Medical prescriptions are written directions for the preparation and administration of a specific medication or treatment. Prescriptions specify a drug or therapy name, dose, form, delivery route, frequency, timing, and purpose. Additionally, they tell the pharmacist how much to dispense and how many refills are available.
The tables below summarize the most common abbreviations that appear on prescriptions.
- Dangerous abbreviations: Numerous organizations advise medical professionals to minimize or avoid using abbreviations in prescriptions due to the risk that they may be misread or misunderstood. A warning symbol appears next to abbreviations that are particularly prone to causing prescription errors.
- Abbreviation formatting: Abbreviation formatting varies widely by institution (e.g., PRN, prn, p.r.n.). For simplicity, the following tables use lowercase letters for Latin abbreviations and capital letters for English initialisms. Units of measurement are lowercase except when mixed case is recommended to help avoid prescription errors.
For a more comprehensive alphabetical list of abbreviations, consult OpenMD’s index of medical abbreviations.
℞ (or Rx) is an abbreviation for “medical prescription”. It is derived from the Latin word recipe, meaning “take” (recipe is the imperative form of recipere, meaning “to take”). In the 16th century, the word was abbreviated as ℞—the letter R with a line across the leg, which indicated that the R was an abbreviation.
The dose is the amount of a drug to be taken at one time. It is commonly specified in metric mass (e.g., milligrams) or international units (an agreed upon measure of biological effect for a given drug). Prescriptions are occasionally written using apothecary units, such as ounces and teaspoons.
Common abbreviations for medical doses:
|cc||milliliter (cubic centimeter)|
|dg||decigram (0.1 gram)|
|dL||deciliter (0.1 liter)|
|gtt||drop(s) (L. gutta or guttae)|
|mg||milligram (0.001 gram)|
|mL||milliliter (0.001 liter)|
|ss||one half (L. semis)|
|ss||sliding scale (for insulin)|
Dosage form indicates the physical form of the medication, including active and inert ingredients. The form is selected to maximize drug efficacy and safety while simplifying administration. The form may be solid (e.g., tablets and capsules), semi-solid (e.g., ointments and creams), liquid (e.g., syrups and drops), or gas (e.g., inhalers and aerosols).
|pulv||powder (L. pulvis)|
|ung||ointment (L. unguentum)|
The delivery route indicates where the drug is to be administered to the patient. The route may be enteral (ingested or rectal), parenteral (injected), inhaled (through the nose or mouth into the lungs), topical (onto the skin), ophthalmic (into the eye), or otic (into the ear).
|a.u.||each ear, both ears (L. auris utraque)|
|o.d.||right eye (L. oculus dexter)|
|o.s.||left eye (L. oculus sinister)|
|p.o.||by mouth (L. per os)|
|PV, vag||per vagina/vaginally|
From the Latin signatura, meaning “let it be labeled”. This field includes instructions for delivery route and frequency.
Frequency refers to when or how often a medication should be administered. This is typically expressed in terms of how many times per day, week, or month the medication should be taken.
|ad. lib.||as desired, at liberty (L. ad libitum)|
|alt. dieb.||every other day (L. alternis diebus)|
|alt. hor.||alternate hours (L. alternis horis)|
|alt. noct.||alternate nights (L. alternis noctibus)|
|b.i.d.||twice a day (L. bis in die)|
|dieb. alt.||every other day (L. diebus alternis)|
|o.d.||once daily (L. omni die)|
|o.h.||every hour (L. omni hora)|
|o.m.||every morning (L. omni mane)|
|o.n.||every night (L. omni nocte)|
|p.r.n.||as desired/as required (L. pro re nata)|
|q1h||every 1 hour|
|q2h||every 2 hours|
|q3h||every 3 hours|
|q4h||every 4 hours|
|q6h||every 6 hours|
|q.d.||every day, once daily (L. quaque die)|
|q.h.||every hour (L. quaque hora)|
|q.i.d.||four times a day (L. quater in die)|
|q.o.d., q.a.d.||every other day (L. quaque altera die)|
|q.p.||as much as desired (L. quantum placeat)|
|q.s.||a sufficient quantity (L. quantum sufficit)|
|q.v.||as much as desired (L. quantum vis)|
|q.h.s.||at bedtime (L. quaque hora somni)|
|t.i.d.||three times a day (L. ter in die)|
Medications are sometimes labeled PRN, which means “take as needed”. PRN is an abbreviation of the Latin phrase pro re nata, meaning “as the circumstance arises.” Medications with this label include analgesics, laxatives, and some anti-anxiety medications.
Timing and Administration
Instructions for the patient on when or how to take the medication. These instructions are usually intended to maximize the therapeutic effect of a medication or minimize side effects. Directions may include administering the drug at a certain time of day or at a specific time relative to the consumption of food.
|a.a.||of each (L. ana ana)|
|ad||up to (L. ad)|
|aq||water (L. aqua)|
|e.m.p.||as directed (L. ex modo prescripto)|
|ft||make, let it be made (L. fiat)|
|m.p.||as directed (L. modo praescripto)|
|UD, UAD||use as directed|
|ut. dict.||as directed (L. ut dictum)|
|c.c.||with food (L. cum cibos)|
|a.c.||before meals (L. ante cibum)|
|a.m.||morning, before noon (L. ante meridiem)|
|a.p.||before meals (L. ante prandium)|
|h.s.||bedtime (L. hora somni)|
|p.c.||after meals (L. post cibos)|
|p.m.||afternoon/evening (L. post meridiem)|
To reduce the risk of medication errors, prescribers are encouraged to list the intended purpose of the medication (e.g., insomnia, high blood pressure, etc.). This is vital, as it helps pharmacists avoid errors from misreading the medication or dose. It is also important because it helps patients understand the purpose of each medication.
The use of abbreviations in medical prescriptions has led to medical errors and is widely discouraged. When used, care should be taken to ensure that abbreviations are clearly printed and unambiguous in their meaning.
The information included in a prescription ensures that the patient receives the correct medication in the correct amount and that it is administered correctly with the correct frequency. This information is essential for ensuring that the medication is safe and effective for the patient.
- Dangerous Medical Abbreviations by OpenMD
- List of Error-Prone Abbreviations (PDF) by the Institute for Safe Medication Practices
- Medical Abbreviations (A-Z) on OpenMD
- Frances Aguilar, PharmD
- Brian Sullivan, MD
Published: January 20, 2023