Medical prescriptions use specialized shorthand to communicate complex instructions quickly and accurately between healthcare providers and pharmacists. This standardized communication ensures the correct medication is dispensed and used appropriately. The key to understanding how a drug is to be taken is found in a specific section of the prescription known as the “Sig,” which provides the instruction set guiding the patient’s treatment regimen.
Defining the “Sig” and Its Purpose
The term “Sig” is an abbreviation for signatura, a Latin word meaning “to write” or “to mark.” This instruction block provides the direct set of directions for the patient on how to use the medication. The prescriber writes the Sig for the pharmacist, who then translates the abbreviated language into clear, full-text instructions on the medication label.
The purpose of the Sig is to ensure patient adherence and safety by providing unambiguous details about the drug’s usage. Without clear instructions, the risk of medication error, such as taking the wrong dose or at the wrong time, increases significantly. The Sig acts as the bridge between the prescriber’s medical decision and the patient’s daily routine.
Essential Components of the Sig
A properly written Sig provides a comprehensive set of instructions by consistently including several specific pieces of information. The first component is the Dose, which indicates precisely how much of the medication is to be taken in a single administration. This detail often specifies the number of tablets, milliliters of liquid, or milligrams of active ingredient.
The second necessary component is the Route of administration, which describes how the medication is to enter the body. This might involve taking it orally, applying it topically, or administering it as an injection. The third element is the Frequency, which dictates how often the drug should be taken over a specific period, such as once daily or three times a day.
Finally, the Sig often includes the Duration or specific conditions for use, telling the patient how long to continue the therapy. For instance, an antibiotic prescription will specify the total number of days to take the medication, while a pain reliever might be prescribed pro re nata, or “as needed”. These elements—Dose, Route, Frequency, and Duration—form the complete guidance for the patient’s treatment.
Common Abbreviations Used in Prescription Instructions
To efficiently communicate these complex instructions, healthcare professionals rely on a standardized set of abbreviations, many of which are derived from Latin terms. The most common abbreviations relate to the frequency and timing of medication administration. For instance, instructions for taking a medication daily use codes like QD (quaque die), meaning “every day,” or BID (bis in die), meaning “twice a day”.
For more frequent dosing, TID (ter in die) indicates “three times a day,” and QID (quater in die) specifies “four times a day”.
Time-specific instructions are also abbreviated, such as AC (ante cibum) for “before meals” and PC (post cibum) for “after meals”. If a medication should be taken at night, the abbreviation HS (hora somni) is used, meaning “at bedtime”.
Abbreviations for the route of administration are equally common and are used to prevent errors in how a drug is delivered. PO (per os) instructs the patient to take the medication “by mouth,” while SL (sublingual) means the drug should be placed “under the tongue”. Other routes include PR (per rectum) for rectal administration and codes for ear or eye drops, such as AD (auris dextra) for the right ear or OS (oculus sinister) for the left eye.