By the end of this chapter, you should be able to:
4.Interpret and translate standard prescription sig codes, including route, frequency, and timing abbreviations.
5.Convert between metric, apothecary, and household units of measure with accuracy.
6.Identify the key elements of a valid prescription and the legal requirements for controlled substance prescriptions under the DEA Controlled Substances Act and 21 CFR.
7.Distinguish between the five DEA schedules based on accepted medical use and abuse potential.
8.Recognize common high-alert medications and the safety standards recommended by the ISMP.
9.Apply the core principles of the HIPAA Privacy Rule to patient information handling.
10.Perform accurate days-supply and quantity calculations for common dosage forms.
1.1 The Prescription: Anatomy and Legal Requirements
A prescription is a legal order for a medication. Every prescription, whether written, electronic, or verbal, must contain specific elements to be valid. Missing elements are a common reason for a pharmacist to contact the prescriber.
Core elements of a prescription:
Patient's full name and address
Date of issue
Drug name (and strength, if applicable)
Dosage form (e.g., tablet, capsule, solution)
Quantity to be dispensed (in both numeric and written form for controlled substances)
Directions for use (the "Sig")
Prescriber's name, address, DEA number (for controlled substances), and signature
Types of prescriptions:
Written: Handwritten or printed on tamper-resistant paper.
Electronic (e-prescribing): Transmitted directly from the prescriber's system to the pharmacy. This is the most common and reduces errors from illegible handwriting.
Verbal (telephone): Taken by a pharmacist or, in some states, a trained technician. Verbal orders for controlled substances (Schedule II) are generally prohibited except in specific emergency situations, and must be followed by a written prescription within a set timeframe.
Refill indicators: The prescriber must indicate the number of refills. For Schedule II drugs, refills are never permitted; a new prescription is required each time. Schedule III–V drugs may be refilled up to five times within six months of the original date of issue.
1.2 Sig Codes: The Universal Language of Directions
Sig codes are abbreviations derived from Latin. They tell the patient what to take, how to take it, and when. Accuracy is critical—a single letter can change the dose by a factor of four.
Common Routes of Administration:
PO: by mouth (per os)
PR: by rectum
SL: sublingual (under the tongue)
BU: buccal (between cheek and gum)
TOP: topical (on the skin)
OPH: ophthalmic (in the eye)
OTIC: in the ear
INH: inhaled
IV, IM, SC: intravenous, intramuscular, subcutaneous (injections)
ID: intradermal
Common Frequencies:
QD or q.d.: once daily (this is on the ISMP list of error-prone abbreviations; write "daily")
BID or b.i.d.: twice daily
TID or t.i.d.: three times daily
QID or q.i.d.: four times daily
QHS: at bedtime (hora somni)
QAM: in the morning
QPM: in the evening
PRN: as needed (pro re nata)
AC: before meals (ante cibum)
PC: after meals (post cibum)
Q4H, Q6H, Q8H: every 4, 6, or 8 hours
STAT: immediately
BID AC: twice daily before meals
Common Measurement and Quantity Terms:
Tab: tablet
Cap: capsule
Gtt(s): drop(s)
Susp: suspension
Sol: solution
Ung / Oint: ointment
Cr: cream
Supp: suppository
Amp: ampule
MDI: metered-dose inhaler
AA: of each
Ad: up to
C: with (cum)
S: without (sine)
Sig: write on label (signa)
Disp: dispense
NR: no refill
UTD: as directed (ut dictum)
Critical Trap: The abbreviation "q.d." is frequently misread as "q.i.d." (once daily vs. four times daily). This is a leading cause of medication errors. Similarly, "U" for units is often mistaken for a zero, leading to a 10-fold overdose; always write "units." The PTCB expects you to know the correct meaning of the abbreviation, but also to recognize that these are unsafe abbreviations in practice.
