Errors, Omissions, And Duplication

SECTION 1

Historical Context & Motivation

The recognition that medication-related problems could cause significant patient harm has evolved over decades of clinical practice and patient safety research. Early pharmacy practice focused primarily on compounding accuracy and dispensing correctness, but as healthcare delivery grew more complex—with patients seeing multiple prescribers and filling prescriptions at multiple pharmacies—the opportunities for errors, omissions, and therapeutic duplication multiplied dramatically. The pharmacist's role shifted from a product-centered dispenser to a person-centered clinician responsible for identifying and resolving these discrepancies before they reach the patient.

1999

To Err Is Human

The Institute of Medicine published its landmark report estimating that 44,000–98,000 Americans died annually from preventable medical errors, catalyzing a national patient safety movement and drawing attention to medication errors as a leading contributor.

2003

JCAHO National Patient Safety Goals

The Joint Commission introduced medication reconciliation as a formal patient safety goal, mandating that healthcare organizations compare a patient's medication orders against all medications the patient has been taking to identify and resolve discrepancies.

2006

ASHP Medication Reconciliation Guidelines

The American Society of Health-System Pharmacists formalized the pharmacist's role in medication reconciliation, establishing standards for identifying errors, omissions, and duplications during transitions of care.

2017

WHO Global Patient Safety Challenge

The World Health Organization launched "Medication Without Harm," aiming to reduce severe avoidable medication-related harm by 50% globally over five years, highlighting transitions of care, polypharmacy, and high-risk situations as priority areas.

2020–Present

EHR Integration & Clinical Decision Support

Electronic health records and clinical decision support systems became standard tools for detecting therapeutic duplications and drug interactions in real time, though pharmacist clinical judgment remains essential for interpreting alerts and resolving complex discrepancies.

Despite these advances, medication discrepancies remain alarmingly common. Studies consistently demonstrate that unintentional discrepancies occur in 30–70% of patients at hospital admission and discharge. The central question this lesson addresses is: How does a pharmacist systematically identify, classify, and resolve errors, omissions, and duplications within a person-centered treatment plan?

SECTION 2

Core Principles & Definitions

Understanding errors, omissions, and duplication requires precise terminology. In pharmacy practice, these three categories represent distinct types of medication discrepancies, each carrying unique risk profiles and demanding different resolution strategies. Recognizing them accurately is a foundational competency tested on the NAPLEX and practiced daily in clinical settings.

Medication Errors

Any preventable event that may cause or lead to inappropriate medication use or patient harm. Errors can occur during prescribing, transcribing, dispensing, administering, or monitoring. Examples include wrong drug, wrong dose, wrong route, wrong frequency, and wrong patient.

Omissions

The failure to prescribe, dispense, or administer a medication that a patient requires based on their clinical condition, comorbidities, or evidence-based guidelines. Omissions include untreated indications, missing prophylactic therapies, and medications inadvertently discontinued during transitions of care.

Therapeutic Duplication

The concurrent use of two or more drugs from the same pharmacological class or with overlapping mechanisms of action without clear clinical justification. This increases the risk of adverse effects and drug toxicity without proportional therapeutic benefit.

Medication Reconciliation

The systematic process of comparing a patient's current medication regimen against orders at every transition of care (admission, transfer, discharge) to detect and resolve discrepancies including errors, omissions, and duplications.

Person-Centered Assessment

An approach that considers the whole patient—including their health literacy, socioeconomic status, preferences, adherence barriers, and comorbid conditions—when evaluating a medication regimen for appropriateness, rather than evaluating each drug in isolation.

✦ KEY TAKEAWAY

Think of a patient's medication list like an orchestra score. A medication error is a musician playing the wrong notes. An omission is a missing instrument that the composition requires. A duplication is two musicians playing the same part simultaneously, creating dissonance rather than harmony. The pharmacist serves as the conductor, reviewing the entire score to ensure every part is correct, present, and non-redundant before the performance reaches the patient.

SECTION 3

Visual Explanation: The Medication Review Workflow

This workflow illustrates the four-step process of medication reconciliation. The pharmacist first obtains a comprehensive medication history (Step 1), compares it against current orders (Step 2), categorizes identified discrepancies as errors, omissions, or duplications (Step 3), and then resolves and documents changes to produce an optimized, person-centered medication plan (Step 4).

