Prescription Terminologies

A prescription has a standard structure and uses a set of traditional (mostly Latin-derived) abbreviations. Here's a breakdown, based on Katzung's Basic and Clinical Pharmacology chapter on Rational Prescribing & Prescription Writing plus standard pharmacology reference.

1. Parts of a Prescription

Part	Description
Superscription	Date, patient's name, age, address, weight (for pediatric/weight-based dosing)
Rx symbol	"Recipe" - Latin for "take thou" - the traditional heading of a prescription
Inscription	Name and strength/dose of the drug prescribed
Subscription	Dispensing instructions to the pharmacist (e.g., quantity to dispense, form)
Signatura (Sig)	Instructions to the patient on how to take the medication - what actually appears on the medicine label
Prescriber's signature/DEA number	Legal validation, required for controlled substances

2. Common Latin Abbreviations Used in the "Sig" (Directions)

Frequency/Timing

qd - every day (largely discouraged now due to error potential; write "daily")
bid - twice a day (bis in die)
tid - three times a day (ter in die)
qid - four times a day (quater in die)
q4h, q6h, q8h - every 4/6/8 hours
qhs - every night at bedtime (quaque hora somni)
qam / qpm - every morning / every evening
prn - as needed (pro re nata)
stat - immediately (statim)
ac - before meals (ante cibum)
pc - after meals (post cibum)

Route of Administration

po - by mouth (per os)
pr - per rectum
pv - per vagina
IM - intramuscular
IV - intravenous
SC/SQ - subcutaneous
SL - sublingual
top - topically
inh - by inhalation
gtt - drops (guttae)

Quantity/Dose

tab - tablet
cap - capsule
ml/cc - milliliter/cubic centimeter
gm/mg/mcg - gram/milligram/microgram
ss - one-half (semis)
ut dict / UD - as directed (ut dictum)

Dispensing Instructions

disp - dispense
# - number (quantity to dispense)
NR - no refill
Rep / refill x__ - number of refills
NS - normal saline
D5W - dextrose 5% in water

3. Important Safety Note (from Katzung, highlighted as a common source of prescribing error)

Certain abbreviations are now flagged as error-prone by patient safety organizations (e.g., ISMP, Joint Commission) and should be avoided in favor of writing the term out in full:

qd (once daily) - easily misread as qid (four times daily) → write "daily"
U (units) - misread as "0" (zero), causing 10-fold overdose → write "units"
μg (microgram) - misread as "mg" → write "mcg"
Trailing zeros (e.g., 1.0 mg) - misread as 10 mg → write "1 mg"
No leading zero (e.g., .5 mg) - misread as 5 mg → write "0.5 mg"

Katzung's chapter explicitly notes: "Poor prescription writing is traditionally exemplified by illegible handwriting. However, other types of poor writing are common and often more dangerous. One of the most important is the misplaced or omitted decimal point..." - Katzung's Basic and Clinical Pharmacology, 16th Ed., Ch. 66.

4. Other Key Terms

Generic name vs. Brand (trade) name - the drug's official nonproprietary name vs. its manufacturer's marketed name
DAW - dispense as written (no generic substitution)
NDC - National Drug Code, unique product identifier
e-prescribing (e-Rx) - electronic transmission of prescriptions, now standard/mandated in many jurisdictions and reduces handwriting-related errors

If you want, I can go deeper into a specific area, such as controlled-substance prescription requirements (DEA schedules, triplicate forms) or pediatric weight-based prescription writing.

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