Error-Prone Symbols

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The symbols 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 symbols should never be used when communicating medical information.

Symbol Intended 
Misinterpretation Correction
ʒ Dram Mistaken as “3” Use the metric system
Minim Mistaken as “mL” Use the metric system
x3d For three days Mistaken as “3 doses” Use “for three days”
> and < Greater than and less than Mistaken as opposite of intended; incorrect symbol used mistakenly; “<10” mistaken as “40” (forty) Use “greater than” or “less than”
(slash mark)
Separates two doses
or indicates “per”
Mistaken as the number 1 (eg, “25 units/10units” 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 (eg, q2° seen as q 20) Use “hr”, “h”, or “hour”
Φ or ∅ Zero, null sign Mistaken as numerals 4, 6, 8, and 9 Use 0 or zero, or describe intent using whole words

Source: Institute for Safe Medication Practices. Error-Prone Abbreviations, Symbols, and Dose Designations. 2015.

Available at:

(Rev. 7/2016)

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