Types of Prescription Errors
Types of prescription errors, including incorrect dose, quantity, patient, drug, or route of administration.
Types of prescription errors account for 4.0% of the PTCE. This topic tests your ability to categorize what specifically went wrong when a prescription is filled incorrectly — wrong dose, wrong quantity, wrong patient, wrong drug, or wrong route. The organizing framework is the "rights" of medication safety, and most exam questions ask you to identify which "right" was violated in a given scenario.
The Rights of Medication Safety
The classic "five rights" are the right patient, right drug, right dose, right route, and right time (frequency). Expanded versions add the right documentation and right reason. Nearly every prescription error maps to a violated right: dispensing to the wrong patient (right patient), filling amoxicillin when azithromycin was ordered (right drug), 500 mg instead of 50 mg (right dose), or an oral product where an otic/ophthalmic was intended (right route). Framing an error by which right failed is exactly how the exam presents these scenarios.
Almost every prescription error scenario can be sorted into which of the "rights" was violated.
Dose vs. Quantity Errors
A dose error is the wrong strength or amount per administration — for example, dispensing 20 mg tablets when 10 mg was prescribed, or a directions error that has the patient taking twice the intended amount. A quantity error is dispensing the wrong total count or days supply — 30 tablets instead of 90, or a 30-day supply when 90 days was written. These are distinct: the dose can be correct while the quantity is wrong, and vice versa. Wrong quantity also has downstream effects on refill timing and insurance claims.
Dose = strength/amount per administration; quantity = total number dispensed. Do not confuse them.
Where Errors Enter the Process
Prescription errors can originate at prescribing (an illegible or ambiguous order), transcription/data entry (mistyping the drug, sig, or strength), dispensing (pulling the wrong product, miscounting), or administration. Right-patient errors often trace to two patients with the same or similar names, which is why at least two patient identifiers (such as name plus date of birth) are verified. LASA confusion is a frequent source of wrong-drug errors, and misreading the route abbreviation causes wrong-route errors.
Must-Know for the Exam
- ✓The five rights: right patient, right drug, right dose, right route, right time
- ✓Expanded rights add right documentation and right reason
- ✓A dose error is wrong strength/amount; a quantity error is wrong total count or days supply
- ✓Use at least two patient identifiers (e.g., name + date of birth) to prevent wrong-patient errors
- ✓Wrong-drug errors are frequently caused by LASA (look-alike/sound-alike) confusion
- ✓Wrong-route errors often come from misreading route abbreviations
- ✓Errors can enter at prescribing, transcription/data entry, dispensing, or administration
- ✓Most exam scenarios ask which "right" was violated
Common Exam Mistakes
- ✗Confusing a dose error (wrong strength) with a quantity error (wrong total number)
- ✗Verifying only one patient identifier instead of two
- ✗Overlooking route errors from misread abbreviations (e.g., otic vs. ophthalmic)
- ✗Attributing every wrong-drug error to dispensing when it may have started at data entry
- ✗Failing to connect LASA confusion to wrong-drug errors
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Start Types of Prescription Errors Practice Quiz →Key Concepts — Part 1
1. Two patients with the same last name and very similar first names ('Jon Smith' and 'John Smith') are both waiting for prescription pickup. A technician nearly hands the wrong bag to the wrong patient. What type of error does this scenario illustrate?
A wrong-patient error, best prevented by verifying at least two patient identifiers (e.g., name and date of birth)
This scenario is a classic wrong-patient error risk caused by name similarity; verifying two independent identifiers (such as full name plus date of birth) before handoff is the standard prevention strategy. It does not involve route, drug identity, or duplicate therapy issues.
2. A prescription is written for 'Metoprolol succinate ER 50mg,' but due to a similar drug name at data entry, the pharmacy fills it with 'Metoprolol tartrate IR 50mg' instead. What type of error is this?
A wrong-drug error, since the extended-release and immediate-release salts are clinically different products despite the similar name
Even though both are 'metoprolol,' the succinate (extended-release) and tartrate (immediate-release) formulations have different release profiles and dosing schedules, making this a wrong-drug/wrong-formulation error, not an acceptable substitution. Quantity and route are not the issue here -- the wrong product itself was selected.
3. A prescription is written for '10 mg' but a decimal misread during data entry causes the pharmacy system to display '100 mg.' What category of prescription error does this illustrate?
