Use million 

Use thousand

Ng or ng


Mistaken as mg

Mistaken as nasogastric

Use nanogram or nanog

U or u**


Mistaken as zero or the number 4, causing a 10-fold overdose or greater (e.g., 4U seen as 40 or 4u seen as 44)

Mistaken as cc, leading to           administering volume instead of units (e.g., 4u seen as 4cc)

Use unit(s)



Mistaken as mg

Use mcg

Abbreviations for Route of Administration


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



Mistaken as IM or IV

Use NAS (all UPPERCASE letters) or intranasal 



Mistaken as intratracheal, intratumor, intratympanic, or inhalation therapy 

Use intrathecal


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

Per os

By mouth, orally

The os was mistaken as left eye (OS, oculus sinister)

Use PO, by mouth, or orally

SC, SQ, sq, or sub q 


SC and sc mistaken as SL or sl (sublingual)

SQ mistaken as “5 every”
The q in sub q has been mistaken as “every” 

Use SUBQ (all UPPERCASE letters, without spaces or periods between letters) or subcutaneous(ly)

Abbreviations for Frequency/Instructions for Use




At bedtime, hours of sleep

Mistaken as bedtime

Mistaken as half-strength 

Use half-strength

Use HS (all UPPERCASE letters) for bedtime 

o.d. or OD

Once daily

Mistaken as right eye (OD, oculus dexter), leading to oral liquid medications administered in the eye

Use daily

Q.D., QD, q.d., or qd** 

Every day

Mistaken as q.i.d., especially if the period after the q or the tail of a handwritten q is misunderstood as the letter i

Use daily 


Nightly at bedtime

Mistaken as qhr (every hour)

Use nightly or HS for bedtime


Nightly or at bedtime

Mistaken as qh (every hour)

Use nightly or HS for bedtime

Q.O.D., QOD, q.o.d., or qod**

Every other day

Mistaken as qd (daily) or qid (four times daily), especially if the “o” is poorly written

Use every other day



Mistaken as qid (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



Sliding scale regular insulin

Sliding scale insulin

Mistaken as selective-serotonin reuptake inhibitor 

Mistaken as Strong Solution of Iodine (Lugol’s)

Use sliding scale (insulin) 

TIW or tiw

BIW or biw

3 times a week

2 times a week

Mistaken as 3 times a day or twice in a week

Mistaken as 2 times a day

Use 3 times weekly

Use 2 times weekly


As directed (ut dictum) 

Mistaken as unit dose (e.g., an order for “dilTIAZem infusion UD” was mistakenly administered as a unit [bolus] dose)

Use as directed

Miscellaneous Abbreviations Associated with Medication Use



Baby boy A (twin) 

Baby girl B (twin)

B in BBA mistaken as twin B rather than gender (boy)

B at end of BGB mistaken as gender (boy) not twin B 

When assigning identifiers to newborns, use the mother’s last name, the baby’s gender (boy or girl), and a distinguishing identifier for all multiples (e.g., Smith girl A, Smith girl B)


Discharge or discontinue

Premature discontinuation of medications when D/C (intended to mean discharge) on a medication list was misinterpreted as discontinued

Use discharge and discontinue or stop



Mistaken as IV or intrajugular

Use injection


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

Period following abbreviations (e.g., mg., mL.)†

mg or mL

Unnecessary period mistaken as the number 1, especially if written poorly

Use mg, mL, etc., without a terminal period

Drug Name Abbreviations

To prevent confusion, avoid abbreviating drug names entirely. Exceptions may be made for multi-ingredient drug formulations, including vitamins, when there are electronic drug name field space constraints; however, drug name abbreviations should NEVER be used for any medications on the ISMP List of High-Alert Medications (in Acute Care Settings, Community/Ambulatory Settings, and Long-Term Care Settings). Examples of drug name abbreviations involved in serious medication errors include:

Antiretroviral medications (e.g., DOR, TAF, TDF)

DOR: doravirine

TAF: tenofovir alafenamide

TDF: tenofovir disoproxil fumarate

DOR: Dovato (dolutegravir and lamiVUDine)

TAF: tenofovir disoproxil              fumarate

TDF: tenofovir alafenamide

Use complete drug names



Not recognized as acetaminophen

Use complete drug name



Mistaken as cytarabine (“ARA C”)

