MSA! Articles

ISMP Updates Its List of Drug Name Pairs with Tall Man Letters

ISMP extends its sincere thanks to all who completed our survey1 on the use of tall man lettering to differentiate products with look-alike names. “Tall man” lettering, a term coined by ISMP, describes a method for differentiating the unique letter characters of similar drug names known to have been confused with one another. Highlighting a unique portion of a drug name with upper case letters or by other means such as color, contrasting background, bolding, italicizing, or combinations of several factors, can draw attention to the dissimilarities between look-alike drug names. Several studies have shown that the utilization of tall man lettering to differentiate products with look-alike names makes it easier to distinguish drug names and results in fewer errors.2-4 From the 424 survey responses we received, the vast majority of respondents agreed with what the studies are showing. About 81% of respondents felt that the use of tall man letters by the medical product industry helps to reduce drug selection errors, while 14% of the respondents were unsure. More compelling is the fact that 64% of respondents reported that tall man lettering had actually prevented them from dispensing or administering the wrong medication in their practice.

Scope and effectiveness of tall man letters. Approximately half of all respondents reported that their facility uses tall man lettering for similar drug names that appear on pharmacy computer drug selection screens, computer-generated pharmacy labels, shelf labels, automated dispensing cabinet screens, and computer-generated medication administration records (MARs). Between 42-44% of respondents also use tall man lettering at their facility for similar drug names that appear on computerized prescriber order entry (CPOE) screens, smart pump libraries, and preprinted/ standard order sets (see Table 1). Two-thirds to three-quarters of respondents who use tall man letters with look-alike drug name pairs felt this strategy was effective in reducing the risk of errors. Use on computer-generated pharmacy labels and pharmacy drug selection screens was the most prevalent and considered to be the most effective; use on preprinted orders and in smart pump libraries was among the least prevalent and considered the least effective. While some respondents were undecided about the effectiveness of tall man letters, very few felt tall man letters were wholly ineffective in reducing errors (see Table 1).

Use and Effectiveness of Tall Man Letters
Table 1. Use and Perceived Effectiveness of Tall Man Letters

Selection of name pairs for tall man letters. For respondents who use tall man letters, 35% told us they use this strategy for 1-16 drug name pairs; 28% use it for 17-25 pairs; 13% for 26-36 pairs; and 24% for more than 36 name pairs. Resources used to select the drug name pairs targeted for tall man letters included the ISMP list of name pairs with recommended tall man letters (63%), the FDA-approved list of name pairs with tall man letters (53%), and internal risk and error data (37%). Drug information vendors (e.g., Medi-Span, First DataBank, Lexi-Comp) were cited as additional resources.

Communication of name pairs with tall man letters. The purpose and intended use of name pairs that require tall man letters are communicated to staff primarily via inservices, educational programs, and orientation (47%). Other respondents told us they also utilize staff meetings (42%), posters or memos posted on units (39%), and the dissemination of a tall man lettering policy (42%) to communicate this information to staff. Posting on an Intranet site and providing annual updates were also listed as ways to educate staff about tall man letters. Some respondents reported that the purpose and use of tall man letters has not been communicated to staff; instead, their use has been integrated into the system without explanation. We encourage communicating to staff the use and value of tall man lettering during orientation and annual staff competency programs.

Methods of expressing letter characters. When respondents were asked to rank various methods of distinguishing unique letter characters in look-alike name pairs, the use of uppercase letters (i.e., tall man letters) was, by far, the most prevalent choice. Other methods were ranked in the following order: bold font, color font, color back-ground, and the use of a different font. Almost half of the respondents believed that the combination of uppercase letters and the use of bold type or color/color background would be optimal. Very few respondents thought that underlining and reverse print (e.g., dark background with white lettering) would help differentiate the unique letter characters in the look-alike name pairs. 