A wrong-dose error caused by a decimal/transcription misread
A misread decimal point that changes the intended strength is a wrong-dose error originating from a transcription mistake -- a tenfold error like this is exactly why leading/trailing zero rules exist. This scenario does not involve the wrong patient, a missing drug, or an incorrect route.
4. A prescriber writes an order for '#30' tablets, but due to a data entry mistake, the pharmacy label and dispensed bottle show '300' tablets. What type of error is this?
A wrong-quantity error caused by an extra digit entered during processing
This is a wrong-quantity error -- the correct drug and dose were selected, but tenfold too many tablets were dispensed due to a data entry mistake. It did reach an actual dispensed product (not just a near miss), and the drug itself and its route were correct.
5. A prescription intended for topical application is entered into the system with oral administration directions by mistake. What type of prescription error is this?
A wrong-route error, since the medication is directed to be used by an incorrect route of administration
When the directions specify an incorrect route of administration for how the drug was intended to be used, this is classified as a wrong-route error -- a potentially serious mistake, since many medications are formulated for only one specific route. Patient identity, quantity, and duplication are not the issue in this scenario.
6. A pharmacy stocks the same antibiotic in both ophthalmic (eye) and otic (ear) drop formulations. A technician selects the otic formulation for a prescription intended for eye use. What type of error does this represent?
A wrong-route error, since using an ear-formulated product in the eye (or vice versa) can cause harm despite being the 'same' drug
Ophthalmic and otic formulations of the same drug are manufactured with different pH, sterility, and additive requirements for their specific site of use; using the wrong one is a wrong-route (site-of-administration) error and can cause irritation or harm, even though both are technically 'drops.' This is a real and clinically significant error type, not just a dosing issue.
7. A prescriber's sig reads 'take one tablet once daily,' but the pharmacy label is entered as 'take one tablet twice daily.' What type of prescription error is this?
A directions/frequency error, resulting in the patient receiving incorrect dosing instructions
Changing the prescribed frequency from once daily to twice daily is a directions error that effectively doubles the patient's intended dose over time -- a meaningful and potentially harmful mistake, not a wrong-patient or wrong-drug issue, and it would reach the patient rather than remain a near miss if not caught.
8. A technician selects a bottle of 20mg tablets from an adjacent bin instead of the prescribed 10mg tablets, due to look-alike packaging. If this reaches the patient, what type of error has occurred?
A wrong-dose (wrong-strength) error caused by an LASA/packaging mix-up
Dispensing the wrong strength of the correct drug is classified as a wrong-dose error; here it was caused by a look-alike packaging mix-up during selection, illustrating how LASA risk factors and error types connect. This is not a route, patient identity, or duplication issue.
9. What is a transcription error, in the context of prescription processing?
A mistake made when manually transferring information from a written or verbal order into the pharmacy's system, such as mishearing a verbal order
A transcription error occurs when information is inaccurately transferred from its original source (handwritten, verbal, or faxed order) into the pharmacy system -- for example, misheard verbal orders or misread handwriting. It can occur with any order type, is a pharmacy-side error, and isn't limited to compounded products.
10. A prescriber sends an e-prescription for two medications, but only one is entered into the patient's profile because the second was overlooked. What type of prescription error is this?
An omission error, since a prescribed medication was left out entirely
An omission error occurs when a prescribed medication (or dose) is left out of processing entirely -- here, the second drug was never entered. This is distinct from a wrong dose or route being given for a drug that was processed, and it's not an intentional substitution.
Key Concepts — Part 2
1. Two patients waiting at pickup have the same last name and similar dates of birth. The technician is about to hand the wrong patient's bag over based on name alone. How should this wrong-patient risk be prevented?
By verifying at least two independent identifiers, such as full name and date of birth, before handoff
Using at least two independent identifiers (e.g., full name plus date of birth) before handoff is the standard practice for preventing wrong-patient errors, especially with similar names. Physical appearance, first name alone, or order-of-arrival are not reliable identity checks.
2. During data entry, a technician selects a similar-looking drug from the pharmacy system's drop-down list because it appeared near the top of the search results, rather than the drug actually prescribed. What type of error is this?
