Therapeutic Equivalence (Orange Book)
Therapeutic equivalence is the FDA determination that approved pharmaceutical equivalents meet its criteria, including bioequivalence, and are expected to have the same clinical effect and safety under labeled conditions. Orange Book A ratings include AB and several other codes.
Exam Tip
FDA A ratings establish therapeutic equivalence within the relevant group; B ratings do not. Match numbered codes such as AB1/AB2. Ratings inform substitution without overriding state law or the prescription. Bioequivalence does not allow tablets to contain 80-125% of labeled drug.
What Is Therapeutic Equivalence?
Therapeutic equivalence means that a generic drug can be expected to produce the same clinical effect and safety profile as its brand-name counterpart. The FDA publishes therapeutic equivalence evaluations in "Approved Drug Products with Therapeutic Equivalence Evaluations," commonly known as the Orange Book.
Requirements for Therapeutic Equivalence
A drug must meet ALL of the following:
| Requirement | Description |
|---|---|
| Pharmaceutical equivalence | Same active ingredient, dosage form, strength, and route of administration |
| Bioequivalence | Meets the applicable FDA evidence standard; this is not a rule that every patient concentration or tablet potency can range from 80% to 125% |
| Adequate labeling | Compliant with FDA labeling requirements |
| cGMP compliance | Manufactured under current Good Manufacturing Practice |
| Approved safety/effectiveness and quality | Approved products meet applicable identity, strength, purity, and quality standards |
Orange Book Rating Codes
| Code Prefix | Meaning |
|---|---|
| A | FDA considers the products therapeutically equivalent within the relevant group; substitution follows state law and prescription restrictions |
| B | FDA does not currently consider the products therapeutically equivalent |
Common A-Rated Codes
| Code | Meaning |
|---|---|
| AB | Bioequivalence demonstrated; most common for substitution |
| AA | Conventional dosage forms without known or suspected bioequivalence problems |
| AP | Injectable aqueous solutions |
| AT | Topical products |
| AN | Solutions and powders for aerosolization in general-use delivery systems |
Common B-Rated Codes
| Code | Meaning |
|---|---|
| BC | Extended-release products NOT shown to be bioequivalent |
| BD | Documented bioequivalence problems |
| BP | Potential bioequivalence problems |
| BX | Insufficient data for determination |
Generic Substitution Rules
| Factor | Details |
|---|---|
| AB-rated | May support substitution under state law; compare products within the same numbered AB group, when present |
| B-rated | Cannot be automatically substituted |
| State laws | Most states require or permit generic substitution for AB-rated products |
| Narrow therapeutic index (NTI) | Some states restrict substitution for NTI drugs (warfarin, levothyroxine, phenytoin) |
Pharmacy Technician's Role
- Check Orange Book ratings when selecting generic alternatives
- Verify the applicable FDA therapeutic equivalence rating and product group before any substitution allowed by state law
- Apply correct DAW code on insurance claims
- Refer B-rated products, different numbered AB groups, and state-law restrictions to the pharmacist; do not assume interchangeability
Exam Alert
Therapeutic equivalence is tested in both the Dispensing Process and Drugs/Drug Therapy domains. Key points: A ratings establish FDA therapeutic equivalence within the relevant group, while B ratings do not. State substitution law, prescriber restrictions, and specific product rules still apply.
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DAW Codes (Dispense As Written)
DAW codes are standardized numeric codes (0-9) used on pharmacy claims to indicate whether a brand-name or generic drug should be dispensed and who is requesting the specific product.
NDC Number (National Drug Code)
The NDC (National Drug Code) is a unique 10-digit, 3-segment numeric identifier assigned to each medication product in the United States, identifying the labeler, product, and package size.
Formulary
A formulary is a list of prescription drugs approved for coverage by a health insurance plan, pharmacy benefit manager (PBM), or healthcare institution, organized into tiers that determine patient cost-sharing.
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