The diagram above represents a simplified but essential workflow that underpins every medication reconciliation encounter. Notice that Step 3—the identification phase—branches into three distinct discrepancy categories, each requiring a different clinical response. An error necessitates correction, an omission demands initiation of therapy, and a duplication calls for discontinuation of the redundant agent. All three pathways converge at Step 4, where the pharmacist exercises clinical judgment, communicates with prescribers, and documents the resolution in the patient's record. This systematic approach ensures that no discrepancy category is overlooked during the review process.

SECTION 4

How Errors, Omissions, and Duplications Occur

Root Causes of Medication Errors

Medication errors arise from a complex interplay of human, system, and environmental factors. Prescribing errors may result from incomplete patient assessment, failure to review allergies or renal function, look-alike/sound-alike drug name confusion (e.g., hydroxyzine vs. hydralazine), or dosing miscalculations. Transcription errors occur when verbal or written orders are incorrectly entered into the electronic health record. Dispensing errors involve selecting the wrong medication, strength, or formulation during the filling process. Administration errors occur at the point of care when the wrong drug, dose, or route is delivered to the patient. Each stage in the medication-use process presents unique vulnerabilities that the pharmacist must anticipate.

Mechanisms Behind Omissions

Omissions frequently occur during transitions of care—admission to the hospital, transfer between units, and discharge to home or a skilled nursing facility. A patient's home medications may not be continued upon admission because they were not captured in the medication history. Conversely, medications started in the hospital for acute conditions may be inadvertently omitted from the discharge prescription. Omissions also result from the failure to apply evidence-based guidelines: a patient with type 2 diabetes and established atherosclerotic cardiovascular disease (ASCVD) who is not prescribed an SGLT2 inhibitor or GLP-1 receptor agonist represents a guideline-based omission per 2023 ADA/ACC recommendations, recognizing that these agents provide cardiovascular and cardiorenal benefits independent of glucose lowering. It is important to distinguish this category of guideline-concordant omission from the more traditional medication reconciliation omission (a medication unintentionally dropped at a care transition), as each requires a different resolution approach and communication strategy.

Pathways to Therapeutic Duplication

Therapeutic duplication typically arises from fragmented care. When a patient sees multiple specialists who each independently prescribe within their area of focus, overlapping therapies can accumulate. A classic example is a patient receiving amlodipine from a cardiologist and nifedipine from a primary care provider—two dihydropyridine calcium channel blockers that provide redundant pharmacological activity while compounding the risk of hypotension, peripheral edema, and reflex tachycardia. Duplication also occurs when brand and generic versions of the same drug are prescribed simultaneously, or when a patient uses over-the-counter medications that duplicate prescription therapy (e.g., OTC omeprazole with prescribed pantoprazole).

💡 NAPLEX Tip

On the NAPLEX, you may be presented with a patient medication list and asked to identify the discrepancy. Train yourself to categorize each finding as an error (something incorrect), an omission (something missing), or a duplication (something redundant). This classification framework directly maps to the resolution strategy.

SECTION 5

Detailed Classification & Clinical Examples

This classification diagram organizes medication discrepancies into three columns—errors (red), omissions (amber), and duplications (violet)—each with four common subtypes and specific clinical examples. The resolution framework at the bottom shows that errors require correction, omissions require initiation, and duplications require discontinuation, all followed by thorough documentation and communication with the healthcare team.

Common clinical examples of errors, omissions, and duplications with their consequences and resolution strategies

Discrepancy Type	Clinical Example	Potential Consequence	Resolution Action
Wrong dose / drug-disease contraindication (Error)	Metformin prescribed at any dose for a patient with eGFR 28 mL/min (FDA labeling contraindicates metformin when eGFR < 30 mL/min/1.73 m²)	Lactic acidosis risk due to metformin accumulation in severe renal impairment	Discontinue metformin immediately per FDA labeling; select a renally appropriate alternative (e.g., linagliptin, which requires no dose adjustment)
Drug-disease contraindication (Error)	Metoclopramide prescribed for a patient with Parkinson's disease	Worsening extrapyramidal symptoms due to central dopamine antagonism	Discontinue metoclopramide and recommend an appropriate U.S.-available alternative antiemetic such as trimethobenzamide or ondansetron
Untreated indication (Omission)	Post-MI patient not prescribed a beta-blocker or high-intensity statin	Increased risk of recurrent cardiovascular events	Recommend initiation per AHA/ACC guidelines
Missing prophylaxis (Omission)	Patient on chronic corticosteroids without calcium, vitamin D, or bisphosphonate	Glucocorticoid-induced osteoporosis and fracture risk	Initiate osteoporosis prophylaxis per ACR guidelines
Same-class duplication	Patient taking both sertraline (SSRI) and escitalopram (SSRI)	Increased serotonin syndrome risk, excessive serotonergic activity	Discontinue one SSRI; taper as appropriate

