How do you spot the main types of prescription errors?
PTCB topic: Types of prescription errors
- Five error types: wrong drug, patient, dose, quantity and route.
- Name the error by asking what differs from the prescription.
- Quantity = units per dose × doses per day × days.
- Convert before comparing strengths: 0.125 mg = 125 mcg.
- Ear drops labeled for the eye are a wrong-route error.
Key facts
- Wrong drug: a different drug is dispensed, even if the strength and directions match the prescription.
- Wrong patient: a correctly filled prescription or dose goes to someone it was not meant for.
- Wrong dose includes the wrong strength, the wrong volume of a liquid and the wrong frequency, such as daily instead of weekly.
Show all 7 key factsShow fewer
- Quantity check: units per dose x doses per day x days = quantity to dispense.
- Liquid dose check: ordered mg x (mL / mg in the concentration) = mL per dose.
- Convert before comparing strengths: 1 mg = 1,000 mcg, so 0.125 mg = 125 mcg.
- Wrong route: the right drug labeled for the wrong way or site, such as ear drops labeled for the eye or a sublingual tablet labeled to swallow.
Quick check1 question · 2 more at the end
Two patients, Maria Lopez and Mario Lopez, have prescriptions ready at the same time. Maria's correctly filled and labeled prescription is handed to Mario. Which type of prescription error is this?
Correct answer: A.
A wrong-patient error happens when a correctly filled prescription, or a dose, goes to someone it was not meant for. Similar names make this more likely, which is why pharmacies confirm a second identifier, such as date of birth, at pickup. NCC MERP lists wrong patient as its own error type.
A Correct: the right product went to the wrong person, which is a wrong-patient error.
B The drug in the bag matches Maria's prescription; the problem is who received it.
C The dose on the label is correct for Maria; it went to the wrong person.
D The count matches the prescription; the problem is who received it.
Full lesson
Each part starts with its main idea. Open a part when you want the details.
The short answer: Name the error by what went wrong: a different drug is a wrong-drug error, the right drug for someone else is wrong patient, the wrong amount per dose is wrong dose, the wrong count is wrong quantity, and the wrong way of giving it is wrong route. Catch dose and quantity errors by recalculating from the prescription.
1 What are the main types of prescription errors?The 2026 PTCE outline names five prescription error types, and each one describes what differs from the prescription. 1 min
The 2026 PTCE outline names five prescription error types, and each one describes what differs from the prescription. They are wrong dose, quantity, patient, drug and route. NCC MERP's error taxonomy splits some of these further (it lists wrong strength by name) and adds others, such as wrong dosage form and wrong time.
| Error type | What went wrong | Example |
|---|---|---|
| Wrong drug | A different drug was dispensed | hydrOXYzine filled with hydrALAZINE |
| Wrong patient | The right prescription went to the wrong person | Maria's bag handed to Mario |
| Wrong dose | Wrong strength, volume or frequency | 250 mcg tablets for a 0.125 mg order |
| Wrong quantity | The count or volume does not cover the days ordered | 20 capsules for a 30-capsule course |
| Wrong route | Right drug, wrong way or site | Ear drops labeled "in the eye" |
To name the error, ask one question: what is different from the prescription? If only the person is different, it is wrong patient. If the product is different, it is wrong drug, even when the strength and directions match.
2 How do you catch a wrong quantity?You catch a wrong quantity by recalculating the quantity from the directions before you trust the count. 1 min
You catch a wrong quantity by recalculating the quantity from the directions before you trust the count.
Quantity = units per dose x doses per day x days
- Amoxicillin 500 mg, 1 capsule three times daily for 10 days: 1 x 3 x 10 = 30 capsules. Twenty capsules would run out on day 7.
- 1 tablet twice daily for a 30-day supply: 1 x 2 x 30 = 60 tablets, not 30.
- Liquids work the same way: 5 mL three times daily for 10 days = 150 mL.
For a taper, add each step separately. For example, 4, 3, 2 and then 1 tablet daily, each for 3 days, totals 30 tablets.
3 How do you catch a wrong dose?You catch a wrong dose by putting the label's amount back into the prescription's units and comparing. 1 min
You catch a wrong dose by putting the label's amount back into the prescription's units and comparing.
- Liquids: mL per dose = ordered mg x (mL / mg). For amoxicillin 400 mg/5 mL with 400 mg ordered, the dose is 5 mL. A label saying 10 mL gives 800 mg, a twofold overdose.
- Strength: convert first. 1 mg = 1,000 mcg, so a digoxin 0.125 mg order is 125 mcg. Filling with 250 mcg tablets doubles the dose.
- Frequency: alendronate 70 mg is taken once weekly. A label that says daily gives 7 x 70 = 490 mg a week.
Error-prone abbreviations feed dose errors too. A "U" for units can be misread as a zero, turning 10 units into 100.
4 How do you catch a wrong route?You catch a wrong route by matching the dosage form to the words on the label. 1 min
You catch a wrong route by matching the dosage form to the words on the label.
- Otic means ear. The otic suspension label reads "for use in ears," so "instill in the eye" is a route error.
- Sublingual means under the tongue. Nitrostat is dissolved under the tongue or in the buccal pouch without swallowing, so "swallow 1 tablet" is wrong.
- Ophthalmic means eye, and oral means by mouth.
5 What the technician doesThe technician recalculates, compares and flags, and the pharmacist makes the final call. 1 min
The technician recalculates, compares and flags, and the pharmacist makes the final call. Check the stock bottle's drug and strength against the prescription, recount the quantity, and redo the dose math on every liquid. Bring anything unusual to the pharmacist, such as a dose that seems far too large.
Common mistakes
The traps students fall into most. Read these before you practice.
Watch out: A perfect label with the wrong count is a quantity error, not a dose error.
Watch out: Ten mL of a 400 mg/5 mL suspension is 800 mg, not 400 mg.
Watch out: 0.25 mg is 250 mcg, not 25 mcg.
Watch out: Weekly changed to daily is a sevenfold dose error, not a minor label slip.
How to remember it
Five quick questions cover all five error types on every prescription you check.
Memory hook: "Who, What, How much, How many, How." Who = patient, What = drug and How much = dose. How many = quantity, and How = route.
Self-check:
- A correct prescription goes to a patient with a similar name. Which error type is it?
- How many capsules does "1 capsule three times daily for 10 days" need?
- How many mg are in 10 mL of a 400 mg/5 mL suspension?
Show answers
- Wrong patient.
- The prescription itself is correct.
- Only the person is different, so it is a wrong-patient error.
- 30 capsules.
- Quantity = units per dose × doses per day × days.
- 1 × 3 × 10 = 30 capsules.
- 800 mg.
- The suspension has 400 mg in every 5 mL.
- 10 mL is 2 × 5 mL.
- 2 × 400 mg = 800 mg.