The Legacy of Latin in Your Prescription
For centuries, Latin was the universal language of medicine and science. This tradition continues today in the form of the abbreviated language, or 'Sig codes,' written on prescriptions [1.4.2]. These codes provide pharmacists with instructions for the patient on how to take their medication. One such abbreviation is 'as,' which stands for auris sinistra, the Latin term for 'left ear' [1.2.2, 1.2.3]. It directs the pharmacist to label a medication, most commonly ear drops, for administration in the left ear.
This is part of a trio of Latin-derived abbreviations related to the ears [1.3.1, 1.3.3]:
- AS (auris sinistra): left ear
- AD (auris dextra): right ear
- AU (auris utraque): each ear or both ears
For example, a prescription might read: "Otic solution, 2 gtt as bid." This instructs the patient to instill two drops in their left ear twice a day [1.4.1]. While these abbreviations have a long history, their use is now discouraged by many healthcare organizations to improve clarity and patient safety.
The Dangers of Ambiguity: Why 'AS' is Error-Prone
Medication errors are a significant concern in healthcare. A study analyzing data from 682 facilities found that 4.7% of medication errors were attributed to the use of abbreviations [1.6.1, 1.6.4]. The primary issue with abbreviations like 'as', 'ad', and 'au' is their potential for being misinterpreted.
The Institute for Safe Medication Practices (ISMP) includes these on its list of error-prone abbreviations that should be avoided [1.5.1, 1.5.3]. The main risk is confusion with similar abbreviations for the eyes [1.3.7]:
- OS (oculus sinister): left eye
- OD (oculus dexter): right eye
- OU (oculus uterque): both eyes
A poorly handwritten 'a' can easily look like an 'o', leading a pharmacist or nurse to dispense or administer eardrops into a patient's eye, which could cause significant harm [1.3.5, 1.3.7]. Because of this risk, the recommended best practice is to spell out the full words: "left ear," "right ear," or "both ears" [1.3.2].
Comparison of Auricular and Ocular Abbreviations
To prevent medication errors, it is crucial for both healthcare professionals and patients to understand the distinction between these similar-looking abbreviations. Using the full terms eliminates any ambiguity.
| Abbreviation | Latin Origin | Meaning | Potential for Error | Best Practice |
|---|---|---|---|---|
| AS | auris sinistra | Left Ear [1.2.2] | Easily confused with OS (left eye) [1.3.6] | Write "Left Ear" [1.3.2] |
| AD | auris dextra | Right Ear [1.3.1] | Easily confused with OD (right eye) [1.3.6] | Write "Right Ear" [1.3.2] |
| AU | auris utraque | Both Ears [1.3.2] | Easily confused with OU (both eyes) [1.3.7] | Write "Each Ear" [1.3.2] |
| OS | oculus sinister | Left Eye [1.3.1] | Can be confused with AS (left ear) | Write "Left Eye" [1.3.2] |
| OD | oculus dexter | Right Eye [1.3.1] | Can be confused with AD (right ear) | Write "Right Eye" [1.3.2] |
| OU | oculus uterque | Both Eyes [1.3.2] | Can be confused with AU (both ears) | Write "Each Eye" [1.3.2] |
The Shift to E-Prescribing and Clearer Communication
The push to reduce medication errors has been a major driver for the adoption of electronic prescribing (e-prescribing). E-prescribing systems can significantly reduce errors by eliminating illegible handwriting, which is responsible for millions of clarification calls from pharmacists to providers annually in the U.S. [1.7.1]. One study showed that implementing e-prescribing reduced errors from 42.5 to just 6.6 per 100 prescriptions [1.7.1]. These systems often use standardized, pre-populated drop-down menus for directions, which helps avoid the use of dangerous abbreviations [1.7.5]. For example, a study found e-prescribing led to a 94% reduction in errors caused by inappropriate abbreviations [1.7.1].
Even with these technological advancements, patient vigilance remains key. Always review your medications with your pharmacist. If you see an abbreviation you don't understand on your prescription instructions, ask for clarification to ensure you are taking your medication safely and effectively.
Conclusion
In pharmacology, the abbreviation 'as' means auris sinistra, or 'left ear' [1.2.2, 1.2.3]. While it has historical roots in the language of medicine, it is now on the ISMP's list of error-prone abbreviations because it can be easily confused with 'os' for 'left eye' [1.5.1, 1.3.2]. To safeguard against medication errors, the current best practice is to avoid such abbreviations and write out the full instructions, a transition supported by the increasing use of e-prescribing technologies [1.3.2, 1.7.1]. Patients should always seek clarity from their pharmacist or healthcare provider if they are unsure about any part of their prescription.
For more information on safe medication practices, consult resources from the Institute for Safe Medication Practices (ISMP). https://www.ismp.org/