SECTION 6

Worked Example: Comprehensive Medication Review

Consider the following clinical scenario. Mrs. Johnson is a 72-year-old woman admitted to the hospital for heart failure exacerbation. Her home medication list includes: lisinopril 20 mg daily, amlodipine 10 mg daily, metoprolol succinate 100 mg daily, atorvastatin 40 mg daily, aspirin 81 mg daily, and omeprazole 20 mg daily. Upon admission, the following medications are ordered: lisinopril 20 mg daily, amlodipine 10 mg daily, nifedipine ER 30 mg daily, carvedilol 12.5 mg BID, atorvastatin 40 mg daily, aspirin 325 mg daily, and furosemide 40 mg IV BID. The admitting physician also notes that Mrs. Johnson has type 2 diabetes (A1c 8.2%), atrial fibrillation, and a history of peptic ulcer disease. She is not on any anticoagulant. Let us walk through the systematic review.

Systematic Medication Review for Mrs. Johnson

Step 1 — Obtain and Verify the Medication HistoryFirst, verify the home medication list by consulting the patient, family members, the community pharmacy, and prior medical records. Confirm each medication's dose, route, frequency, and adherence. Mrs. Johnson confirms she takes all six home medications as listed and has been adherent.

Step 2 — Compare Home Medications Against Admission OrdersSystematically compare each home medication against the admission orders. Note that metoprolol succinate 100 mg daily from home has been replaced with carvedilol 12.5 mg BID (this may be intentional for HF—carvedilol has stronger evidence in heart failure). However, omeprazole 20 mg daily is absent from the admission orders. Additionally, nifedipine ER 30 mg daily has been added, and aspirin has been changed from 81 mg to 325 mg.

Step 3 — Identify ErrorsThe aspirin dose change from 81 mg to 325 mg daily appears to be an error. In a patient with established cardiovascular disease, low-dose aspirin (75–100 mg) is recommended for secondary prevention. Higher doses increase bleeding risk without additional cardiovascular benefit. Additionally, the switch from metoprolol to carvedilol should be verified—was it intentional? If so, the dose equivalence should be confirmed. Note that beta-blocker dose conversion between metoprolol succinate and carvedilol is an approximation, as these agents have differing pharmacological profiles (carvedilol is a non-selective beta-blocker with additional alpha-1 blocking activity). Published conversion references suggest metoprolol succinate 100 mg/day corresponds to approximately carvedilol 12.5–25 mg BID; therefore, carvedilol 12.5 mg BID falls within the lower end of the estimated equivalent range. Regardless of the starting dose selected, upward titration based on clinical response and tolerability is required, as no conversion table can substitute for individualized dose adjustment.

Errors identified: aspirin dose escalation (325 mg → should be 81 mg); carvedilol dose equivalence is approximate and requires clinical titration

Step 4 — Identify OmissionsThree significant omissions are present. First, omeprazole was discontinued without documentation—given her history of peptic ulcer disease and aspirin use, gastroprotection is essential and should be reinstated. Second, the patient has type 2 diabetes with an A1c of 8.2% and heart failure, yet no diabetes medications appear on either list; guideline-directed therapy should be addressed, and an SGLT2 inhibitor such as empagliflozin or dapagliflozin is particularly appropriate given its proven benefits in both heart failure and T2DM per 2023 ADA/ACC guidelines. Third—and critically—Mrs. Johnson has documented atrial fibrillation and is not receiving any anticoagulation therapy. Per AHA/ACC/HRS guidelines, the CHA₂DS₂-VASc score should be calculated to determine stroke risk and the need for anticoagulation. At age 72 with heart failure, diabetes, and female sex, her CHA₂DS₂-VASc score is at least 4 (age ≥ 65 = 1 point, HF = 1 point, diabetes = 1 point, female sex = 1 point), well above the threshold at which anticoagulation is strongly recommended. The absence of anticoagulation in this patient represents a high-yield, clinically significant omission that must be urgently communicated to the prescriber.