A wrong-drug error caused by selecting the incorrect item during data entry
Selecting an incorrect product from a list -- even due to a system's display order -- results in the wrong drug being entered into the prescription, which is a wrong-drug error. Quantity, omission, and route are not the issue in this specific scenario.
3. A prescription is written for a 10-day course of antibiotics, but the technician enters a 30-day supply into the system, resulting in triple the intended quantity being dispensed. What type of error is this?
A wrong-quantity error caused by an incorrect days-supply entry
Even though the correct drug was selected, entering the wrong days-supply led to an incorrect quantity being dispensed -- this is a wrong-quantity error distinct from a direct quantity typo, since it stems from a days-supply miscalculation.
4. A bar code scan during final dispensing verification alerts the technician that the scanned product does not match the prescription on file. What has this scan most likely helped prevent?
A wrong-drug error from reaching the patient
A bar code mismatch at final verification is specifically designed to catch wrong-drug (or wrong-strength) selection errors before the medication reaches the patient -- this is a safety catch, not related to billing, shipping, or inventory levels.
5. During data entry, a technician mixes up two patient profiles with similar dates of birth, entering a new prescription into the wrong patient's file. What type of error is this, and at what stage did it occur?
A wrong-patient error that occurred at the data entry stage, rather than at pickup/handoff
This is a wrong-patient error, but unlike a mix-up at pickup, it originated earlier -- during data entry, when the prescription was attached to the wrong patient's profile. Understanding where in the workflow an error originates helps target the right corrective action; this scenario does not involve route, dose, or omission issues.
6. A prescription for '10 mg' is written with a trailing zero as '10.0 mg' and misread by a technician as '100 mg' during data entry. If dispensed, what type of error results?
A wrong-dose error stemming from a trailing-zero misread
This scenario shows how a trailing-zero formatting mistake can directly cause a wrong-dose error if a tenfold misread isn't caught -- it connects the error-prevention rule (avoid trailing zeros) to the resulting error type when the rule is violated. Route, patient identity, and omission are not involved here.
7. A technician selects stock based on a partially matching NDC number during a rush, without confirming the full NDC against the prescription. This results in the wrong drug being dispensed. What type of error occurred?
A wrong-drug error caused by relying on an incomplete NDC match
Relying on a partial NDC match instead of confirming the complete, correct code led directly to selecting the wrong product -- a wrong-drug error. Since the incorrect drug was actually dispensed (not just caught in time), this is a completed error, not a near miss, and it isn't a quantity or duplication issue.
8. A prescription is written using the abbreviation 'OU' (meaning both eyes), but due to illegible handwriting, it is misread and processed as 'AD' (right ear) with directions to place drops in only the right ear. What type of error resulted?
A wrong-route error, since the drops were directed to the wrong anatomical site (ear instead of eye) due to abbreviation confusion
Confusing eye-related abbreviations with ear-related directions changes the intended route/site of administration, making this a wrong-route error rooted in an error-prone abbreviation -- a good example of how abbreviation confusion can directly cause a specific prescription error type. It does not involve the drug identity, quantity, or an intentional substitution.
9. A pharmacy fills a prescription for a controlled substance with the correct drug and correct dose, but due to a data-entry mix-up between two similarly named patient profiles, it is dispensed to the wrong patient. Why is this considered a particularly serious type of error?
Because the wrong patient receives a controlled substance they were not prescribed, creating both a safety risk for that patient and potential diversion/accountability concerns for the intended patient's prescription
A wrong-patient error involving a controlled substance is especially serious because the unintended recipient is exposed to a potent medication they weren't evaluated for, and the intended patient's prescription record now reflects a discrepancy relevant to controlled substance accountability. Such errors are absolutely reportable, correct dose/drug does not change the wrong-patient classification, and this alone would not automatically revoke a pharmacy license.
10. Which of the following best distinguishes a wrong-drug error from a wrong-dose error?
A wrong-drug error involves dispensing an entirely different medication than prescribed, while a wrong-dose error involves the correct medication at an incorrect strength or amount per dose
A wrong-drug error means the wrong medication entirely was dispensed, while a wrong-dose error means the correct medication was dispensed but at the wrong strength/amount -- these are distinct, clinically meaningful categories. Wrong-dose errors apply to any dosage form, not just liquids, and wrong-drug errors frequently do involve LASA products.
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