1.3 Systems of Measurement and Conversions
You must be fluent in three systems: metric, apothecary, and household. The metric system is the standard for pharmacy, but you will encounter the others on prescriptions.
Metric System (Base Units):
Mass: gram (g), milligram (mg), microgram (mcg)
Volume: liter (L), milliliter (mL)
Length: meter (m), centimeter (cm)
Key Metric Conversions (Memorize):
1 g = 1000 mg
1 mg = 1000 mcg
1 L = 1000 mL
1 mL = 1 cc (cubic centimeter)
Household System (Used for Patient Convenience):
1 teaspoon (tsp) = 5 mL
1 tablespoon (tbsp) = 15 mL
1 fluid ounce (fl oz) = 30 mL
1 cup = 8 fl oz = 240 mL
1 pint = 16 fl oz = 480 mL (approx. 500 mL)
1 quart = 32 fl oz = 960 mL (approx. 1 L)
1 gallon = 128 fl oz = 3840 mL
Apothecary System (Rare but Tested):
1 grain (gr) = 60 mg (or 65 mg, but 60 is used for calculations)
1 ounce (oz) = 30 g (apothecary ounce for weight)
1 fluid dram = 5 mL (approx. 1 tsp)
1 minim = 0.06 mL (approx. 1 drop)
Weight Conversions for Patients:
1 kg = 2.2 lb
To convert pounds to kilograms: divide pounds by 2.2.
Temperature:
°F = (°C × 9/5) + 32
°C = (°F − 32) × 5/9
Common Calculation Errors: The most frequent error is moving the decimal incorrectly. For example, converting 500 mg to grams: 500 mg ÷ 1000 = 0.5 g, not 5 g. Another common error is confusing 1 tsp (5 mL) with 1 tbsp (15 mL)—a threefold difference.
1.4 Days Supply and Quantity Calculations
You will be asked to determine how many tablets to dispense or how many days a supply will last.
Formula:
Quantity needed = (Dose per administration × Frequency per day) × Days of therapy
Days supply = Total quantity dispensed ÷ (Dose per administration × Frequency per day)
Example 1 (Tablets):
Rx: Drug X 500 mg, take 1 tablet PO BID for 10 days.
Daily dose = 1 tab × 2 = 2 tabs/day
Total quantity = 2 tabs/day × 10 days = 20 tablets
Example 2 (Liquids):
Rx: Drug Y 250 mg/5 mL, take 500 mg PO QID for 7 days.
Dose per administration = 500 mg ÷ 250 mg per 5 mL = 2 × 5 mL = 10 mL
Daily volume = 10 mL × 4 (QID) = 40 mL/day
Total volume = 40 mL/day × 7 days = 280 mL
Example 3 (Days Supply):
Rx: Drug Z, take 1 tablet PO QID. Dispense 120 tablets.
Daily use = 4 tablets/day
Days supply = 120 ÷ 4 = 30 days
Insulin and Drops: For insulin, calculate based on total daily units. For eye/ear drops, estimate based on drops per mL (typically 20 drops/mL for ophthalmic solutions). If a patient uses 2 drops in each eye BID, that is 8 drops/day. A 15 mL bottle = 300 drops (15 × 20), so the supply is 300 ÷ 8 = 37.5 days.
1.5 DEA Controlled Substances Act and Schedules
The DEA Controlled Substances Act and 21 CFR govern the prescribing and dispensing of controlled substances. The law classifies drugs into five schedules based on two factors: accepted medical use and abuse potential.
Schedule I (C-I): High abuse potential, no accepted medical use in the US. Examples: heroin, LSD, marijuana (federally), ecstasy. Cannot be prescribed.
Schedule II (C-II): High abuse potential with severe psychological or physical dependence liability, but accepted medical use. Examples: oxycodone, morphine, fentanyl, amphetamine (Adderall), methylphenidate (Ritalin), hydrocodone (alone). No refills. Written prescription required (no verbal except emergency).
