Understanding Prescription Abbreviations

Do You Know What the Directions Mean?

Prescription pad
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Centuries ago, all prescriptions were written in Latin. Now, only one section of the prescription (the directions for taking the drug) uses abbreviations derived from Latin. For the average person, who has no medical background, the prescription abbreviations need to be deciphered. Taking the wrong dose of arthritis medication or pain medication can have serious or even fatal consequences. Safe use is tied to your understanding of prescription abbreviations. An example of a serious error associated with a rheumatoid arthritis drug due to improper dosing would be if methotrexate was mistakenly taken daily versus weekly.

You may be thinking that the pharmacy where you fill your prescription does the deciphering for you. While that's true, you should read the prescription and go over the directions with your doctor before you leave his office. 

That said, this is becoming less of an issue since electronic prescriptions are now becoming the norm. If your doctor prescribes electronically, you will never touch the paper prescription, nor see the abbreviations.

The Origins of Using "Rx" for "Prescription"

The origin of "Rx", used as an abbreviation for "prescription", has been attributed to the Latin word "recipe" which means "take". Also, it has been associated with Jupiter, the chief deity of Roman state religion until Christianity became the dominant religion of the Roman Empire. The symbol was placed on prescriptions to invoke the deity's blessing on the medicine to help a person get well. More recently, the cross that sometimes appears at the end of the "R" has been explained as a substitute period.

The Use of Prescription Abbreviations: An Example

An example of what your doctor may write:
Sig: I tab po qid pc & hs

Unless you have a medical background, our example may be unintelligible. In this example, the prescription abbreviations instruct the pharmacist to, "Label the container for this patient's medication with the following instructions: Take one tablet by mouth 4 times a day, after meals and at bedtime."

Common Latin Rx Terms

Some of the common latin prescription abbreviations include:

  • ac (ante cibum) means "before meals"
  • bid (bis in die) means "twice a day"
  • gt (gutta) means "drop"
  • hs (hora somni) means "at bedtime"
  • od (oculus dexter) means "right eye"
  • os (oculus sinister) means "left eye"
  • po (per os) means "by mouth"
  • pc (post cibum) means "after meals"
  • prn (pro re nata) means "as needed"
  • q 3 h (quaque 3 hora) means "every 3 hours"
  • qd (quaque die) means "every day"
  • qid (quater in die) means "4 times a day"
  • Sig (signa) means "write"
  • tid (ter in die) means "3 times a day"

For an In-Depth Listing of Prescription Abbreviations:

Use of Abbreviations Is Slowly in Decline

While the Latin terms are still commonly seen on prescriptions, some doctors are gradually retiring use of these old terms and better clarifying their drug orders in plain language.

Several years ago, since improved readability helps prevent medication mix-ups, it was recommended that prescribers write out instructions rather than use ambiguous abbreviations. For example, prescribers would write "daily" rather than "qd", the abbreviated Latin term for "every day". In this case, "qd" could easily be misinterpreted as "qid" (which means 4 times a day) or "od" (which means right eye).

And as mentioned above, there is e-prescribing (electronic prescribing) which adds another level of improvement to the clarity of prescribing medications.  E-prescribing improves patient safety by eliminating illegible prescriptions, reducing the need for oral communications which can result in miscommunications, warning and alert systems at the point of prescribing, and allowing the prescriber to view a patient's medication history.

The Bottom Line

If you are still issued a written prescription and the directions are unclear or confusing, ask your doctor or pharmacist to explain. Do not take your medication without fully understanding the prescribing instructions. Take no chances.

With e-prescribing, you may not see the directions until they appear on a pill bottle label. At that point, it is your responsibility to ask your pharmacist any questions you have or to verbally review the directions.  Take the necessary time so that you can feel certain about how you are to take the prescribed drug. Do your part to avoid medication errors.

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