Omissions identified: omeprazole omitted at transition; no diabetes pharmacotherapy; no anticoagulation for atrial fibrillation despite CHA₂DS₂-VASc score ≥ 4 (high stroke risk)

Step 5 — Identify DuplicationsThe admission orders include both amlodipine 10 mg daily (continued from home) and nifedipine ER 30 mg daily (newly added). Both are dihydropyridine calcium channel blockers with the same mechanism of action. Concurrent use increases the risk of hypotension, peripheral edema, and reflex tachycardia without meaningful additive antihypertensive benefit. One should be discontinued.

Duplication identified: amlodipine + nifedipine (two DHP calcium channel blockers). Recommend discontinuing nifedipine.

Step 6 — Resolve, Document, and CommunicateContact the admitting physician to recommend: (1) correct aspirin to 81 mg daily, (2) confirm carvedilol initiation is intentional and plan for dose titration based on clinical response and tolerability, (3) restart omeprazole 20 mg daily for gastroprotection, (4) discontinue nifedipine ER, (5) assess and initiate appropriate diabetes therapy—empagliflozin or dapagliflozin is strongly preferred given the concurrent heart failure (hold if hemodynamic instability is present during acute admission), (6) calculate the full CHA₂DS₂-VASc score, confirm the absence of absolute contraindications to anticoagulation, and initiate a guideline-recommended oral anticoagulant (e.g., apixaban or rivaroxaban) for stroke prevention in atrial fibrillation. Document all interventions, rationale, and physician responses in the medical record.

Total discrepancies resolved: 2 errors corrected, 3 omissions addressed (including high-priority anticoagulation for AF), 1 duplication eliminated

SECTION 7

Detection Strategies: Strengths & Limitations

Multiple strategies exist for detecting errors, omissions, and duplications, each with distinct advantages and shortcomings. Understanding these trade-offs is critical for pharmacists who must select and combine approaches to achieve optimal patient safety outcomes.

Comparison of detection strategies for medication discrepancies

Detection Strategy	Strengths	Limitations
Manual Medication Reconciliation	Highly adaptable; allows clinical judgment; can incorporate patient interview nuances; detects context-dependent omissions	Time-intensive; dependent on clinician knowledge; susceptible to human error and fatigue; inconsistent across providers
Clinical Decision Support (CDS) Alerts	Automated; consistent; real-time at point of prescribing; excellent for detecting duplications and drug-drug interactions	Alert fatigue leads to overriding; limited ability to detect omissions; high false-positive rate; requires ongoing maintenance
Pharmacist-Led MTM (Medication Therapy Management)	Comprehensive review; patient engagement; identifies adherence barriers; addresses all three discrepancy types simultaneously	Resource-intensive; requires protected pharmacist time; limited scalability; reimbursement challenges in some settings
Standardized Checklists / Protocols	Reduces variability; easy to train staff; ensures systematic review of high-risk categories; supports regulatory compliance	Rigid; may not capture novel or atypical discrepancies; risk of "checkbox" mentality without genuine clinical thought
Interprofessional Team Rounds	Multiple perspectives; real-time resolution; fosters collaboration; highly effective in inpatient settings	Scheduling challenges; not available in all settings; dominant voices may suppress contributions; variable pharmacist inclusion

✦ KEY TAKEAWAY

No single detection strategy is sufficient in isolation. Just as an aircraft's safety depends on multiple redundant systems—pilots, co-pilots, checklists, automated instruments, and air traffic control—medication safety depends on layering manual pharmacist review with automated clinical decision support, standardized protocols, and interprofessional collaboration. The pharmacist's unique value lies in synthesizing information from all these sources and applying clinical judgment to complex, patient-specific scenarios that technology alone cannot resolve.

SECTION 8

Connection to Advanced Practice & Regulatory Standards

The identification and resolution of errors, omissions, and duplications is not merely a clinical skill—it intersects with regulatory requirements, quality metrics, and advanced pharmacist practice models. Understanding this broader context prepares pharmacy students for practice environments where medication safety is increasingly tied to organizational performance and reimbursement.