Schedule III (C-III): Moderate to low abuse potential. Examples: Tylenol with codeine (acetaminophen/codeine), ketamine, anabolic steroids. Up to 5 refills in 6 months.
Schedule IV (C-IV): Low abuse potential. Examples: alprazolam (Xanax), diazepam (Valium), lorazepam (Ativan), zolpidem (Ambien), tramadol. Up to 5 refills in 6 months.
Schedule V (C-V): Lowest abuse potential. Examples: cough syrups with codeine (e.g., promethazine with codeine), loperamide (in some formulations), pregabalin (Lyrica is C-V). Up to 5 refills in 6 months. Some states allow "pharmacy legend" sales without a prescription for C-V products, with limits on quantity and patient identification.
DEA Number Verification: A prescriber's DEA number has a specific format: two letters (first is the registrant type, second is the first letter of the last name), followed by seven digits. The check digit is calculated by adding the 1st, 3rd, and 5th digits, then adding the 2nd, 4th, and 6th digits multiplied by 2, and summing those two results. The last digit of the sum must equal the 7th digit.
1.6 High-Alert Medications and ISMP Recommendations
The Institute for Safe Medication Practices (ISMP) maintains a list of high-alert medications—drugs that bear a heightened risk of causing significant patient harm when used in error. You must recognize these and apply extra safeguards.
Methotrexate (especially when prescribed daily instead of weekly)
ISMP Recommendations (Key Points):
Use tall man lettering to differentiate look-alike drug names (e.g., DOBUTamine vs. DOPamine, hydrOXYzine vs. hydrALAZINE).
Avoid error-prone abbreviations (e.g., "U" for units, "QD" for daily, trailing zeros like "5.0 mg").
Use independent double-checks for high-alert drugs.
Store concentrated electrolytes separately from other medications.
Look-Alike/Sound-Alike (LASA) Pairs: Be aware of pairs like Celebrex (celecoxib), Celexa (citalopram), and Cerebyx (fosphenytoin); Tegretol (carbamazepine) and Tequin (gatifloxacin); Zyprexa (olanzapine) and Zyrtec (cetirizine).
1.7 USP Compounding Standards
Compounding is the preparation of a medication tailored to a patient's specific needs. The United States Pharmacopeia (USP) sets the standards.
USP <795>: Non-sterile compounding (e.g., creams, ointments, capsules, oral solutions). Requires a clean environment, proper gowning, and documentation of ingredients and procedures.
USP <797>: Sterile compounding (e.g., IV admixtures, eye drops). Requires an ISO Class 5 environment (laminar airflow workbench), garbing (gloves, gowns, masks), and strict aseptic technique. Beyond-use dates (BUDs) are assigned based on the risk level (low, medium, high).
USP <800>: Handling of hazardous drugs (e.g., chemotherapy). Requires separate negative-pressure rooms and closed-system transfer devices.
The PTCB will test your understanding of the risk levels and the importance of aseptic technique, not the detailed engineering controls.
1.8 FDA Labeling and REMS
The FDA regulates drug labeling and marketing. The package insert (prescribing information) is the official label for a prescription drug. It contains indications, dosing, contraindications, warnings, and adverse reactions.
REM (Risk Evaluation and Mitigation Strategy): Some drugs have a REMS, a required safety program to ensure the benefits outweigh the risks. Examples include:
Clozapine (Clozaril): Requires monitoring of white blood cell counts (risk of agranulocytosis).
Isotretinoin (Accutane): Requires the iPLEDGE program to prevent pregnancy (teratogenic).
Thalidomide: Requires the STEPS program.
Alosetron (Lotronex): For severe IBS, with a specific prescriber certification.
As a technician, you must verify that the patient is enrolled in the REMS program and that required monitoring has been completed before dispensing.
1.9 HIPAA Privacy Rule
The Health Insurance Portability and Accountability Act (HIPAA) Privacy Rule protects a patient's protected health information (PHI). PHI includes any information that identifies the patient and relates to their health, treatment, or payment.