Update of ISMP’s list. One of the primary reasons for conducting this survey was to utilize the findings to update ISMP’s current list of look-alike drug name pairs with tall man letters. In the survey, we listed eight potential new name pairs that warranted consideration. Of these, approximately three-quarters of respondents agreed that the tall man letters suggested in the survey would help prevent mix-ups between: SUMAtriptan and ZOLMitriptan; valACYclovir and valGANCiclovir; ARIPiprazole and RABEprazole; ISOtretinoin and tretinoin; and fluvoxaMINE and flavoxATE. About two-thirds of respondents agreed that the tall man letters suggested in the survey may help prevent mix-ups between: risperiDONE, rOPINIRole, and risperDAL; and CARac and KURic. Only half of the respondents thought mix-ups would be prevented by using the tall man letters suggested with PRALAtrexATE and PEMEtrexED. A number of respondents suggested that using tall man letters in two different sections of the drug name was confusing and difficult to read; a few even suggested that using tall man letters in the two sections of each drug name made them look more similar than different, and we agree.

Many respondents shared their thoughts regarding other drug name pairs that were not included in the survey. We reviewed each suggestion carefully, placing emphasis on the potential for patient harm, the frequency of use for each medication, and the need to keep the list short enough to avoid diluting the effectiveness of tall man letters. Table 2 provides an updated list of drug name pairs with suggested tall man letters. Based on this survey, we added seven of the eight surveyed name pairs, along with two oncology drug name pairs recommended by ISMP Canada,5 and seven new names or name pairs submitted by respondents. The new name pairs (or individual drug names) added to the list are highlighted in red in Table 2. The current FDA list of generic drug names with required tall man letters is also included.

drug name pairs with tall man letters
Table 2. Drug Name Pairs with Tall Man Letters (new names in red)

**This list is not an official list approved by FDA. It is intended for voluntary use by healthcare practitioners, pharmaceutical companies, and drug information vendors. Changes in official product labeling require FDA approval.

Standardization of tall man letters. Difficulties with the use of tall man letters include inconsistent application in health settings and lack of standardization regarding which name pairs to include as well as which letters to present in uppercase. A new study by Gerrett6 describes several ways to determine which of the dissimilar letters in each drug name should be highlighted. To promote standardization, ISMP followed one of these tested methodologies whenever possible. Called the CD3 rule, the methodology suggests working from the left of the word first by capitalizing all the characters to the right once two or more dissimilar letters are encountered, and then, working from the right of the word back, returning two or more letters common to both words to lowercase letters. When the absolute application of the rule cannot be applied because there are no common letters on the right side of the word, the methodology suggests an approach that results in capitalizing the central part of the word only. ISMP suggests that the tall man lettering scheme provided by FDA and ISMP for the drug name pairs listed in Table 2 be followed to promote consistency.

Again, we thank all who responded to our survey! Your responses and suggestions clearly helped update the list of drug name pairs and recommended tall man letters.


  1. ISMP. Survey on tall man lettering to reduce drug name confusion. ISMP Medication Safety Alert! July 1, 2010;4. 
  2. Filik R, Purdy K, Gale A, Gerrett D. Drug name confusion: evaluating the effectiveness of capital (“Tall Man”) letters using eye movement data. Social Science & Medicine. 2004;59(12):2597-2601.
  3. Filik R, Purdy K, Gale A, Gerrett D. Labeling of medicines and patient safety: evaluating methods of reducing drug name confusion. Human Factors. 2006;48(1):39-47.
  4. Grasha A. Cognitive systems perspective on human performance in the pharmacy: implications for accuracy, effectiveness, and job satisfaction. Alexandria (VA): NACDS; 2000 Report No. 062100.
  5. ISMP Canada. Application of TALLman lettering for drugs used in oncology. ISMP Canada Safety Bulletin. November 11, 2010;1-4.
  6. Gerrett D, Gale AG, Darker IT, Filik R, Purdy KJ. Tall man lettering. Final report of the use of tall man lettering to minimise selection errors of medicine names in computer prescribing and dispensing systems. Loughborough University Enterprises Ltd.; 2009

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