Progression from foundational concepts to advanced practice applications

Foundational Concept	Advanced Application
Identifying individual medication errors	Root cause analysis (RCA) and failure mode and effects analysis (FMEA) to identify systemic vulnerabilities that produce recurring error patterns
Manual medication reconciliation	Comprehensive medication management (CMM) as part of value-based care models, with pharmacist-driven collaborative practice agreements
Detecting therapeutic duplication at dispensing	Pharmacogenomic-guided deprescribing, where genetic data informs whether a patient metabolizes drugs from the same class differently, justifying or contraindicating concurrent use
Addressing omissions based on clinical guidelines	Population health analytics using EHR data to identify cohorts of patients with systematic omissions (e.g., diabetic patients without statin therapy across an entire health system)
Documenting interventions in patient records	Quality improvement metrics (CMS Star Ratings, HEDIS measures) that track medication safety outcomes and link pharmacist interventions to organizational performance and reimbursement

Looking forward, the pharmacist's role in detecting and resolving medication discrepancies will continue to expand. Artificial intelligence and machine learning algorithms are being developed to predict which patients are at highest risk for medication discrepancies, allowing pharmacists to prioritize their review efforts. Collaborative practice agreements in an increasing number of states allow pharmacists to independently modify medication regimens to correct errors, fill omissions, and eliminate duplications without requiring a new prescription for each change. These advanced practice models position the pharmacist as a central figure in optimizing medication use across the healthcare continuum.

SECTION 9

Practice Problems

PROBLEM 1 — CONCEPTUAL

A pharmacy student is reviewing a patient's medication list and discovers that the patient is prescribed lisinopril 10 mg daily for hypertension but has a documented history of angioedema with enalapril. The student is unsure whether to classify this finding as an error, an omission, or a duplication. Which category does this discrepancy represent, and why?

PROBLEM 2 — BASIC CALCULATION

During a medication reconciliation at hospital discharge, you compare the admission medication list (12 medications) against the discharge orders (14 medications). You identify 2 medications present at admission but absent at discharge, 4 new medications added during hospitalization, and 1 instance where the same drug appears under both brand and generic names on the discharge list. Classify each finding and calculate the total number of discrepancies requiring resolution.

PROBLEM 3 — INTERMEDIATE

Mr. Patel is a 65-year-old man with type 2 diabetes (A1c 7.8%), hypertension, CKD stage 3b (eGFR 38 mL/min/1.73 m²), and a history of NSTEMI six months ago. His current medications are: metformin 1,000 mg BID, glipizide 10 mg BID, lisinopril 40 mg daily, amlodipine 10 mg daily, hydrochlorothiazide 25 mg daily, and aspirin 81 mg daily. Identify all errors, omissions, and duplications in this regimen.

PROBLEM 4 — APPLIED

You are a pharmacist at a community pharmacy. Mrs. Garcia presents with prescriptions from three different providers: (1) Dr. Smith (PCP): lisinopril 20 mg daily, atorvastatin 40 mg daily, metformin 500 mg BID; (2) Dr. Lee (cardiologist): losartan 50 mg daily, rosuvastatin 20 mg daily, carvedilol 6.25 mg BID; (3) Dr. Chen (endocrinologist): metformin 1,000 mg BID, empagliflozin 10 mg daily. Mrs. Garcia states she has been taking all the medications from all three doctors. Identify and classify every discrepancy, and outline your communication plan to resolve them.

PROBLEM 5 — CRITICAL THINKING

A hospital system reports that its medication reconciliation program identifies discrepancies in 45% of admitted patients, but only 60% of identified discrepancies are resolved before discharge. The pharmacy director asks you to design a quality improvement initiative to increase the resolution rate to 90%. Consider the root causes of unresolved discrepancies and propose a multi-faceted strategy that addresses system, process, and human factors.

SUMMARY

Summary

Medication discrepancies fall into three fundamental categories: errors (incorrect drug, dose, route, frequency, or contraindicated therapy), omissions (missing indicated therapies, discontinued medications at care transitions, or absent prophylaxis), and therapeutic duplications (same-class agents, brand-generic overlaps, or OTC-Rx redundancies). The pharmacist identifies these discrepancies through medication reconciliation—a systematic process of obtaining a complete medication history, comparing it against current orders at every transition of care, and classifying each finding to determine the appropriate resolution: correct errors, initiate omitted therapies, and discontinue redundant agents.

Effective discrepancy detection requires combining clinical decision support alerts with pharmacist clinical judgment, interprofessional collaboration, and person-centered assessment that considers the whole patient—comorbidities, renal function, allergies, adherence barriers, and treatment goals. Every intervention must be thoroughly documented, communicated to the prescriber, and followed up to ensure resolution. This competency is fundamental to NAPLEX readiness and to the pharmacist's evolving role as a medication therapy expert who safeguards patient outcomes across the healthcare continuum.