Key Rules for Technicians:
Do not discuss a patient's medications in public areas (waiting room, hallway).
Do not leave printed labels or patient information unattended.
Only access the minimum necessary information to perform your job.
Do not share passwords or leave computer screens logged on.
When speaking on the phone, verify the identity of the caller before giving any information.
A patient has the right to request a copy of their records and to request corrections.
Violations: Breaches can result in significant civil and criminal penalties. A common trap is thinking that a patient's spouse or adult child can automatically access the patient's records—they cannot unless the patient has given explicit authorization.
1.10 Common Exam Traps
Students often miss questions for predictable reasons. Here are the classic traps and how to avoid them.
189.q.d. vs. q.i.d. (The #1 Trap): A prescription for "1 tab q.d." is once daily. "1 tab q.i.d." is four times daily. The error is a 4-fold overdose. Always read the abbreviation carefully. The PTCB will test this distinction directly.
190.DEA Schedule Confusion: Hydrocodone with acetaminophen (Vicodin) is Schedule II (as of 2014), but many students still think it is Schedule III. Codeine-containing cough syrups (e.g., Tussionex) are Schedule III, but codeine tablets (Tylenol #3) are Schedule III as well. Tramadol is Schedule IV, not a non-controlled drug. Memorize the specific examples, not just the general rules.
191.Metric Decimal Errors: Converting 0.5 g to mg: multiply by 1000 = 500 mg. Converting 500 mcg to mg: divide by 1000 = 0.5 mg. A common error is moving the decimal three places in the wrong direction. Write out the conversion factor every time.
192.Teaspoon vs. Tablespoon: 1 tsp = 5 mL; 1 tbsp = 15 mL. A patient who takes "2 tbsp" instead of "2 tsp" receives 30 mL instead of 10 mL—a 3-fold error. The exam will often ask for the total volume in mL.
193.Days Supply for Insulin: If a patient uses 40 units of insulin daily and the vial is 10 mL of U-100 insulin (100 units/mL), the vial contains 1000 units. Days supply = 1000 ÷ 40 = 25 days. Students often forget to multiply the volume by the concentration.
194.Refills for C-II: There are zero refills for Schedule II drugs. A common trap is a question about a "partial fill" or "refill" of a C-II prescription. The answer is that a new prescription is required.
195."Take as Directed" (UTD): This is a valid sig, but it means the days supply cannot be calculated from the sig alone. If a question asks for days supply and the sig is UTD, you must look for other clues (e.g., quantity, typical dosing) or state that it cannot be determined.
196.High-Alert Drug Mix-Ups: Confusing heparin (anticoagulant) with Hespan (hetastarch, a volume expander), or insulin with Lantus vs. Levemir (both long-acting, but not interchangeable without prescriber approval). The exam will test your recognition of these as high-alert.
197.Compounding BUDs: A low-risk non-sterile compound has a BUD of no more than 14 days when stored at controlled room temperature (unless the USP monograph says otherwise). A sterile low-risk compound prepared in an ISO 5 hood has a BUD of 48 hours at room temperature or 14 days if refrigerated. Students often confuse the two standards.
198.HIPAA "Minimum Necessary": You may only access the information needed to do your job. A technician does not need to know a patient's full medical history to fill a prescription for amoxicillin. The trap is a question where a coworker asks you to look up a friend's profile—this is a violation even if you do not share the information.
Summary
Mastery of this chapter requires memorization of sig codes, conversion factors, and DEA schedules, but it also requires the ability to apply these rules in realistic scenarios. Always double-check your math, read abbreviations in context, and remember that patient safety is the ultimate goal. The regulations you must know—DEA Controlled Substances Act and 21 CFR, FDA labeling and REMS, USP <795>/<797>, ISMP recommendations, and HIPAA—are the framework within which every pharmacy professional operates.