Use complete drug name


AT II: angiotensin II

AT III: antithrombin III (Thrombate III)

AT II (angiotensin II) mistaken as AT III (antithrombin III)

AT III (antithrombin III) mistaken as AT II (angiotensin II)

Use complete drug names


zidovudine (Retrovir)

Mistaken as azithromycin, azaTHIOprine, or aztreonam

Use complete drug name


Compazine (prochlorperazine)

Mistaken as chlorproMAZINE

Use complete drug name


diluted tincture of opium or deodorized tincture of opium (Paregoric)

Mistaken as tincture of opium

Use complete drug name



Mistaken as hydroCHLOROthiazide

Use complete drug name



Mistaken as hydrocortisone (e.g., seen as HCT250 mg)

Use complete drug name


magnesium sulfate

Mistaken as morphine sulfate

Use complete drug name

MS, MSO4**

morphine sulfate

Mistaken as magnesium sulfate

Use complete drug name



Mistaken as mitoXANTRONE

Use complete drug name

Na at the beginning of a drug name 
(e.g., Na bicarbonate)  

Sodium bicarbonate

Mistaken as no bicarbonate

Use complete drug name


novel/new oral anticoagulant

Mistaken as no anticoagulant

Use complete drug name



Mistaken as oxyCODONE, OxyCONTIN

Use complete drug name



Mistaken as patient-controlled analgesia

Use complete drug name


Pitocin (oxytocin)

Mistaken as Pitressin, a discontinued brand of vasopressin still referred to as PIT

Use complete drug name


prenatal vitamins

Mistaken as penicillin VK

Use complete drug name



Mistaken as Purinethol                 (mercaptopurine)

Use complete drug name


Tylenol with codeine No. 3

Mistaken as liothyronine, which is sometimes referred to as T3

Use complete drug name

TAC or tac

triamcinolone or tacrolimus

Mistaken as tetracaine, Adrenalin, and cocaine; or as Taxotere, Adriamycin, and cyclophosphamide

Use complete drug names

Avoid drug regimen or protocol acronyms that may have a dual meaning or may be confused with other common acronyms, even if defined in an order set 



Mistaken as TPA

Use complete drug name

TPA or tPA

tissue plasminogen activator, Activase (alteplase)

Mistaken as TNK (TNKase, tenecteplase), TXA (tranexamic acid), or less often as another tissue plasminogen activator, Retavase (retaplase) 

Use complete drug name


tranexamic acid

Mistaken as TPA (tissue                 plasminogen activator)

Use complete drug name


zinc sulfate

Mistaken as morphine sulfate

Use complete drug name

Stemmed/Coined Drug Names

Nitro drip

nitroglycerin infusion

Mistaken as nitroprusside infusion

Use complete drug name

IV vanc

Intravenous vancomycin

Mistaken as Invanz

Use complete drug name



Mistaken as Levophed (norepinephrine)

Use complete drug name


Neo-Synephrine, a well known but discontinued brand of phenylephrine 

Mistaken as neostigmine

Use complete drug name

Coined names for compounded products (e.g., magic mouthwash, banana bag, GI cocktail, half and half, pink lady)

Specific ingredients compounded together

Mistaken ingredients

Use complete drug/product names for all ingredients  

Coined names for compounded products should only be used if the contents are standardized and readily available for reference to prescribers, pharmacists, and nurses

Number embedded in drug name (not part of the official name) (e.g., 5-fluorouracil, 6-mercaptopurine)



Embedded number mistaken as the dose or number of tablets/capsules to be   administered

Use complete drug names, without an embedded number if the number is not part of the official drug name

Dose Designations and Other Information

1/2 tablet

Half tablet

1 or 2 tablets

Use text (half tablet) or reduced font-size fractions (½ tablet)

Doses expressed as Roman numerals (e.g., V) 


Mistaken as the designated letter (e.g., the letter V) or the wrong numeral (e.g., 10                     instead of 5)

Use only Arabic numerals (e.g., 1, 2, 3) to express doses

Lack of a leading zero before a decimal point  (e.g., .5 mg)**

0.5 mg

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 

Trailing zero after a 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

Ratio expression of a strength of a single-entity injectable drug product (e.g., EPINEPHrine 1:1,000; 1:10,000; 1:100,000) 

1:1,000: contains 1 mg/mL

1:10,000: contains 0.1 mg/mL

1:100,000: contains 0.01 mg/mL

Mistaken as the wrong strength 

Express the strength in terms of quantity per total volume (e.g., EPINEPHrine 1 mg per 10 mL) 

Exception: combination local anesthetics (e.g., lidocaine 1% and EPINEPHrine 1:100,000)

Drug name and dose run together (problematic for drug names that end in the letter l [e.g., propranolol20 mg; TEGretol300 mg]) 

propranolol 20 mg

TEGretol 300 mg

Mistaken as propranolol 120 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, 10Units)

10 mg

10 mL

The m in mg, or U in Units, has been mistaken as one or two zeros when flush against the dose (e.g., 10mg, 10Units), 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

Note: Use commas to separate digits only in the US; commas are used in place of decimal points in some other countries







Symbol for dram mistaken as the number 3 

Symbol for minim mistaken as mL

Use the metric system


Administer once

Administer for 1 day

Use explicit words (e.g., for 1 dose)

> and < 

More than and less than 

Mistaken as opposite of intended

Mistakenly have used the incorrect symbol

< mistaken as the number 4 when handwritten (e.g., <10 misread as 40)

Use more than or less than

↑ and ↓†

Increase and decrease

Mistaken as opposite of intended

Mistakenly have used the incorrect symbol

↑ mistaken as the letter T, leading to misinterpretation as the start of a drug name, or mistaken as the numbers 4 or 7 

Use increase and decrease

/ (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



Mistaken as the number 2 

Use at



Mistaken as the number 2 

Use and


Plus or and

Mistaken as the number 4 

Use plus, and, or in addition to



Mistaken as a zero (e.g., q2° seen as q20)

Use hr, h, or hour

Ф or ᴓ†

Zero, null sign

Mistaken as the numbers 4, 6, 8, and 9 

Use 0 or zero, or describe intent using whole words



Mistaken as a number sign

Use the metric system (kg or g) rather than pounds

Use lb if referring to pounds 

Apothecary or Household Abbreviations

Explicit apothecary or household measurements may ONLY be safely used to express the directions for mixing dry ingredients to prepare topical products (e.g., dissolve 2 capfuls of granules per gallon of warm water to prepare a magnesium sulfate soaking aid). Otherwise, metric system measurements should be used.



Mistaken as gram

Use the metric system (e.g., mcg, g)



Mistaken as doctor

Use the metric system (e.g., mL)



Mistaken as minutes

Use the metric system (e.g., mL)



Mistaken as zero or 02

Use the metric system (e.g., mL)



Mistaken as tablespoon(s)

Use the metric system (e.g., mL)

tbsp or Tbsp


Mistaken as teaspoon(s)

Use the metric system (e.g., mL)

Common Abbreviations with Contradictory 

Contradictory Meanings


For additional information and tables from Neil Davis ( containing additional examples of abbreviations with contradictory or ambiguous meanings, please click here.


Breast, brain, or bladder

Use breast, brain, or bladder


Cerebral, coronary, or carotid 

Use cerebral, coronary, or carotid

D or d

Day or dose 
(e.g., parameter-based dosing formulas using D or d [mg/kg/d] could be interpreted as either day or dose [mg/kg/day or mg/kg/dose]; or x3d could be interpreted as either 3 days or 3 doses)

Use day or dose


Hand or hip

Use hand or hip


Impaired or improvement

Use impaired or improvement


Liver or lung

Use liver or lung


No or normal

Use no or normal


Pancreas, prostate, preeclampsia, or psychosis

Use pancreas, prostate, preeclampsia, or psychosis


Special or standard

Use special or standard

SS or ss

Single strength, sliding scale (insulin), signs and symptoms, or ½ (apothecary)

SS has also been mistaken as the number 55 

Use single strength, sliding scale, signs and symptoms, or one-half or ½

** On The Joint Commission’s “Do Not Use” list
†   Relevant mostly in handwritten medication information

While the abbreviations, symbols, and dose designations in the Table should NEVER be used, not allowing the use of ANY abbreviations is exceedingly unlikely. Therefore, the person who uses an organization-approved abbreviation must take responsibility for making sure that it is properly interpreted. If an uncommon or ambiguous abbreviation is used, and it should be defined by the writer or sender. Where uncertainty exists, clarification with the person who used the abbreviation is required.

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